Tuesday, July 31, 2007


(NOTE: This was written in 2003. Use it only for background information. In later posts I'll show the methods & procedures I'm presently using, tell you why some things worked better than others.)

Head Work

Die Grinder is big. Two-handed sort of tool. Home machinists usually have one from Sears, Sioux or Black & Decker. The barrel of the high rpm motor is of a standard diameter so you can use a die grinder holder on your lathe; Po' Boy Tool Post Grinder.

Real die grinders are used by Tool & Die markers to literally sculpt steel. Big die grinders, usually pneumatically powered, sometimes so large they're suspended on a counter-poise. Use one of these, solid carbide burr, you gotta dress for the occasion.

Building a big-bore VW for use in an airplane, there isn't a lot of head work; nothing like what you put into a racing engine. At propeller speeds the flow-rate of even the largest big-bore stroker is small in comparison to something designed to turn seven grand at cruise and peak-out around nine. Still, there is some work to do. Opening up the chambers to accept larger jugs leaves a wide ledge at each end of the valve recess. A flow bench will show that the heads breathe better if the ledge is set back so as to unshroud the valve. Bill Fisher covered this in his 1970-era `How to Hotrod Volkswagen Engines,' which remains in print and is still valid for such things as head work. When you get a copy of Bill's book be sure to study the flow-rate charts. Then sit down and calculate the flow rate for your engine, assuming 100% volumetric efficiency at your designed cruising rpm.

Be prepared to be underwhelmed :-)

Now go back and look at the charts. Notice that your rpm indicates stock single-port heads will do pretty well without any unshrouding or smoothing. Up to you; you're the Mechanic-in-Charge.

I always clean up the heads. Force of habit as much as better performance. The big advantage to this type of work is that the improvement ends up being built right into the engine. Like bigger displacement, better breathing isn't something you have to add on or periodically replace.

Besides unshrouding the valves there's a few sharp edges in the chambers that need to be smoothed. Ever seen air-flow through polarized filters? Comparing the air negotiating a sharp corner to one that has been properly radiused is a real eye-opener when you can see the improvement in the flow. Here again, let Bill's book be your guide. Lotsa good pictures.

Most of the head-work requiring a die grinder is simple smoothing. The head is a casting; the ports have rough surfaces, reflecting the surface of the cores, a lot rougher than the fins and other surfaces which reflect the permanent metal molds used to cast VW heads. (I'll mention those other surfaces in a minute.)

We usta think we got more flow if the passages had a mirror finish. Turns out, according to Pratt-Whitney and NASA, there's no improvement after the surface texture hits about #600. (I didn't believe them, of course. But the flow bench did :-) Why this is true has to do with the fact that fuel/air mixture is not a perfect gas. Flow bench runs straight air unless you dope it with a suspended colloid such as smoke.

Point here is that all you need to do to see a good increase in your in-flow (and thus in your VE) is to get the ports dead smooth. Don't worry about a polished finish.

The way to do that is to start with a flapper wheel or sanding drum in your die grinder and knock down all the casting imperfections. Your hand is your best gauge here. As-cast, the ports feel like rough concrete. Your job is to make them feel like smoothly sanded wood.

Once you've gotten rid of all the peaks and ground out any inclusions and smoothed the trench, you simply shift to a finer abrasive and remove the marks of your first effort. Then do it again. And again.

By the time you've gone down about three graduations in your abrasives (which are also covered in Bill's book, I think... ) the surfaces will be uniformly smooth and have an even, frosted appearance that offers just the slightest hint of tooth to the touch. Go ever everything about three times at that level then shift to your finishing grade, whatever it happens to be. But be warned: Each time you graduate to a smaller size it will take about twice as long to remove the marks from the previous grit. If you've got a die grinder and a box of Cratex hobbs expect to spend about four hours per head.

I didn't have all that stuff when I was a kid. I did my first heads using a quarter-inch drill motor. Worked okay but I think I spent about thirty hours doing a pair of heads; no big deal when you're a kid, right? :-) Nowadays, if I didn't have a die grinder I'd probably shoot myself rather than stand at the bench for thirty hours.

Which brings us to the point of all this.

Some time ago a fellow wrote to ask if he could do a set of heads using a Dremel tool. I told him I didn't know. Recently, two other fellows asked the same question and I felt that justified looking into it.

The answer is a qualified `yes.' It takes quite a bit of time but I found I could unshroud the valves and clean up the sharp edges under the exhaust valve using a hobby-type tool, an inexpensive thing I picked up at Harbor Freight. And you can smooth at least part of the ports. But the tool was too fat to get right into the ports, and it didn't come with hobbs that were long enough to reach. So yes, you can do most of the job, and you should see some improvement in your flow, but not as much as when they were properly smoothed for their full length.

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As for the fins, I'm sure I've covered this before but I want to keep all of this together, so here it comes again.

You have to remove all of the flash between the fins. I use a pneumatic riffler for this but a sabre saw or even a hand saw will work for most of the fins. Up around the exhaust valves you must ensure several very critical passageways are not blocked. I've posted a drawing of the heads and the passageways are clearly shown but you can see them for yourself the first time you examine a head. Keep in mind that the exhaust stack and the exhaust valve guide are principle sources of heat in this area. The head is designed to have the air flow down thru the head; this is reflected by the drafting ratio in the mold. Air expands as it absorbs heat so the exhaust-side of any cooling air channel tends to have greater volume than the intake-side. Don't upset that ratio or you'll see a pressure drop, meaning the air is not picking up as much heat as before. The pressure differential in all cases should be between six and nine inches of water and this is something you should focus your attention on during your test flights. An airspeed indicator rigged with the pressure port to the upper plenum and the static port to the exhaust area, usually the space forward of the firewall, should show a pressure differential of about 90 miles per hour from inlet to outlet. Or you can rig a barometer or even an altimeter to indicate the pressure differential.

Cooling air pressure differential is not something you want to leave to chance. The Volkswagen engine was designed to use a blower having an output proprotional to the speed of the engine. To properly cool the engine using ram-air you must pay the keenest attention to a host of 'unimportant' details. Not only must the upper plenum provide sufficient pressure, your lower shrouding should provide sufficient containment to force maximum rate of flow through the hottest parts of the head. You can instrument these areas with inexpensive thermistors wired to a single gauge and read via a rotary switch or whatever; something sturdy but temporary.

Adjustments to the system take the form of changing the inlet & exhaust area. I consider the late John Thorpe to be the best authority I've read on cooling horizontally opposed aircraft engines. He wrote a series of articles for `Sport Aviation' or its precursor. See if you can track down his articles. If you can't, perhaps someone can paraphrase them or extract just the equations and post them to the archive.

Once you've cleaned up your fins, seal up the chambers, ports and valve gallery then blast the shit out of the fins with coarse abrasive media at low pressure. What you want to achieve is a rough surface. In fact, blasting the cast fins with coarse media will result in a significant increase in the surface area of the fins.

But don't blast anywhere that will eventually be inside the engine. Abrasive media has a habit of embedding itself in non-ferrous metals, coming loose as the metal goes through heat cycles. Bottom line is that if you don't want abrasive in your bearings, don't allow it to get on the engine to begin with. (Real shops use non-abrasive media for cleaning heads and the like. Walnut shells [which is what I use] or plastic beads. Frangible media such as glass beads comes under the same ban as abrasives.)

(So why is it okay to use abrasive rules for porting & polishing but using abrasive media is evil? Mostly because the ports and chambers are pretty small compared to the valve gallery, but more so because of the nature of the media. Blasted media tends to embed itself whereas the media on a sanding wheel does not. [A 30x glass and a good light will let you answer this question for yourself.])

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Finally, one of the most difficult lessons to learn with Thermal Barrier Coatings is that the surface must have a roughness equal to #80. The best way I found to achieve this on aluminum is with plain old fashioned silica sand. And yes, it breaks the rules big-time.

(NOTE: Starting in 2005 I began using aluminum oxide abrasive rather than sand. It is more dangerous to the engine but less so to the person doing the blasting.)

To coat the tops of the pistons I was able to mask them off pretty well. After blasting I ran them through the ultrasonic cleaner then a zero-tolerance degreaser and finally into the spray booth for spraying with the TBC. They get cured in a 350 degree (F) oven and are allowed to cool in the oven for 24 hours or until hell freezes over, which is how long it seems when you're dancing around waiting to see if you've just fucked up $200 worth of pistons. Which I did, more than once, except they were gimmes; only pistons from out of the junk box. And you can remove a bad coating by blasting... but don't expect it to come out evenly. Blasting off the bad coating then taking a clean-up cut of about .0015 works. Indeed, you end up with a mirror bright beauty... which you must then carry over to the blasting cabinet and hose to a dull, frosted surface. Life is strange in the engine room :-)

The beautifully smoothed heads got the same treatment. I use solid copper head gaskets on heads that have been bored for larger jugs and you don't want the TBC to be UNDER the gasket, which means masking it off. If you can. I tried several methods. I wasn't entirely satisfied with any of them. Masking tape didn't work; after being stripped away (TBC dried but not baked) there was enough residue from the adhesive to contaminate the TBC. I ended up making aluminum rings about five thou wider than the copper gaskets and swaging them into place as a mask. The second time I did it I remembered to provide some means of pry them out of the chambers without scratching the sprayed TBC :-)

The piston tops, combustion chambers and exhaust stacks received the basic Thermal Barrier Coating. Because of its hyper-eutectic nature, baking at 350F cascades a melting process that results in ceramic- metallic alloy bonded to the aluminum substrate. Because of its ceramic nature, the surface pretty much ignores heat.

How does it work on a full-size engine? I don't know. But soon will.

The reason I mentioned it here is because of the violation of the `no abrasives' rule. Silica is definitely an abrasive. But if there was any abrasive residues left on the surface, they are now encapsulated in a cer-met alloy that you literally can not chip with a ball peen hammer. (I've spent three years convincing myself this stuff is worth the effort. I really wanted that shit to fail... save me all the trouble early on. I still don't know. But I'm starting to lean toward `Hopeful' on the self-delusion meter :-)

What's all this for? The main goal is to extend the life of the valves through better management of their heat load. I might see some improvement in power output because of a slightly higher BMEP. Or I might not. The folks who make the coatings don't have a lot of data on air-cooled engines and liquid cooled's don't even come close to the problems we have.


Sunday, July 29, 2007

Crankcase Fasteners

A couple of times of year, usually in the summer, I receive a message from an angry young man trying to dismantle a Volkswagen engine. In many cases he has resorted to chisels or screwdrivers; in one case a wedge for splitting firewood was used.

The engine is junk, of course. Which is okay because it is a stupid engine anyway (he sez).

Amazingly, in a few cases it is a Group Letter. The Mechanic-in-Charge has sought advice from a gaggle of friends, all of whom agree there is something wrong with this crankcase.

What's wrong is that the fellow has failed to remove all of the fasteners. Or they have left the oil pump in place. Or perhaps the sump plate. But nine times out of ten, suggesting that might be the cause earns me a nasty-gram, often larded with profanity.

I add the fellow to the Kill File and get on with my life.

I'm sure no one reading this has ever forgotten to remove the oil pump before trying to split the case. And I'm sure no one has ever overlooked the stud tucked under the #1 cam bearing. But you may want to print this out, just in case you ever run into someone with a seriously stuck crankcase.

Be sure to mention that they must remove both the oil-pump cover and the oil-pump itself. If they don't have a pump puller then they may elect to remove the oil-pump studs, or at least two of them, so long as they come from the same side of the crankcase. The same applies to the sump plate in that both the sump plate and the oil strainer must be removed.

You will note there is one stud anchored in the right-hand case-half. (With Volkswagens orientation is always relative to the vehicle. That is, the front of a VW engine is where the flywheel is attached; the fan pulley is on the rear of the engine. In the same vein, the #1 Main Bearing is the one nearest the flywheel. Ditto for the cam bearings. These are the conventions established by the designer of the engine seventy-five years ago and apply to the thirty-million or so Volkswagen engines manufactured since. ) So make sure they haven't overlooked the odd right-hand stud tucked away behind the distributor.

Then there are the three bolts. Sometimes the engine is so clotted with dirt and oil that the lower bolt nearest the flywheel gets overlooked. Have them dig around until they've found and removed all three.

The six M12 studs are difficult to miss but sometimes they fail to remove the washers. In rare cases a washer can jam the threads and hold the case halves as if they were still bolted together. So have them lay-out the six large nuts with their large, thick washers.

Then there are the twelve nuts & washers for the remaining studs, including the odd-ball righty. The one most often over-looked is the one below the #1 cam bearing, which is often completely concealed beneath twenty years of poor maintenance. Make sure they chip away the grunge and remove the hidden nut and its washer.

If the fasteners are neatly arranged on a piece of newspaper it makes it easier to tell if you've found them all. Another good check-off is to physically touch the location of each stud as you count them off.

Once all of the fasteners have been removed along with the pump and sump-plate I prefer to split the case using only the strength of my hands. This isn't as difficult as it sounds, assuming the case isn't fitted with shuffle-pins. Simply grasp the opposite ends of the case at the opposing 'corners.' That is, one hand is positioned near the upper tranny flange, the other under the oil pump. Volkswagen has provided pads in those areas to allow the case to be 'started' with a rubber mallet but if you fiddle with it you'll see you can bring your thumbs to bear against the pads while your hand bears on the other half of the case. By applying pressure alternately you can 'walk' the case apart.


(Note: I've uploaded the drawing above to the engine archive on the Chuggers Group. The drawing is in it's native format [ie, DeltaCAD] meaning it may be manipulated as required. The drawing isn't especially accurate but it's more than a guess :-)

Friday, July 27, 2007

Basic Jugs - IV 1/2

Several people wondered why I failed to mention checking the fit of the piston rings in their grooves. So I went back and mentioned it. Now allow me to offer you a whiff of Mechanical History.

Back in the Good Ol' Days, which really weren't, the Ring & Valve Job was the staple source of income for the majority of mechanics. Thanks to inadequate air cleaners and no oil filtration at all, somewhere between 20,000 and 40,000 miles of service the engine of every automobile became so worn that the compression would fall so low that the engine could not be started. And if you could get it running, it was liable to burn as much oil as gas. That's when you'd deliver Ol' Betsy up to the local mechanic who perform the Ring & Valve Ritual.

Most people don't know it but the primary sealing surface needed to ensure good compression is not the fit of the piston ring to the wall of the cylinder but the fit between the ring and the top and bottom of its groove. Pulling the pistons and honing the walls of the cylinders was part of the classic Ring & Valve job but the critical work took place in the back of the shop, where the pistons were chucked into a lathe and their grooves re-machined so as to return their upper and lower surfaces to truth, meaning perfectly perpendicular to the axis of the piston. Doing so also widened the groove, requiring the fitting of wider rings, a stock of which was usually kept on-hand. A good machinist could 'overhaul' a piston so that the grooves were a nice match for the next available over-size ring but when they missed they simply honed-down the ring to match the groove, plus the usual tolerance of one to three thousandths. There were machines that could hone four rings at a time but small rural shops usually relied upon boy-power, a surface plate, and a sheet of fine sand-paper flooded with kerosene. The boy's reward was being allowed to test-drive the 'tight' engine around the block a time or two. (Yes, that's me behind the wheel of the Model A, out behind Leduc Motors, the Ford dealer in Turlock, California.)

Things are a bit different today :-) Nowadays, when you buy a set of replacement Pistons & Cylinders for your Volkswagen engine the fact the pistons are already installed in the barrels is good evidence that the rings fit their grooves. They might be a tad too loose but you know they can't be too tight, otherwise they wouldn't be able to compress the rings enough for the piston to fit in the barrel. This reflects the fact that mass-produced replacement parts are manufactured to a looser standard - - a wider range of tolerance - - than the factory-produced original.

If you were building an engine meant to run hours at a time above 5,000 rpm you're probably using forged pistons fitted with high rpm rings. That's when you concern yourself with the precise fit of the rings in their grooves. (Indeed, you might even buy blank forgings and machine the grooves yourself.) But for low rpm applications, such as spinning a propeller, you generally don't. Other than to ensure the ring moves freely in its groove there is little to be gained in measuring the precise amount of clearance because in the practical sense there isn't anything you can do about it other than to order a new set of P&C's... with the strong probability they will be no better.

When assembling an engine from a collection of after-market parts there are many areas in which the close attention of the assembler can pay a significant dividend in terms of power, durability or efficiency. But this isn't one of them.


Wednesday, July 25, 2007

Basic Jugs - IV

Due to their higher operating temperatures, in air cooled engines the piston ring gap is wider than on liquid-cooled engines. For after-market Volkswagen cylinders you want a minimum ring gap equal to 0.0045" per inch of bore. The jugs shown in these articles have a bore of 94mm - - about 3.7" in diameter. 3.7 x .0045 = .01665. Maximum would be about .005" per inch of bore or about .0185" but you could go as large as .006" per inch - - about .022" - - before you began to see a decline in performance.

What cannot be allowed is a gap that is too small. That is, our negative tolerance is zero, meaning the gap can’t be any smaller than our nominal .017" although our positive tolerance could be as much as .005". Written out it would look like this:

RING GAP = 0.017, -0 / +.005

Select a cylinder. Wipe the bore dry using a paper tower (*). Find the baggie matching that cylinder’s number. Lay-out the piston rings and wipe them dry. Starting with the Upper Compression ring, gently stone the edges of its gap. Use your 3x loupe to inspect your work. It should take only two or three light passes of the stone to break the sharp edges of the gap. Repeat this procedure for all four rings for that particular cylinder. After stoning, wipe the edges with a clean paper towel.

Select the Upper Compression ring. Insert it into the top of the cylinder’s bore. Using a clean piston, press the ring into the bore for a distance of about 1". Use feeler gauges to determine the gap.

Remove the ring, turn the cylinder up-side down and repeat the procedure on the bottom of the cylinder’s bore. The gap should be identical, indicating the bore is not tapered; that it is a true cylinder.

Repeat this procedure for the Second Compression ring. Since we now know the bore is true there’s no need to check the ring at the lower end of the barrel.

The Oil Scraper Rings have an entirely different mission than the compression rings. These rings are meant to provide a compliant contact with the cylinder wall and are a loose fit in the barrel. They will be pressed into contact with the cylinder wall by being installed atop the corrugated band. They require the same minimum gap as the other rings but their upper limit may be as wide as .030" and they would still function effectively. Check these rings in the bottom of the bore, pressed in about one-half of an inch.

Repeat this procedure for all four cylinders.

If the ring gap for either of the compression rings is too large you must order & fit a new set of rings.

If the ring gap for any of the rings is too small you must file the gap wider, being sure to stone the edges after filing.

If you need to widen a ring-gap the most common means is through the use of a special tool designed for that purpose called, appropriately enough, a piston ring filer.

As the pictures show, piston ring filers are widely available. Given the wild diversity of designs I'll leave you to decide which is most suitable for your needs.

As a point of interest I have a ring filer out in the shop, somewhere. I can’t remember when I bought it but I recall it cost nearly three dollars. I still use it for little piston rings but for everything else, I use a plain old-fashioned file. (Hint: Clamp the file in a vise and draw the ring toward you. It would be wise to practice on a couple of junk rings first.)

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In checking the rings, all passed a .018" feeler gauge save one, which was a tad tight. I touched it up with the file and re-dressed the edges. As engines go, this one is proving to be a bit less trouble than most (furiously knocking on wood :-)

I'll be applying a cermet Thermal Barrier Coating to the jugs so the next step is blasting them with abrasive media. To prevent damage to the ring lands and make clean-up a little easier, the body of the piston gets masked-off, leaving only the crown exposed.

After you’ve dressed & checked the rings, if you are not going to apply a thermal barrier coating you may go ahead and re-install the rings to the pistons. Remember that on the oil control ring the corrugated band is installed first, then the two scrapers, one on the upper edge of the band, the other on the lower. As for the compression rings, be sure to check their orientation.


Tuesday, July 24, 2007

Basic Jugs - III

In manufacturing a cylinder barrel the cast iron blanks are first bored with a multi-point tool then brought to their finished size with an abrasive hone. The last step is to scour the honed bore with a coarser, reciprocating hone operated at a fairly low speed. This produces the characteristic cross-hatching, the grooves of which hold a significant quantity of oil that facilitates the process of breaking-in the freshly assembled engine.

The grooves also hold a residue of carborundum, stripped from the coarse hone. These particles can produce vertical scoring on start-up, creating wounds in the cylinder wall that grow progressively worse over time. Although there are a number of high-tek ways to remove the residue (ultra-sound is one) but the cost of doing so can push the price of a set P&C's right out of the market-place.

Fortunately, there is an effective low-tek method developed in the early days of automotive maintenance. You simply scrub the bores of your newly honed cylinder with an abrasive cleanser. For the last seventy years or so Bon-Ami cleanser has been the preferred stuff but other cleansers containing pumice, chalk or diatomatious earth work equally well. These relatively mild abrasives break-down under pressure and are no threat to the innards of your engine. Alas, you can’t use any of the modern-day scouring powders which often contain such lovely stuff as powdered glass and chlorine bleach. Chlorine is about the last thing you want anywhere near cast iron and powdered glass, while it does a beautiful job of removing the porcelain from the kitchen sink, is almost as bad for your engine as carborundum.

There are two schools of thought on how to scrub your jugs. One sez the only proper way to do it is up & down, the way God intended. But there’s a few heathens who insist on doing it roundy-round, especially those who advocate the use of Lava soap rather than Bon-Ami. Others use Boraxo Powdered Hand Soap; a few mix their own formulations.

Personally, I’ve not noticed any difference at the finish line. In fact, the main difference is between those who do scrub their jugs versus those who don’t. The former make up a lot of the familiar faces in finish-line photos while the latter are rarely seen at all. Some (including me) will argue it isn’t the scrubbing but the overall attention to detail that is the key to a properly assembled engine. Scrubbing your jugs is just another of the many ‘unimportant’ details the newbies joke about and never do since it serves no purpose. According to them.

As to how to give your barrels a bath, the holes for the head-stays divides the barrel into quadrants. Put the barrel into your wash bucket, tub or whatever, submerged in water. Dampen your sponge, charge it with a couple of squeezes of Bon-Ami, 20-Mule Team or whatever, pick up the jug in one hand, the sponge in the other and give one quadrant twenty strokes. Dip, re-charge the sponge, rotate to the next quadrant and repeat. After doing all four, rinse the barrel and the sponge... and do it all over again. Four more times. Fig 1 shows the area set up for scrubbing jugs.

If you’re a Lava Man, same routine except you’re going roundy-round whilst everyone else is doing it up & down.

Expect it to take fifteen to twenty minutes per jug.

But before getting all wet & sweaty go find a big pot, fill it with water and set it to boil. If you’ve got a stove in your shop (I do!) things are a bit easier than if you have to work in the kitchen. Or the back yard. Working outside, the best boiler is probably a barbeque. And yes, you want the water boiling, or as close to it as you can get at your elevation.

You’ll also need a piece of stiff wire to fish the jugs out of the boiling water and a pad of newspaper or cardboard to sit them on after they are sprayed. As in WD-40. Because if you aren’t standing there Johnny-on-the-Spot with your can of WD-40 at the ready, your jugs are rust right before your eyes. And yes, WD-40 is okay for this job. In fact, that’s what the ‘WD’ stands for: Water Dispersant, formulation #40. Developed for Convair back in their Atlas missile days.

Ready to scrub? Then go to it.

After scrubbing a jug, take it over to the hot pot, hook the wire through a hole and slosh it in the boiling water. Do a good job of it; you want that jug to get hot. While it’s getting hot you’re grabbing a rag to use to hold on to the can of WD-40 (soapy hands, etc.).

Raise the hot, rinsed jug out of the water, orient it so the over-spray won’t kill anything and soak it down with WD-40. Let it drip a bit then sit on the drain pad, recover your wire and get busy with the next one.

Figure on spending an hour or more per set of jugs. And that doesn’t count the preparation & clean-up. (Hint: Doing more than one set of jugs at a time will reduce your overhead.) (Double Hint: Add another notch to the fin showing which set the jug belongs to.)

Despite conventional wisdom WD-40 is not a protective coating. It was - - and is - - a water dispersant and while handy for other things, protecting bare metal isn’t one of them. So make up a pad of paper toweling, soak it with motor oil and wipe down the bores of your scrubbed jugs. Careful! The last one out of the pot will be too hot too touch. Try doing a bit of clean-up first; give it a chance to cool down. Okay; now wipe them down and put them back into the box according to their notches/numbers. (Fig 3 up at the start of the article shows the scrubbed jugs cooling in the shade.)


PS -- Some one familiar with my shop wondered why most of the photos were taken in the patio.

I've got a nice shop with a lot of tools. A nice private shop. In this engine assembly series I'm sticking to basic methods that don't need a lot of tools. I no longer offer engines for sale. I don't encourage visitors, and there are things in my shop I prefer to share only with family & friends.

This will not effect the quality of the engine in any way. Indeed, the pictures are probably a more realistic representation of what the average builder is doing. -- rsh

Monday, July 23, 2007

Basic Jugs - II

Basic Jugs - II

If you’ve never installed nor removed piston rings, buy yourself a piston ring tool like the one in the photo. Harbor Freight sells them. (The tool in the picture is about forty years old. It still looks new because I generally use my hands.)

Small pistons, you can use your bare hands to install/remove the rings... if you know how and are only doing one engine at a time. If you do a lot of engines you generally use a tool. Some piston rings have over-lapping ends, others are tapered and you may be forced to use a tool since your thumbnails can’t get a grip on the oddly shaped gap. When the oil scrapers are steel, as they are on this particular set of jugs, you use your hands regardless. Steel oil-scraper rings are very flexible and must come off before the corrugated band can be removed (and are installed after it is in place). (The compression rings are cast iron and are quite brittle. Using the tool can save you some grief.)

Provide yourself with pencil, paper and four baggies; sandwich bags will work fine. Then round up the most accurate scale you can find. You’ll also need a coffee can filled with enough mineral spirits to submerge a piston, some means of removing metal from the piston and about half a sheet of #600 wet & dry sandpaper. If you have a handy method of holding the piston you can use a rotary file for the coarse removal but you’ll need flapper wheels or some other abrasive removal method for the fine work. You’re also going to need a small, fine-grained whetstone; the sort of thing you’d use to sharpen a pen knife. A 3x loupe or reading glass will come in handy. Finally, you need a set feeler gauges. But just round up the last three; we probably won’t get to use them during this session.

Plus paper towels, wash-bottle of lacquer thinner, good lighting, cuppa hot coffee... the Usual Stuff.

(Note: They rings must fit their groove, in that you don't want a 1mm ring in a 2mm grove. They should rotate easily. If they don't, try soaking them in solvent. Often times cosmoline or other preservative will harden between the ring the land, locking the ring in place. Ring/groove clearance varies from slightly over a thou to as much as four thou, depending on the application. For a low rpm engine such as the one described here, so long as the ring rotates freely in its groove, it should work okay.

While that may sound a bit casual to some, optimum ring clearance is usually obtained by lapping over-size rings for a precise clearance to forged racing pistons. While the time and expense may be justified for a racing engine such close tolerance in this particular area can be a detriment to the durability of a low-rpm engine.)

Make yourself four small paper tags about the size of a double-wide postage stamp. Number the tags 1 through 4. Put one in each of your bags. Start with your #1 piston and remove the top ring. That is, find the ring-gap, push the other side of the ring fully into its groove so that the gap is exposed on this side and grab a’hold of it with your piston ring tool. Gentle squeeze whilst pushing toward the piston to clear the ring from its groove, then lift it straight up and off the piston. Relax your hand and there’s the compression ring laying in the tool.

DON’T MOVE IT. We want to keep it right-side up

Some rings are marked ‘TOP’ to give you the hint. (This set was.) Others have a dot or something to indicate this side up. And some don’t have a damn thing to go by. Which is why I don’t want you to alter the orientation of the ring.

You know you’re looking at the top of the thing because you’ve just removed it. Right now we don’t know if it was installed correctly or not but we’ll give them the benefit of the doubt. Inspect the ring near the gap. Ideally, there will be some kind of marking to indicate the top-side. If yes, then drop on down to the next step. If not, wipe the oil off the ring near the gap and use your pencil to make your own mark.

Now we know Which Way is Up, putting us ahead of at least 50% of the population :-)

NEXT STEP... is to examine the cross-section of the ring. Compression rings can take any shape and often do. Look for a step or angle on the inner edge of the upper ring. If you see something like that I want you to make a sketch of it. Doesn’t have to be artsy-fartsy just a simple drawing showing the shape of the compression ring relative to its orientation. (We already know which way is up, right? So that’s at the top of your drawing, meaning don’t do a Dali on me and drawn the damn thing upside down with a purple horse in the background. ) But keep it neat. Put the date on it, the engine’s serial number if it’s got one, and your name. Your printed name. This becomes part of the engine’s documentation package.

Once you know you can identify the compression ring, put it in the baggy with the #1 sticker and remove the second ring. Go through the same inspection, marking and identification process. Only difference here is that the Second Ring usually has an angle, groove or step on the outer face (and usually on the lower side, but not always.)

The bottom ring is the oil control ring and can take a wild variety of forms. Most recently, Mahle has been using a pair of thin oil-scraper rings separated by a corrugated steel band with color-coded ends. The oil scrapers can usually be installed any which way; most don’t have a preferred up or down so just remove them, then the corrugated band, and bag them.

With just three rings, you’re getting off easy :-) Some pistons have as many as six(!)

Finally, push out the wrist pin and add it to the contents of the baggy. Wrist pins are usually identical in weight to better tan a tenth of a gram.

- - - - - - - - - - - - -

Follow the procedure above for the remaining three pistons.


Got your scale? Okay, zero it then weigh each of the piston pins to confirm they all weigh the same. If your set of pins isn't identical in weight they you’ll have to make them so before going on. But 999 times out of 1000 they’re either identical or with 0.1g, which is small enough to ignore. If yours are not then drop me a line and I’ll lead you through the balance procedure.

With a clean pallet and clean piston, determine their weight. Write it on the top of the piston. After doing all four, re-set your zero and weigh them again, this time to confirm the first measurement. If the second weighing differs from the first, figure out what you’re doing wrong, correct it, erase the figures you’ve recorded and start over.

You should get something like this:

#1 = 386.4
#2 = 391.0
#3 = 389.1
#4 = 388.2

Subtract the smallest from the largest: 391.0 - 386.4 = 4.6 grams. A little over a quarter of an ounce; small enough to have the shade-tree types doing hand-stands. But if you’re a serious builder of good engines, it’s at least 4.5 grams too much.

With static mass-balancing the idea is to reduce the weight of the heavier parts to match the weight of the lightest part. That means you only have to balance three pistons, not four.

Start with the heaviest piston and remove metal from the edges of the skirt and from the balancing pads inside the skirt. Use a rotary file or a coarse flapper wheel. When you get to within 1 gram of your goal, switch to a fine flapper wheel. When you get to within a couple of tenths of your goal, wash the piston in white mineral spirits, blow it dry and confirm its weight. Remove the final fractions of a gram by hand using #600 wet & dry sand paper, smoothing the areas where you’ve already removed metal.

In the final stages, each time you weigh the piston you must make sure it is clean. The residue of metal you’re removed will try to cling to the piston. It will get into the ring grooves and wrist-pin trunnions. And when it does, its weight will still be there.

Balance all three of your heavy pistons. Try to hold to zero, plus or minus 0.1 gram.

After balancing, clean the pistons, re-insert their wrist pins and put them back into their original bags.

- - - - - - - - - - -

About the third or ninth engine you’ll start thinking there’s gotta be a better way to do this balancing shit. And there is, if you have a small lathe, meaning something with at least a 3" swing. What you do is rig a collar of soft copper to accept whatever size of piston you’re balancing then modify a boring bar to reach up under the piston’s skirt and remove metal from the balancing pads. Chuck the piston in the collar, zero the clock on your carriage (so you can determine your depth by thousandths of an inch), and start cutting. Ruining a few junked pistons will have told you how much weight you are removing for each 1/1000". To balance your jugs all you gotta do is watch the clock.

- - - - - - - - - - - - -

All sorts of people are going to tell you that balancing is a waste of time. These are usually the same folks trying to sell you over-priced un-balanced dune-buggy engines; the ones that rust-out before they wear out :-)

Some people want to balance their rods and pistons but don’t have a precision scale. A few have tried the simple balance-beam scale depicted in the ‘Idiot’s Guide’ only to discover there’s a bit more to it. Well... you can build yourself an accurate beam-balance but you have to be a pretty good metrologist to get repeatable results. So instead of shooting for the moon and missing why don’t you try to shooting for a goal you can achieve? Such as using one of those inexpensive gram-scales that are only accurate down to 2.0 grams. Okay, that’s twenty times worse than 0.1 gram but you’ll still end up with a better engine. Here; lemme show you why:

Weighing the same pistons above on a common postal scale having a resolution of two grams (about 1/8 of an ounce), I got the following:

#1 = 388
#2 = 392
#3 = 390
#4 = 388

At the very least you will be able to reduce your imbalance to the resolution of the scale, or 2.0 grams. The resulting engine won’t be perfect but it will be one hell of a lot better than one which hasn't been balanced.

Finally, there’s the guys who are afraid to modify anything. In that case, just weigh the damn pistons and think about it for a while. The VW engine is a ‘boxer’ design - - the crank-throws are paired. When cylinder #4 is at TDC it’s opposed twin, cylinder #2, is also at TDC (although on a different cycle). Clearly then you do not want to pair your heaviest piston opposite your lightest. If you installed work-number-1 in the #4 cylinder then you want to install the next heaviest piston in cylinder #2. That would be the work-number-3 piston (389.0 grams). So without doing anything at all you’ve managed to reduce the maximum imbalance for that PAIR from 4.6 grams to just 3.0 grams. The other pair comes out even better: just 1.8 grams between them. Here again, it isn’t perfect but it is better than trusting to luck.


Sunday, July 22, 2007

Basic Jugs - I

HEADZUP! The fins on your cast iron cylinder barrels are brittle. Drop one, the fins are going to snap off and you're gonna have to buy another set. So put down some cardboard. And be willing to sacrifice a toe if a jug gets away from you.

After-market VW jugs come in two basic flavors and a variety of sizes. The two flavors are A-types, meaning they're to be used with the stock crankshaft throw, and B-types for stroker cranks. A-types have a greater crown height; the distance between the center-line of the wrist-pin and the top of the piston. Stroker cranks shove the piston right out of the bore. By using a lower crown height the piston sits lower in the bore and will not protrude as far, meaning you can use a thinner spacer under the jug, your heads won't be pushed so far away from the center-line and your valve-train geometry won't be as badly out of whack. Of course, that also means the pistons will sit slightly deeper into the crankcase at BDC, where the piston's skirt may interfere with the flange of the opposing cylinder. So B-types also have shorter skirts in that area, although not short enough for a really aggressive stroker. As the Mechanic-in-Charge, part of your job will be to ensure there is no interference.


Today, buying pistons by mail order is a crap-shoot. To see why, go read...


When buying pistons what you wanna do is stand right there at the counter, open the carton and inspect the color-dots on the tops of the pistons. If all four don't match, don't buy. It's hard enough building a good engine with good parts; it's virtually impossible if you start with bad parts. And mis-matched jugs are bad, bad parts. (When you do find an honest dealer, buy as many sets of jugs as you can afford. [Figure 1] Good investment if nothing else. [I'm sad to announce that OVW will be closing its doors on 25 Dec 2007. Nancy will continue to accept drop-orders but the friendly little store with its honest and honorable people will be no more.])

But let's say you've found a suitable set of jugs, no broken fins (feel them), color-dots are okay like the set of Mahle's in Fig 2. (Yeah, they're cast. No, they'll do fine at propeller speeds.) The first thing you want to do is number them. Use a marking pen or crayon to put a big, bold number on the inner flap. This is called a work number; it doesn't have anything to do with the engine's method of designating cylinders. But the pistons are matched to your barrels and the rings are matched to your pistons. You can't let them get mixed up. And they will if you don't mark them. (See Fig 3)

Go find a container that will hold and protect four pistons. Turn on your air and rig a die-grinder with a narrow cut-off wheel. (No got? Then use a rat-tailed file.) Find your vibrating scriber and have it handy. (No scriber? Then get a round-nosed punch. [Make one out of a nail or something.] ) All tooled-up? Okay, pull a jug outta the carton and use a hammer-handle to push the piston out of the cylinder. Put the piston into the plastic bag and fold it over on itself; the next step calls for spraying abrasive grit around and we want to keep it off the piston. Find the flat section of fins and use the file or die-grinder to transfer the jug's work-number to the jug. It should look like Fig 4 when you get done (only prettier). That is, three notches means '#3,' one notch means '#1,' and so on. Before you put it back into the box, mark the piston. Herezhow:

Lookit the face of the piston. Find the arrow. That shows you which way the piston has to be installed on the engine. Turn the piston over and scribe the work number on the wrist-pin trunnion under the arrow. Herezwhy: If you're building a really good engine you're going to have your valve heads, combustion chambers and piston-tops treated with a ceramic-metallic thermal barrier coating. When the parts come out of the oven the coating will have obscured any markings on the crown of the piston -- you won't know which way to install the thing until you measure the off-set of the piston-pin. So you put your work-number on the trunnion that must point toward the flywheel-end of the crankshaft.

So... write the work-number onto the underside of the piston under the arrow, put it back into its plastic bag and put it into the second box you've provided. Now you can put the barrel back into the carton. (But there you are, die-grinder at hand, and you just know you could do a better job cleaning up the parting-line flash on those fins.... Don't. No air flows across the parting-line. [Think about it.] It doesn't matter if the fins are open or closed at that point. Grind on the things and you'll just be spraying lotsa abrasive grit around.)

Okay, got the gen? Then do the same procedure to the other three jugs and whistle when you're done; I'm gonna go cop a smoke.

You'll love this next step! A chance for you to exercise your artistry in paint. Herez whatcha need: Some flat black paint. If you don't have any, make some by mixing a tad of naptha with glossy black paint. If using Rustoleum Flat Black in the half-pint can as shown in the photo, you'll need to thin it with about an ounce of mineral spirits. But before opening the can, make sure it is at room temperature. Then shake it for at least two minutes. Don't guess; check a clock and give it an honest two-minute shake-up. Provide yourself with a stirring stick, open the can, add the mineral spirits and stir for at least one minute.

Obtain an inexpensive 1" paint brush; something cheap enough to throw away after using. (Why? Because it the cost of the mineral spirits needed to clean the brush is more than the price of a new brush. Using a pair of heavy shears cut off about two-thirds of the width of the bristles. You've now made a fin brush :-)

As you can see in the photos I've threaded the barrels onto a piece of extruded angle supported at both ends; a broom stick or piece of plastic pipe would work as well. Do not use anything that can scratch the barrels.

This particular set of pistons & cylinders was free of cosmoline. Some sets are not. If the jugs are greasy they must first be washed in solvent to remove the grease.

All set? Then go ahead and paint the cylinders. Try to keep the paint off of the machined surfaces. Use a paper towel dampened with mineral spirits to wipe off any mistakes; the machined surfaces must be perfectly free of paint when we assemble the engine. Removing it now is easier than removing it later.

It generally takes me about half an hour to paint a set of jugs. If this is your first set, you won't need that long. When you're done, wrap your paint brush in plastic and allow the paint to cure for about half an hour. Now take a strong flashlight and inspect your work for holidays. Surprise!

Okay, so it's a bit harder than it looks. (Which is why it takes me about half an hour.) Unwrap your paint brush, stir up the paint and do the job properly.

Once the jugs are painted it will take a day or two for them to dry sufficiently to be baked. Baking hardens the paint. It also causes it to shrink. If the paint is not fully dry, baking will cause the paint to crack, rust will form in the cracks and your engine will look like hell. And run hotter than it should, since rust makes a dandy insulator.

Another reason we must have a good paint job is because the next step in prepping our jugs is to give them a bath, complete with lots of scrubbing and a boiling water rinse. If you've missed a spot with your painting, your jugs are going to start to rust even before you get the engine assembled.


NOTE: You also need to check the length of the barrels within the set. All should be the same to within about .001" This may be checked with a surface gauge (ie, you don't have to actually measure the things -- just make sure they are all of equal height between the sealing surfaces). If the height is out by no more than .0015" you can live with it. Up to about .003" you can shorten the three longest cylinders. But any error greater than .003" is simply too much work; it would be best to find a more accurately made set. When checking for height measure at least three points of the circumference. You will occasionally find a barrel in which the sealing surfaces are not parallel to each other. If you have a shop full of equipment you can re-machine the barrel to make it square then adjust the length of the other barrels to match. But on the whole, you'll be miles ahead if you start with more accurtely made parts. -- rsh

Friday, July 20, 2007

Crankcase Painting

The Volkswagen crankcase is cast from a magnesium alloy (about 96% magnesium). A critical characteristic of magnesium is that it’s highly reactive; it likes to corrode. Upon manufacture the crankcase is usually treated to a chromate bath but the protection is defeated by time and heat.

Since a properly assembled engine based on VW after-market components can give twenty years or more of reliable service, it’s vital that the magnesium alloy crankcase be given some form of protection. For the home-builder, painting the crankcase has proven to be the most practical solution.

Although any good oil-based enamel will serve to protect the case, all forms of paint act as thermal insulators. To preserve the function of the crankcase as a thermal radiator a thin coat of flat-black paint will provide the best results, since flat black has a higher thermal emissivity than any other color.

If flat black paint is not available you may use gloss black. Mixing a small amount of naphtha or even gasoline (!) with the paint will kill the gloss.

Paints intended for high-temperature applications should be avoided. Often called ‘stove paint,’ barbecue’ paint or ‘exhaust’ paint and advertised as being able to withstand temperatures as high as 1200 degrees, these paints get their high-temperature qualities from clay, metallic salts or ceramic frits, all of which make excellent insulators. The use of such paints will reduce the engine's ability to rid itself of waste heat.

Common oil-based enamels can withstand temperatures up to about 400 degrees Fahrenheit, far higher than your normal crankcase temperature.

When painting the crankcase it’s important to keep the paint where it belongs, which is on the outside of the crankcase. This can be accomplished by careful brush-work. If using spray paint, you should mask any area you don’t want to paint. As a general rule that would include any sealing surface or threaded bore.

When building just a single engine the masking is usually done with tape. Threaded bores may also be protected with corks, plugs of various types and even dowels. However, people who normally build more than one engine at a time often make up a set of re-usable masks. Some of these can be quite elaborate but I've found cardboard to work well enough.

In Fig 3 you can see the front of the crankcase with the cam plug and the #1 main bearing area masked off with cardboard salvaged from a cereal box (I think :-). Dowels are used to mask the tapped holes to the lifter oil galleries while the main oil gallery has been sealed with a small cork.

The cardboard is held in place by rubber cement. Applied to the cardboard and allowed to dry, it remains tacky enough to stick to a clean crankcase, peeling away without leaving any residue after the paint has dried.

Whenever possible I try to use an existing part or gasket for the mask. In Figures 4 & 5 you can see the anti-splash baffle being used to mask the dynamo base while an old sump plate takes care of masking the bottom. Fig 4 shows a couple of corks and another dowel. Normally, I use an old distributor body and a fuel-pump block-off plate as masks but they've wandered off so I used masking tape.

The crankcase shown here was painted with Rustoleum Flat-Black in a rattle-can, which makes it rather expensive. An air brush works equally well and a quart of paint will do a dozen engines or more.

At my location it takes the paint about a day to cure well enough for it to go into the oven, where it will be baked at 170 degrees for four hours, after which it's remarkably bullet-proof. If you don't have a shop oven that will accept a crankcase you can line a cardboard box with aluminum foil large enough to fit down over the engine and rig a 100W incandescent lamp to go under it. The rising heat will be trapped by the box, raising the temperature high enough to harden the paint in about 12 hours.

If you live in a warm, sunny climate you can also pop the painted crankcase into a parked car standing in the sun. It generally takes two or three days for the paint to achieve the hardness and scratch-resistance it gets from being oven-baked for four hours. (Even a black car will reach thermal equilibrium at about 145 degrees F, a bit low for optimum paint-curing.) But be warned: As the paint cures a greasy residue will appear on the inside of your car's windows :-)


Wednesday, July 18, 2007

Crank Basics - V

Bagged and swaddled, the crank shown in Fig 1 gets laid gently in the back of my 1965 VW bus and we putter off toward Escondido. Traffic on Highway 78 is moderate so the eleven mile trip takes only twenty minutes with just two sessions of stop-&-go. The old bus has no trouble keeping up with the 300hp punkin seeds darting from lane to lane looking for what doesn't exist. Highway 78 is a linear parking lot about twelve hours out of 24, virtually empty the other twelve.

Don at HDS looks the crank over, we discuss the job, he writes me out a ticket and I'm free to return to the six-lane insanity. Barely an hour after leaving the house, I'm back.

As you can see from the photo the crank was delivered fully mantled save for the bearings. On one end of the crankshaft is the propeller flange and spool from Great Planes, on the other is the Harley Davidson permanent magnet dynamo, installed on a hub of my own design and manufacture. Drawings of the rotor hub and the stator mount will be posted to the Chuggers Group when I get around to it but previous posts will give you a hint as to what it looks like.

No one answers the phone in southern California any more. We live in what has become an up-scale ZIP code, targeted by politicians, telemarketers and evangelists to the tune of two dozen calls a day. We spin through the messages every evening and after a couple of days HDS leaves a message saying the crank is ready for pick-up.

This time I take surface streets. It's a few miles farther but takes less time.

The job-ticket is translated into a bill which I take to the office for payment. The yellow receipt is the crank's Ticket of Leave and Don haul's it out to the bus for me because it's kinda oily and I'm wearing a spiffy Hawaiian shirt. We chat for a bit, discussing the rattle from the spacer and the fact the assemblage was relatively clean, meaning he didn't have to do much work to remove the wobble. In fact, on the first run-up it was within spec for a stock VW crankshaft (8 gm/cm ) which he reduced to about .1 gm/cm. Once it's mounted in the airframe I'll go through the same procedure with the prop. No one ever believes how much this benefits the power-plant until they actually do it.

"Nice shirt," he sez, pretending to go blind. I've known him about twenty years; have three more crankshafts coming his way. I'll wear one of my really gaudy ones next time.

Back home via Stagecoach Road and Twin Oaks Valley, I lug the crank into the shop and start writing on it. The crank has survived its Rite of Passage. It is no longer just a crankshaft, it is part of an engine, serial number HVX0381, which I scribe onto one of the flanges with a carbide burr. I get one of the little red Engine Logs from the cupboard and start filling in the blanks. The log book will go into a big zip-loc along with the other documentation. Now I get to take the sucker apart for the second time, the first having been to trial-fit the main bearings, during which I also clocked the case to determine what size cam-gear I'll need. Fitting the cam-gears is one of those unimportant details the shade-tree types like to ignore.

Due to normal tool wear and tolerances, the distance (and sometimes the alignment) between the crankshaft and the camshaft varies slightly. The difference is small but significant, since it involves a gear-train. To accommodate the differences Volkswagen used nine different sizes of cam gears, from a -4 thru zero to a +4. They started out with just four sizes; -1, 0, +1 and +2. But factory-overhauled engines often required align-boring, which lead to the other sizes. The markings are on the inner face of the cam gear so as not be confused with the o used for the timing alignment.

The Factory Manual will tell you what checks to perform to see if you've got the proper cam gear. Or you can read all about in my two-part article "Dialing in Your Cam" that appeared in the 2001 October and November issues of 'VW Trends' magazine. (Sure to be a collector's item :-)

But right now I was busy taking the crank apart and writing, etching or stamping '0381' on all the bits & pieces. Well.... most of them, anyway.

In Fig 2 you can see how little metal Don had to remove to achieve zero wobble. (There's a matching patch on the opposite end of the crank, on the other side.) Grinding away that amount of metal meant the crankshaft had to be fully dismantled, all the plugs pulled then cleaned to within an inch of its life. Or whatever. I used lacquer thinner in a wash-bottle as my solvent, plus a variety of brushes, one of which you see in the photo.

After being scrubbed and scoured the crank gets blown dry then undergoes a visual inspection, where you poke a grain-of-wheat lamp on a wand into this hole here whilst peering down that hole there to make sure there's nothing in the hole but hole.

Then you get to put it back together again, only this time with bearings.

Since this crankshaft is counterweighted it has about four more pounds of flanges than a stock crank. When balancing a flywheel or stock crankshaft the usual method of removing metal is to drill it out. That isn't always possible with a counterweighted crankshaft because the outer portion of the flanges is fairly thin, which is why the metal is removed by grinding instead of drilling. Figures 3 is the 1/3 flange of a new stock 69mm crankshaft that has been factory balanced, (Meaning it's 'way the hell out of balance by modern-day standards.) Fig 4 is the 2/4 flange on the opposite side. Such divots are the balancer's spoor, telling you that particular component has been balanced to... some standard or other. The stock crank is destined for a 1968 bug. It will be presented to the balancer wearing a flywheel & clutch cover on one end, all of its gears, and a stock steel fan-belt pulley on the other. It will then be balanced as a complete assembly and to modern-day standards. In return, the engine will typically produce about 10% more power for the same amount of fuel.

This article marks the end of the series on crankshafts. I'll probably cover installation of the rods using a different engine. Right now, I want to complete work on the crankcase and start prepping the jugs. And there's still a pair of heads waiting to be prepped. (Good thing I got all this time on my hands :-)