Sunday, November 26, 2006

AV - Distributorless Ignition System


"DIS" stands for 'Distributor-less Ignition System,' of which the Compu-fire DIS-IX is a good example. Which causes a lot of non-mechanics to start jumping up & down, pointing at the body of the Bosch -009 distributor and insisting Compu-fire should be sued for false advertising.

The problem here has to do more with language than automotive engineering.

On the Volkswagen engine (and all other cars of its era) the device we commonly refer to as a 'distributor' fulfills three roles, only one of which has anything to do with distributing the spark from the coil to the proper plug. That chore is accomplished using a high-voltage rotary switch, a special cap having terminals for the spark plug wires and a graphite button against which the rotary switch presses, and the high voltage leads connected to the spark plugs, as well as the lead between the coil and the distributor cap.

Due to erosion of the high-voltage rotor, wear of the center contact and break-down of the cap's dielectric over time, the distribution function requires frequent periodic maintenance. When we do away with the distribution function we automatically eliminate the need for a significant amount of maintenance which increases the inherent reliability of the ignition system. That is why all modern engines use some form of distributorless ignition system. A good example of this is modern-day automobile engines that can go 100,000 miles without a tune-up.

The two other functions performed by the thing we call a distributor are ignition switching and ignition timing. Ignition-switching is just that: a switch that turns the system on and off. Historically, this chore was handled by a mechanical switch having tungsten-alloy contacts commonly called points having a service life between 100 and 500 hours. In modern-day systems the points have been replaced with a transistorized switch, typically having a service-life in excess of 5,000 hours.

The final task of the thing we call a distributor was timing: telling the points or transistor when to turn itself on and off. The nature of the Otto-cycle engine is quite critical to ignition timing since the precise moment of ignition varies according to the speed of the engine. Why this is so has to do with the fact that the process of combustion takes approximately the same amount of time regardless of the speed of the engine, forcing us to light the fire a bit earlier as the speed of the engine increases.

With the Compu-Fire DIS-IX ignition system the distribution function has been eliminated, replaced by a pair of two-cylinder waste-spark ignition systems. Ditto for the switching function, which is now accomplished by a pair of high-powered transistorized switches. But we still have need for the timing function and the body of a Bosch -009 'distributor' contains a robust centrifugal-advance mechanism that fulfills that role in a practical, inexpensive and reliable manner.


It's worth noting that every magneto contains a 'distributor.' Magnetos continue to use the same arrangement of a mechanical rotary switch to distribute the spark voltage to the spark plugs as found in automobile distributors. In doing so, the magneto is subject to exactly the same ills which plague automobile distributors and require the same type of periodic maintenance. Inside the magneto you will also find a set of ignition points and a 'condenser,' functionally identical to similar components found in the ignition systems of older automobiles, susceptable to the same wear and requiring the same maintenance.

The typical magneto used on Volkswagen conversions presently costs about a thousand dollars, has a service life of about 500 hours, and requires a special mount. The DIS-IX system costs less than three hundred dollars, plugs right in to the VW engine and has a useful life conservatively rated at fifteen hundred hours. But even more important is the fact it is easier to start and provides a better spark than the typical magneto.

To install the DIS-IX system, remove the distributor cap, rotor and points from your -009 distributor and toss them. Replace the rotor with the DIS-IX magnetic disk then attach the DIS-IX cap. The 'brick' of two coils can be mounted on the firewall. When properly mounted and wired, the DIS-IX allows even the largest VW conversion to be started with a flip of the prop.

SOP when using this unit in an airplane is to install the grub-screw mod, locking the distributor body in place, and to safety-wire the clips securing the cap to the distributor body. These items have been discussed in most of the Groups devoted to VW-powered aircraft and the mods have even been illustrated on some of them.


VW - Annealing Copper Washers

>I was thinking that a while back someone said that you can take the copper >washers and heat them with a torch till they are red hot and then let them >cool and you can reuse them. The heating returns their flexibility.


You heard wrong. On two counts.

Heating copper then flicking it into cold water is how you anneal it; make it softer.

But part of the problem is that the washers have been crushed -- their thickness has been reduced. Annealing them does not make them thicker.

The VW sump plate was secured with acorn nuts. Their purpose was to limit how far the nut can be threaded onto the stud. With undistorted parts, meaning they should be flat, and gaskets of the proper thickness and composition, meaning they should be impregnated paper rather than plain cardboard, and a copper washer of the proper thickness and temper, putting it all together and torqued to the proper spec ( 5 ft-lbs ) gave you a leak-free fit automatically.

That was then.

Over time, the acorn nuts vanished, replaced with a common nut installed with an un-specified amount of torque, which made the thickness and temper of the copper washers even more critical than before.

drip drip drip...

-Bob Hoover

VW - Leaky Valve Covers


>My vales covers have started to bleed on me and I'm gonna be replacing the >gaskets here shortly. My question is, what can I do to make sure there won't >be any leakage when I put on the new gaskets? Is there a gasket glue I can >use or something olong those lines, how bout doubling up the gaskets?

With the valve cover perfectly clean, attach the new gasket to the valve cover using any common gasket cement (Permatex, Indian-head, etc).

Do not attempt to use two gaskets. A second gasket will not fit. The system works perfectly well with just one.

There are three principle causes for leaky valve covers, two of which are obvious and one that is not.

The two obvious causes are: (1) Age and heat causing the gasket to become compressed and hard so that it no longer forms a seal, and (2) The gasket gets out of position, either because the gasket is not properly glued to the valve cover, the wrong valve cover is used or casting flash on the head prevents the valve cover from seating properly.

The less obvious reason has to do with the sealing surface around the valve gallery -- the surface against which the gasket is pressed to form the seal. IF this surface becomes scratched or dinged -- even slightly -- it will not form an oil-tight seal. These scratches and dings usually occur when we adjust the valves.

If the sealing surface is not perfectly smooth, make it so, using a mill-cut file and #320 or finer sandpaper.

The edges of this sealing surface should have slight chamfer (1/32" or less).

The typical veeduber ignores this accumulation of tiny scratches and dings because it's 'obvious' such minor things can't cause an oil leak :-)

Properly assembled, the VW engine leaks no more oil than its water-cooled cousins.

-Bob Hoover
-Feb 1999

VW - Heat Risers & Education

Frustrated in Indiana wrote:
>No matter what I do I cannot get both sides of my preheat tubes to heat
>to the same level. The passenger side gets very hot while the drivers
>side gets only lukewarm. I was told that this was not a problem.
>Anyone who knows different, please let me know. The preheat tubes do
>not connect correct???????


Dear Frustrated,

Yes, they do connect. But you may not have a problem. The heat-riser gives up its heat to the manifold in order to ensure proper vaporization of the fuel. That means one side should be cooler than the other.

The manifold pre-heat pipe is in fact one pipe about four feet long(!) that runs from one of your exhaust stacks to the tailpipe of your stock muffler. That puts the inlet at in a zone of high pressure (ie, the exhaust stack) and the outlet in an area of low pressure (ie, the peashooter on the driver's side of the muffler).

The pressure differential is important because the hot exhaust gases give up their heat to the center section of the intake manifold casting (ie, where gasoline absorbs the heat and changes its state from an atomized liquid to a true vapor). Once the exhaust gases have given up most of their heat, you must have that pressure differential to insure adequate gas-flow through the pipe.

Fail to pay attention to those fundamental rules of physics and the system won't work.

And as you may have noticed, virtually all of those kewl after-market exhaust systems ignore those fundamental rules.

What you get with those oh-so-kewl after-market exhaust systems is an inlet on one exhaust stack... and the outlet on another exhaust stack. Which guarantees the system won't work.

Why not? Because you are trying to dump from a high pressure area to a high pressure area. Instead of a manifold heater, you end up with a fluidic yo-yo. And a hole in your wallet. And a VW that doesn't run very well.


When exhaust gases are cooled they can no longer support a host of combustion products. The combustion products, from water to soot to metallic compounds, are deposited on the walls of the exhaust system plumbing. When the plumbing is small, such as the manifold heater pipe, the combustion products will eventually block the pipe.

"Eventually" can be up to a 100,000 miles on an engine with a stock exhaust system or as little as thirty minutes (!) with one of those kewl after-market systems and their fluidic yo-yo.


If you thought all that was a gas, you'll love what comes next :-)

So the kiddie installs one of those go-fast/make-noise exhaust systems that all the magazines say are really, really kewl and worth at least 10hp, mebbe more... and the kid quickly discovers his ride runs like shit. Of course, it can't be the really, really kewl exhaust system so it hasta be that stock distributor or the carb or the fact that as a mechanic the kid would make a fine janitor and hasn't cracked a book since sixth grade, when he learned how to type and now learns everything he needs to know via the internet, including how to fix his ride :-)

The 'fix', according to all the instant experts, is to install a really kewl 009 dizzy and a set of Kadrons, complete with failure prone linkage and cheese cloth air-cleaners. And sure enough, the thing now runs at least as well as it did before, mebbe even better. Of course, he's now spent about $500 ( which is what all those instant experts really cared about). And with those grossly deficient air-cleaners, mechanical advance distributor and those rich-running Kabrons, the service-life of his engine just took a header into the porcelain fixture, which is also counted as a Big Win by all those instant experts drooling to sell him a new engine and all the neet stuff to go on it.


If you've got a stock exhaust system and aren't getting an adequate amount of heat to the manifold, drop the engine, pull the manifold and clean the heat-riser.

If you've got an after-market exhaust system, chances are the heat riser flanges are simply tacked on to the exhaust stacks, which guarantees the heat riser pipe will clog up.

Back in the sixties EMPI offered a header-type exhaust system that really worked. It carried the heat-riser outlet all the way to the 4-into-1 collector. Worked great.

If you run a center-mounted carb on a horizontally-opposed engine you need supplemental heat to insure proper vaporization in the runners. No mystery to any of this, it's in all the books and has been for seventy years.


But I saved the best for last :-)

Virtually all of those really-really kewl after-market exhaust systems address only two of your four cylinders. So long as you run the stock heat exchangers, all you've done is upset the volumetric balance of the engine.

Wanna go-fast/make-noise? Pull your peashooters and install a zoom-toobe. Most of the restriction in the stock system is in the peashooters, the big canister is just an expansion chamber. Get rid of the peashooters and you'll have about the same reduction in back pressure as you get from installing an 'extractor' on only two of your cylinders... but without upsetting the volumetric balance or causing the heat riser to clot shut.


I'll leave you guys to figure out why you don't see these unimportant details mentioned in the magazines :-)


> What is your reccommended method for opening a plugged pre-heat tube? >Nasty chemicals? The old ex-clutch-cable-in-the-drill trick? The >oxy-assisted burn it out>


You let out 'None of the Above' :-)

The fastest method is to use media blasting and a flexible wand.

I know St. Muir sez to use oxy-assisted burnout but take it from me, never use oxygen-blast. You'll melt the aluminum jacket that bonds the manifold to the heat riser long before you burn away the deposits inside the heat riser. (This is another example of the many destructive errors in the Muir book.)

Oxy assisted burnout works fine with cast iron manifolds and was the standard procedure for Model A's and V8 Fords but it simply does not work on the VW intake manifold. Why? Because by the time you raise the heat-riser pipe to the required red heat, the aluminum jacket will have long since melted away.

Soak & Poke (ie, carb cleaner and spinning a cable inside the pipe) works but is slow and messy. And it doesn't have to be a clutch cable. E-brake cable will work... as will any multi-strand steel cable. Just rotate the cable in the direction opposite of the lay and the end will 'fluff up', make a pretty good brush.


>I never cease to be amazed at the things that I never thought about. Thanks, Bob!


You're welcome.

For me, one of the most rewarding aspects of veedub-dom is reading all those neat reasons the kiddies use to support their totally invalid conclusions, such as how much better their ride handles now that they've dropped it nine inches and increased the caster angle to sixteen degrees :-)

A favorite is the 'fweem' crowd :-)

Block off the heat riser and guess what happens to that 'fweem' sound :-) or, for the serious experimenter, work that equation backwards and figure out where that 'fweem' sound comes from.

It's really unfortunate that so many present-day owners of aircooled Volkswagens never had the opportunity to drive one out the showroom door. Today, most veedubs are rolling wrecks and their owners don't even know it. They've never driven the Real Thing, have no idea how well the VW can handle, how reliable and economical it can be. And they never will, thanks to all the swell advice they get from instant experts who will do literally anything to sell their junk to mechanically naive youngsters, even if it means destroying the vehicle or risking the kid's life. (Go on kid, tear them flaps outta there! Then lemme show you how to lower that thing :-)


>So where should I, new to VW's, be looking for info? I've got pretty
>good sense, am mechanically competent, and am willing to learn. I've got
>a a copy of Muir, and the Bentley for my '70 transporter is on the way.
>Any suggestions on where to get more, reliable info?


You've asked a good question, not just about Volkswagens but about life in general. Unfortunately, there is no pat answer.

The generic answer is that the answers to all questions will be found within yourself. You gather information, use it to formulate what appears to be the most correct answer and then test your conclusion against reality.

In effect, the answer will reflect your perceptions. The problem is, in modern-day America, the typical youngster does not understand this extremely important learning process.

At one time all youngsters were exposed to the elements of logical reasoning in the public schools, usually between the ages of 11 and 13. This provided the foundation that allowed them to acquire knowledge from information, rather than simply memorizing the material and vomiting it back up during Finals. Mastery of Logical Reasoning (under various names) was the Rite of Passage between Primary schooling, which was devoted mostly to rote memorization, and High school, in which the student was expected to actually learn something.

Nowadays the process of learning by rote extends even to our colleges and the fact that a parrot is not a scholar is politely ignored.


As to your specific question, the best source of information is the Volkswagen Workshop Manual. The 'official' manual sold by Bentley is an abridgement and has omitted a great deal of vital information.

Muir is a good means of demystifying the automotive arts but it is larded with factual errors.

The Haynes manual for the bug and Ghia (Haynes #159) is probably the most cost effective source of VW information for the beginner.

If you intend to overhaul your engine you should hold a copy of Tom Wilson's "How to Overhaul Your Volkswagen Air-Cooled Engine"

For some insight into gaining more performance from a VW engine you should study Bill Fisher's "How to Hotrod VW Engines". For body work, painting and so forth there are other very useful manuals, some of which I've mentioned in previous articles.

If you are a rank beginner your best bet is to start with lawnmower engines(!) They are small and you can usually get all you want for free, simply by running an ad saying you'll haul the thing away. You will need the Briggs & Stratton handbook or some similar tome (Haynes offers one) and a few tools.

People who don't understand automotive engineering often laugh when I suggest they start with smaller engines but an air-cooled one-lunger has about 85% of the 'DNA' of your VW engine... or your Pratt-Whitney, Lycoming or what-have-you. They use the same Otto-cycle, the same poppet valves, the same cam/crank relationship, the same principles of ignition, carburetion, intake and exhaust. These things are the foundation you need if you want to be able to maintain your veedub.

Once you've mastered the basics, be it engines or suspension systems, you will have established the framework of knowledge that will allow you to understand and appreciate the differences between, say, a lawnmower engine and a Corvair engine.... or a Volkswagen engine... or any other air-cooled engine. I know that sounds a bit fey but in engineering terms, the differences are merely matters of detail rather than principle. The most significant gulf is not between a 4,000cid aircraft engine and a VW but between liquid- and air-cooled engines, in that air cooled engines operate at significantly higher temperatures and their maximum sustainable output is determined by their fin area.


As for my comment about driving the 'Real Thing,' it was not a joke. Most Volkswagens that I see suffer from some horrendous problems of which the owner is not even aware. But by the time I see them the accumulation of such problems have reached the point where it would be economically impossible for the typical VW owner to have the vehicle returned to spec. For the very wealthy, it's not a problem to cough up seventy bucks an hour for a hundred or more hours of skilled labor. They come away with an antique bug or Ghia that is literally in better-than-new condition. But for the average owner the only option is to do the work themselves and the record shows most are unwilling or unable to do so.


The real problem with cleaning the heat riser is when it's completely blocked. All of the usual methods work best when the pipe is still partially open. Once it becomes blocked your chemicals can only work on the end of the plug, a relatively small area. Your cable-brush is most effective scrubbing the wall of the tube rather than boring a hole through a solid plug.

And finally, the tube isn't round. Under the aluminum casting, where the two pipes are siamesed together, the heat riser is crushed down to a D-shape. This insures the largest possible contact area between the pipes but the D-shape prevents any brush from getting into the 'corners'. And if you don't get the pipe really clean, the residue will act as a 'seed', attracting combustion products and quickly clogging up again.

Media blasting works better than any of the other methods.

Vinyl or rubber tubing works fine as the applicator wand. Once you break through the plug it takes only a few minutes to scour the pipe clean.

But don't use heat. And don't remove nuts with a chisel. The fact a procedure is valid for a steam engine or a Model T doesn't mean it can be applied to a Volkswagen :-)

-Bob Hoover

VW - Battery Notes

My wife and I are amateur astronomers. In 1991 we journeyed to the tip of Baja California to spend seven minutes and forty-two seconds standing in the shadow of the moon. As total solars go, this was the E-Ticket ride of the century but what made it even more unique was the ability to drive to the location of maximum totality. Our planet is mostly water and the majority of long-duration total solar eclipses are only visible from a boat, too expensive for us amateurs. Most folks guessed there would be at least a hundred thousand people willing to drive down to Baja to experience such an event. Some estimated as high as a million since it's such an easy trip, which is why we decided to leave early.

Seeing as we expected to be away for a full month and in the middle of summer below the Tropic of Cancer, we took the camper I'd built onto my old Datsun pickup. It has a toilet, shower, swamp cooler and all the stuff girls consider necessary for roughing it.

We had a good time. Saw a couple of painted caves that aren't on the maps, did a lot of fishing, beachcombing, surfing and so on. Then came the eclipse. Too spectacular for words; you really had to be there. But a bit of an embarrassment, interest-wise. Best estimate is that less than 5,000 people showed up and the majority of those were from Europe, Asia and Canada.

When we got home, my bus was dead. Or rather, it's battery was. So I bought a new one. I usually don't. Usually, I hit the junk yards and buy a battery out of a wrecked new car. Usta cost five or ten dollars. More now, of course. But when I went looking I couldn't find any big batteries. And I mean big, like you find in an air conditioned Coupe de Ville. Lotsa little batteries but I wanted a Type 27. Couldn't find one at the junkies so I had to buy one. Delco ‘Voyager' 105 A/hr deep-cycle, marine battery, yada yada yada. Cost the earth.

I run two batteries in the bus, one for the engine and an auxiliary for everything else. I had an old Exide Type 27 as the auxiliary but it was more than ten years old and I figured it wouldn't do for the engine. So I bought the big Delco and installed it in August of ‘91. (The Exide crapped out in 1998 and was replaced with a Type 24 from the junk yard.)

The Delco finally gave up the ghost.

The Delco was one of those low-maintenance types, the kind you have to chisel off the caps to re-fill with water, which I did every couple of years. But last week it wouldn't start the bus. Checking it out, I found a shorted cell. And only eleven years old, too.

I transferred the auxiliary into the engine compartment to get the thing running. Last week I visited the junkies but as before, all I found were little batteries. Finally said to hell with it and bought one. Couldn't find a good one. Wal-Mart and Price Club appear to have driven the local battery shops out of business. Ended up buying one from Costco.

A Type 27 won't fit in the battery space of a 1965 VW bus. It hits the tail light. ‘Way back when, I built a new battery tray that raised the battery about four inches. The forward part of the tray is the after part of the rear wheel well and raising it up allows the battery to sit farther forward. The auxiliary battery is just forward of the same wheel well but inside the cargo bay. It's in a box and most folks never even notice it but when you camp, that's what's powering the lights and computers and radios and stuff. I use a pair of relays to isolate the batteries. (If you're using one of those diode isolators, don't. The voltage drop across the diodes guarantees the batteries will never be fully charged and with a lead-acid battery, 50% of the charge is in the top couple of volts. Use locally available relays to duplicate the circuit used in Westys and the better RV's.)

Raising the battery up in that manner, which is only possible on a bus, makes it inconvenient to service since you have to remove the battery to check the water and you have to remove the air filter before you can remove the battery. Since I pull the engine every couple of years, it isn't that big a deal, plus it makes for a neat installation; there's never any corrosion to worry about and the space under the battery tray is large enough to hold two spare quarts of oil without them rattling around.

I wish I could have found a name-brand battery. I've found they last eight to ten years if you take care of them. Although house-brands are usually built by the same companies their quality tends to be lower because they cut a lot of corners in to keep the price down, which you can discover for yourself by simply taking a few batteries apart. (I recycle the acid then neutralize the plates and melt them down for the lead, which I mold into bullets.)

So howz your battery doing?

-Bob Hoover
-Dec 16 2002

VW - Manifold vs Carburetor Vacuum


Recently I've seen a couple of posts where people have gotten manifold pressure and the carburetor's vacuum advance signal confused.

The two are both 'vacuum' but they aren't directly related. The signal used to control the distributor's advance is a reflection of the rate of air flow through the venturi of the carb. The more rpm, the wider the throttle, the stronger the signal.

Manifold pressure is created by the cylinders on their intake stroke, sucking air out of the manifold. At maximum rpm, with the throttle wide open, manifold pressure will approach atmospheric pressure (ie, virtually no 'vacuum' at all). But since the rate of flow through the venturi is now at its max, so too is the venturi-generated vacuum-advance signal.

No mystery here. It's in all the books.

For those who never understood the principle of vacuum advance to begin with, the matter gets even more confusing when they encounter a dual-canister distributor, which uses manifold pressure (ie, vacuum) to return the advance plate to its static timing point any time the throttle is closed, either immediately or after some small delay as determined by a control valve. (This is a smog control measure, intended to promote better combustion during the lean-out/deceleration that occurs when you lift your foot off the accelerator pedal.)

The basic reason for using vacuum advance for ignition is it's greater sensitivity to changes in the load placed on the engine, which are accurately reflected by the rate of air flow through the carb. Centrifugal advance mechanisms offer a wider dynamic range than vacuum advance systems since the amount of total advance and the rate of advancement may be 'programmed' by adjusting the mass of the bob-weights & springs. In the late 1920's Remy (later Delco-Remy) developed a composite advance mechanism combining the sensitivity of vacuum sensing to initiate the timing's advance, with a centrifugal mechanism to sustain the advance, having found such a system provided better driveability.

-Bob Hoover
-Mar 2001

VW - Valves, Guides and Seals


Back when I was young and the world was gay... or maybe that should be the other way ‘round... No, that sounds even worse. Lemme start over.

Back when I was a kid in Modesto, California there was a delightfully perverse young lady who could suck a golf ball through a fifty foot garden hose. She occupies a special place among my memories because she taught me a lot about auto mechanics. Or rather, she caused me to learn a lot about auto mechanics. She lurched into Hendy's Drive-In in her 1937 Ford tudor, said it was running like shit and offered to demonstrate her remarkable talent for anyone who could fix it, pronto. The car immediately vanished under a dog-pile of hot-rodders oozing testosterone. Half an hour later the car was still there. It would idle okay but began bucking and wheezing whenever the throttle was touched. The hot-rodders had vanished; the prize unwon.

I strolled over as she was latching the hood (it folded up from either side), nudged her aside, pulled the air cleaner, played the choke & throttle together to get the revs up to about 2500 rpm, then mashed my hand over the throat of the carb, which just about did to me what she could do to a golf ball.

Didn't help. So I did it again. The third time I gave it the Po' Boy Carb Clean, it cleared whatever had been blocking the high-speed circuit, settled down and ran like a top. I put the air cleaner back on, latched the hood and strolled away, the epitome of Mr. Cool, right down to my blue suede shoes.

Actually, it was pure dumb luck. The hot-rodders were convinced she had a problem with her ignition and gave the car a quick tune-up while I watched. By the time they were done it was pretty obvious the problem had to do with a lack of fuel at high speed, which everyone assumed was due to a bad fuel pump or a dirty carb and since neither could be repaired pronto, they gave up.

Truth is, I didn't know what marvelous things occurred when you revved an engine then shut off the air with your hand. But over at the VW dealership where I worked I'd seen one of the mechanics do it for a beetle with the same symptoms and it seemed worth a shot. It wasn't until later, when the grateful young lady was fulfilling her promise, that I experienced a suction-related epiphany.

Manifold Pressure That Isn't

Your engine is an air pump, right? (Auto Shop 101. Which happens to be wrong but there it is.) Rev the engine, it's gotta suck some air. Close the throttle, the engine can pull a pretty good vacuum before it slows down. If you can somehow extend that suction to above the throttle plate -- to include the entire carburetor -- it will occasionally clear a clogged jet or bleeder port. To accomplish that, simply clap your hand over the inlet to the carb.

The suction is the result of the pistons descending in their cylinders with the intake valve open during what is called, oddly enough, the Intake Cycle. (For your Pop Quiz, during which cycle does the piston descend with the intake valve CLOSED?). The amount of suction is always greatest when the throttle is closed or nearly so, which occurs at idle or whenever you suddenly lift your foot from the accelerator.

We tend to think of the suction occurring only in the intake manifold; that its only role in life is to suck some gas out of the carb. We tend to forget that the vacuum is present everywhere in the system, from the top of the carb right through to the top of the piston down inside the cylinder.

It's the presence of that vacuum that causes oil to be drawn into the combustion chamber. If your rings and valve guides are in good shape the amount of oil drawn into the chamber is small but there's always some; if your rings or valve guides are worn - and if the guides are not fitted with seals -- the suction can pull a copious amount of oil into the cylinder. That's what causes you to blow white smoke out the tail pipe, fail your smog test and stink up the neighborhood.

(Didja notice the or? )

Rings or guides. We tend to say ‘valves' instead of guides but in fact, the valve's stem is steel whereas the guide is putty-soft aluminum-phosphor-bronze. After thirty thousand miles we can expect the valve's stem to be a little bit worn but most of the wear appears in the softer guides. (See 'Wiggle-Wiggle.' Or the factory service manual. The 'wiggle' test is a standard procedure for all OHV engines.)

With aircooled Volkswagens it's important to make the distinction between valve guide wear and piston ring wear because the guides wear-out about four times faster than the rings. Fail your smog test because of elevated hydrocarbon readings but still show about 125 on a compression test? You've got worn valve guides, pard. (Oil is a hydrocarbon too.)

Since the valves don't show much wear, a lot of folks reuse them. Bad, bad idea. You can regrind & reuse the intake valves... mebbe once. But you should always replace the exhaust valves. That's because the exhaust-valve ‘wear' you really have to worry about has to do with metallurgy, not the dimensions. After thirty to fifty thousand miles of use your exhaust valves are liable to suffer metal fatigue and snap off just behind the head. Saving a few bucks by reusing the exhaust valves can cost you the price of a new engine. Some bargain, eh?

Juicy Rockers

Veedubs don't have a very good lubrication system. All the oil to the right-hand side of the engine gets there via that tiny little channel behind the #2 cam bearing. Everyone who has rebuilt more than a few veedubs has seen the galling on the underside of the rocker-arm shaft, inside the rocker arms themselves, and the wear marks on the washers & rocker-shaft towers. After a few dozen engines you learn to reverse the rocker shaft and swap it from left to right in an effort to equal out the wear. But about the third time you have a hair pin snap, you figure there's gotta be a better way and you start fooling with the lubrication system. Most guys raise the pressure by stretching the spring. That helped a little. But if you modified those war-surplus Wisconsin jugs to fit your 36hp engine, with your home-made dual-carb manifold and three pound flywheel, soz you could keep up with the Model A's all the other kids were running, you quickly discovered that more power meant more heat and more heat made the lack of adequate lubrication even worse.

(Work with me here. I'm talking 1956.)

Turns out, there's a whole buncha things you can do to get more juice up to your rockers. And juicy rockers don't gall. Nor does the hair-pin snap. And all that extra juice out in the valve gallery picks ups a shit-load of extra heat and that means your dinky 7mm valves stop wearing at such a furious rate. (Ed.Note: Early valves had 7mm stems.)

So you do all that stuff. And end up with a reliable little screamer that will flat eat a Speedster and life is good. Except for that huge cloud of white smoke that seems to follow wherever you go.

Speedster For Lunch?

The basic VW engine design dates from the early 1930's. Unfortunately, it stayed that way for the next fifty years :-) But not in the hands of American hot-rodders. From the mid-1950's there has been a steady flow of race-proven modifications applied to the VW engine. The most effective modifications are surprisingly simple and while they are common knowledge to all competent engine builders, the odds are you've probably never heard of them. They've never appeared in any of the magazines that I know of, probably because there's nothing to sell - the mods are made when you build the engine. Nor were they applied to street machines because the lack of effective valve stem seals guaranteed you'd flunk your smog check.

That was then.

Nowadays effective valve stem seals are commonly available. They don't happen to fit stock Type I valve guides but in the file of illustrations (linked below) I've shown you a couple of ways around that.

Valve Stem Seals

If the engine is running, there's a vacuum in the intake manifold. Wide open throttle, the vacuum isn't very much, slow idle it's a bunch but the key point is that it's always there. And when you got a vacuum on one end of your valve guides and atmospheric pressure on the other, there's going to be some amount of flow between them. The only way to prevent that flow from carrying oil vapor from he valve gallery into the combustion chamber is to install a seal on the valve stem.

Volkswagen began using valve stem seals starting with, I think, the 1964 model year (i.e., engines produced after August of 1963). That's those little black donuts you find stuck to the screen when you do an oil change. That's right; those niffty ‘seals' get baked as hard as a bride's biscuits, break, and end up in the sump. Which is sorta sad because if you did have good seals on your valve stems you wouldn't use so much oil and you'd probably have no trouble passing your smog. (The engine in my 1965 bus measured 71ppm HC out of an allowed 670ppm. Yeah, I know - it's so old it's exempt. I have it checked now and then just to show off :-)

I've got good valve stem seals on all of my air cooled VW engines. You gotta do it yourself but I figure it's worth the effort, especially since I do a few others things as well.

Valve Guides

If you order valve guides for an air cooled VW from five different sources, you're liable to get five different sizes. If you've ordered STD the body of the valve guide should be about 12mm in diameter, have an overall length of 61mm and a bore just a tad over 8mm. But all of their other dimensions are liable to vary from one manufacturer to another. Fer instance, valve guides come in standard plus two over-sizes, the largest having an OD of 13.25mm. STD guides, with OD of about .4577, you can make out of half-inch diameter bar stock but second-oversize, some outfits use 14mm, some use 15mm, others use 9/16... you never know what you're going to get. Which is no sweat, since they'll still fit. What's different is the maximum OD of the rim around the top of the guide. And that becomes significant if you want to use valve stem seals, because the seal plugs on to the top the valve guide.

A good (i.e., modern) valve stem seal sockets down onto the guide with a fit so tight you have to drive them on and need a special pry-bar to get them off. (Actually, they never come off once they're driven on. When the guide becomes worn you throw the seal away when you remove the old guide.) The problem here is that since VW never used a good valve stem seal on its air cooled engines, there isn't any spec for the height & diameter of the rim on the upper end of the Type I valve guide. If the guide is made from 9/16 stock (not uncommon for the larger over-size), that's what you get for the top-end of the guide; ditto if it's made from half-inch stock.

Whatcha gotta do is measure the guides then find a valve stem seal that will fit that particular diameter. At least, that's the theory :-) What you'll probably end up doing is using VW Rabbit guides for your intake valves... and VW Rabbit valve stem seals. Which ain't a very good idea, even though lotsa folks do it that way. (They say it gives them better flow.) Rabbit guides are about an inch shorter than Type I guides. That leaves a lot of the valve stem exposed and that can cause the valve stem to collect crud and stick open. Not a major problem for a car engine although it's a pain in the ass since you have to pull the head to clean things up. About the worst thing that can happen is to use the shorter Rabbit guides for both intake & exhaust. Don't work. The Rabbit guides are shorter because the engine is water-cooled. Air-cooled, you need the longer Type I guide to provide the required heat-transfer surface. Use the shorter Rabbit guide, the exhaust valve eats it in a matter of miles. Classic shade-tree repair, though... guarantees you'll break down just far enough away so as to become someone else's problem :-)

I don't use Rabbit guides.

But I do use Rabbit seals. And Toyota seals, some of the time.

What I do is buy a batch of valve guides. If they're fat, which is usually the case with oversize guides, I machine the top of the guide to accept the Toyota valve stem seal, which needs an OD of at least .525 inches for a good fit. The Toyota seal is fairly long - about three tenths of an inch - so I may need to grind off some of the skirt.

Most STD valve guides are made from 13mm (.512) or half-inch stock, depending on what country they come from. You can fatten up a 13mm guide to accept a Toyota seal by knurling the upper lip of the guide but in most cases you'll get a better fit if you turn down the upper lip to about .425. That will allow it to accept the Rabbit seal.

How do you machine it? In a lathe. One of those little hobby-lathes will do. In fact, if you got kids around the shop modifying valve guides using a baby lathe is one way to introduce them to the arts of Tubal Cain.

The Cost of it All?

Durt cheep.

Figure about a buck each for the seals, one to three bucks for the guides. Shop around. A couple of years ago I bought a batch of 100 Type I valve guides from a VW engine rebuilder who was going out of business. Two bits each. J.C.Whitney occasionally offers VW engine parts on sale; I've bought guides from them for as little as a buck each.

Ordered via the Internet I think I paid eighty-eight cents for Rabbit seals and two thirty-five for Type I valve guides. For comparison, a local VW dealer wanted over seven dollars for the seal and nearly twenty bucks for a single valve guide. (Apparently no one at VOA has ever heard of Adam Smith. :-)

Are Valve Stem Seals Worth the Trouble?

That's up to you to decide. The lubrication mods provide a significant improvement to the Type I VW engine but increasing the amount of oil to the valve gallery guarantees a dramatic increase in oil consumption... unless you install valve stem seals.

I like dull engines; engines I don't have to worry about nor tinker with. But at the same time I want my engines to be as fuel-efficient as possible, more powerful than the other guys and to last five times as long. The lubrication modes address those issues but the mods are impractical for street use without effective valve stem seals. So for me, yeah, it's worth it. Your mileage may vary :-)

Can I Do It?

Of course you can! Real engine-builders have been doing it that way since the early sixties. Just because you haven't seen it the magazines doesn't mean you won't find it at the finish line. You'll have to find someone with a lathe to modify the new guides and you'll need some tools & a simple wooden fixture to hold the head while drilling out the old guides, but that's what mechanic's do. An you are the Mechanic-in-Charge.

-Bob Hoover
-Feb 2003