Saturday, November 29, 2008

Valve Job - Replacing Guides

The cast aluminum heads on a Volkswagen engine are fitted with four valve guides made of phosphor-bronze. The stems of your valves are installed in the guides. As the valves open and close, the small amount of clearance between the valve stem and the valve guide provides a direct path to the atmosphere. This isn't an especially good idea, so the valve guide is usually fitted with a seal. In the HVX mods I discuss the seal and show how to install them.

As the valves open and close they cause the valve guides to wear. The more they wear, the bigger the gap to the atmosphere and the more the valve will fail to run true. Due to the high temperatures present around the exhaust valve, the problem of a worn valve guide is more evident with your exhaust valves.

We periodically check the valve guides for wear. When the wear approaches the allowable limit, we replace the valve guide(s). The guides for the exhaust valves typically wears about three times faster than the guides for the intake valves. That means we will replace the exhaust valves about three times before we have to replace the guides for the intake valves. The exception to this rule is when you use the shorter valve guides from a water-cooled VW engine for your intake valves. (This modification is done to improve the in-flow at high rpm and does not apply to flying Volkswagen engines.)

To replace the valve guides we use a core drill, a suitable punch or drift, and simply drive them out. To install the new guides we heat the heads to 450 degrees on the Fahrenheit scale, chill the guides in dry ice or propane, and simply drive the new guide into the head. The first picture shows the step-drill and piloted driver used to replace (and install) VW valve guides. The picture on the right shows the stepped core-drill used to drill-out the valve guide before it is driven out of the head. When the valve guide is opened up in this manner it loses most of its grip on the head and can be easily driven out with a suitable punch or drift. The core drill is home-made. It starts out as a 7/16" drill bit. A half-inch (0.500") of the tip is ground down to a diameter of 0.3125"

The picture on the right shows the stepped drift used to drive the valve guide out of the head after it has been opened up by the core drill. The tip of the drift is turned to 0.308" for a distance of 1.125". The shank of the drift is 0.450" for a distance of 3.0". The drift started out as a standard 6" pneumatic drift but any bar of 1/2" steel can be made to serve.

-Robert S. Hoover
-30 Nov 2008

Saturday, November 8, 2008

How to Fix a Broken Back

Sorry, no pictures.

When Multiple Myeloma attacks the bones of your skeleton it does so one cell at a time. The resulting structure closely resembles a honeycomb, for want of a better comparison. When enough of the bone cells have been attacked the bone will no longer be able to bear its accustomed load.

When that happens, the bone BREAKS.

A sneeze can shatter your ribs. Bending down to tie your shoe can break your arm.

LIFTING A VW ENGINE can shatter your spine.

A Volkswagen engine weighs about 185 lbs. I am accustomed to picking them up and moving them around the shop with no problem. After I was diagnosed with MM I couldn't even pick ME up... and couldn't walk around my shop... unless I was braced with two canes.

I had crushed the third lumbar vertebrae in my spine. (Where's that? Put on a pair of skivvies, the waist band will fall right across the 3rd lumbar vertebrae.)

Being thicker, the top & bottom of the vertebrae was okay but the column between them was honeycombed and my normal activities -- probably lifting something -- crushed the vertebrae. Oddly enough, except for the initial fracture, this was not especially painful since it did not involve the spinal cord. So long as I assumed a posture that had me leaning forward, I was free of pain... until I had to bend or turn, in which case the pain could be so bad that there's simply no way to describe it. In time, this forward-leaning posture would have become my NORMAL posture, and the resultant pain would make my life a living hell.

To correct this abnormal posture I had to lay on my stomach and allow my spine to be stretched out to its original, pre-fracture dimension. This was quite painful but the pain was overcome with drugs.

The table on which I laid slide back & forth on a rail. There was an X-ray machine situated above the table and a fluorescent screen below the table, allowing the radiologist to 'see' my spine. The area above the fracture had been numbed with local anesthetics and I had been given additional pain-killers and tranquilizers.

The radiologist then inserted a large diameter needle (ie, 11mm or about 7/16") into the vertebra's crushed space, into which he pumped a fast-curing glue that served to straighten my spine and return it to is original dimension, or nearly so.

I was sent home after the procedure, higher than a kite from the pain-killers but literally feeling no pain. That was on Thursday the 30th of October. Today is the 8th of November and I'm feeling quite well.

The procedure is called 'vetebroplasty.' The procedure was developed in France in 1984 and is familiar to a number of Navy subscribers on this Newsgroup who have been using it to repair odds & ends of uncle Sam's sea-going machinery since the late 1970's, substituting JB WELD and a grease gun, instead of the more expensive medical equipment.

So... howz it working? It's a bit too soon to say for sure, but it seems to be a success, although I have to be careful whenever my wife is around, letting out a suitable moan or sigh and putting a hand to my back whenever she draws near. 'Cause if she thinks I'm getting better, she's got a list of 'honey-do's' as long as my arm... Ooops! Here she comes. I'll have to slip into Moaning Mode.

-Robert S. Hoover

Monday, November 3, 2008

I Need Your Help, Please!

Dear Friends... and you other folks too...

I get a lot of mail asking for help, mostly about engines but often about really important stuff, like how to file for immigration, or how to lay their hands on a copy of a local newspaper.


In most cases I'm both willing and able to provide the information they've asked for but I CAN'T.... because they haven't given me a return address. OR... they've posted their request to some blog entry I made years before and I've no way of telling which one they are talking about.

My e-mail address is Send your request to that address and I will receive it. But be sure to include your own e-mail address.

Alexander in Russia is still waiting to hear from me... because I don't know his e-mail address. Alexander isn't alone. I've posted aboout 300 entries to my blog and a lot of them have generated feed-back. But without a return address I can't answer them.

So please help me out, if you can.

-Bob Hoover