Propeller 01 The Blank & Other Preparations

A good propeller begins with a good blank. The one shown here is not especially good. It lacks sufficient squeeze-out at the glue line. But it's good enough to serve as a training aid.

The blank shown here is made of pine weighing about 32 pounds per cubic foot. Which is pretty heavy for pine. The blank is a full six feet long, four inches more than required. Reducing the blank to sixty-eight inches will of course reduce its weight, as will carving the blank to the usual propeller shape. As shown the blank weighs twenty-two and a half pounds.

I've taken the trouble to mention the weight -- and the fact it will weigh less as the work progresses -- because I can't lift it, thanks to the cancer (mentioned in earlier posts). And since I can't lift it you may see me doing some rather silly things with the blank. That doesn't mean you should do the same :-)

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The blank began as four pieces of shelving. To make-up the required three-inch thickness I had to stack the four pieces atop one another. Since this blank is specifically for training you may elect to use a different number of laminations, so long as you adhere to the basic rule: More laminations is better than fewer laminations.

In the same vein, I've used pine. You may elect to use a different specie of wood such as hemlock, cedar or what-have-you. But I think it would be wise to stick with softwoods, at least for this particular prop. 'Real' props are often carved from hardwoods but as you are about to see, a good deal of what you must learn has nothing to do with the type of wood you are using; in theory you could learn with a styrofoam blank.

I've used Weldwood 'Plastic Resin' glue on this practice blank and intend to use it on the real blank as well. 'Real' propellers generally use Resorcinol but it has become difficult to find. Some prop-makers are using epoxy and I've even heard of urethane being used, but the choice of adhesive is really up to you, since all commonly-available adhesives are stronger than the wood you'll be using.

In any case, given the amount of adhesive you'll be using, it's cost is insignificant compared to the cost of the airplane as a whole. Which is one of the reasons you want a good squeeze-out. A good, sloppy squeeze-out is the best insurance against a glue-starved lamination. If you'll examine the photos you will see that I did not get a good squeeze-out with this blank, which is why it would normally be rejected.

Valve Job - Replacing Guides

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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

How to Fix a Broken Back

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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

I Need Your Help, Please!

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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.

The trouble is, THEY DON'T PROVIDE ME WITH A RETURN ADDRESS!

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 veeduber@isp.com 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

Oh My Aching Back!

I've got a broken back!

As a result of the cancer, my third spinal vertebrae has suffered a compression fracture. This was discovered by last weeks MRI ( Magnetic Resonance Imaging ). The fracture explains the pain I've been experiencing, as well as the steady increase in that pain. A month ago I could work standing up for about 20 minutes before the pain became too much to take. That has been steadily decreasing until it's reached the point where it takes barely five minutes for the pain to rise to the point where I can't stand it and have to sit down. Sitting down causes the pain to stop increasing but the pain is still there and it takes a lot of pain-killers... or a lot of time... before I can move about.

Imagine not being able to take a pee... or to fill a glass of water at the sink... or even to walk from the bedroom to the kitchen.

So they did the MRI and there it was: the third lumbar vertebrae was so badly honey-combed by the tumor that it had been crushed: a compression fracture.

There is a surgical procedure that is supposed to offer some relief. How much depends on who you talk to. So far I've found only one person who has had the procedure done; a woman a little older than me who suffers from osteoporosis. She says the pain is less but has not been totally eliminated. To her the advantage is that the pain does not become steadily worse when she tries to do housework or ride in a car.

If you talk to the people selling it, the surgery is the best thing since beer in cans.

I guess I'll just have to wait and see. Personally, I don't see how the pain could be much worse. It has gotten to the point where I'm pretty much trapped; unable to move about. If I can't move, I can't get the exercise I need to keep my remaining muscles in shape. If I just sit here like a bump on a log my body will slowly deteriorate to the point where I can't move, not because of the pain but because I simply lack the ability to do so.

The surgery is an out-patient procedure that takes only a few hours. The earliest they can get me in is about two weeks from now; maybe a little less. I'll try to keep you posted.

-R.S.Hoover
-24 October 2008

MRI, Clearancing the Camshaft and Me

The x-ray mentioned in my last blog entry revealed nothing amiss. The pain is still there as is a monstrous swelling the size of a grapefruit that is its apparent source. But the swelling is all soft tissue; it offered nothing for the x-rays to 'see.' So I pulled up my pants and went home, accompanied by my lump and the pain. The next step was to schedule me for an MRI scan, which underwent on Friday.

MRI stands for Magnetic Resonance Imaging and takes advantage of two fundamental laws of physics. The first is the fact that every atom has a unique resonant frequency. The second is that fact that if you disrupt the local magnetic field, each atom will generate a small but distinct signal. The MRI machine provides a powerful magnet to disrupt the local magnetic field and a sensitive receiver to pick-up the signal given off by those disturbed atoms. (Yeah, I know... but I'm not talking to you, I'm talking to folks who don't have EE after their names.) That signal is fed to a computer and the computer puts the signals together to form an image. Of course, that image is only for a single slice of the target. To come up with a picture that makes sense you'll have to run the thing down the length of whatever you are trying to make an image of, then have the computer put all those 'slices' together.

The big advantage of MRI over basic x-rays is that everything generates a 'signal' of some sort. The signal from good tissue will be slightly different than the signal from bad tissue. That means you can now 'see' soft tissue, whereas the x-ray would blast right through them and not 'see' a thing.

I'm a ham radio operator (KA6HZF) and have a strong interest in stuff like MRI machines, which were invented only a few years ago, relatively speaking (they're about three years older than the Personal Computer, for example). Imagine a sewer pipe about as large as your shoulders. Rig a pair of runners on each side of the interior of the sewer pipe. The runners support a narrow table, allowing it to be rolled into the sewer pipe. You lay upon the table and get shoved into the sewer pipe, your shoulders touching the sides, your nose scant inches from the plastic surface. If you are even moderately claustrophobic, this is not the place to be.

An enormous coil is built around the sewer pipe and an equally enormous magnet spins around the outside of the sewer pipe. The magnet will cause anything within its field to give off a faint but distinct signal which will be picked up by the coil and fed to a computer. The computer performs a bit of mathematical magic on the signal and aligns that slice with the previous slice so that when you are done the slices will form a coherent image. The nice thing here is that the image will show soft tissue as well as bones and the odd bits of shrapnel.

This past Friday I reported to the Keeper of the Keys and she sent back to where Bill, ex-Air Force but a pretty good guy in spite of it, laid me down on a narrow bed and shoved me into the sewer pipe. Hit the big red button and the MRI machine commenced to hum and groan... okay, the groans were mine but the machine did hum a bit.

It took less than an hour for the MRI machine to slice me into electronic ribbons which were recorded by the local computer and stored. These would be processed by a more powerful computer which would combine them into an image. The image would be sent to the physicians and they would try to figure out what was causing the bulge on my hip.

So whats all this got to do with camshafts, fer crysakes!

Well... nothing, really. Except the camshaft in the picture is going to be installed in an engine fitted with a crankshaft having a throw of 41mm (stock is only 34.5mm). That means the connecting rods are sticking out 6.5mm farther than on a stock engine. And that means they are going to hit the camshaft.

Six and a half millimeters is 0.2559" - a full quarter of an inch. In the stock engine the connecting rods miss hitting the camshaft by about an eighth of an inch. In the big-bore stroker the connecting rods are about an eighth of an inch too long. So we have to grind away about an eighth of an inch to give them clearance. In fact, that's what this operation is called: Clearancing. It applies to the crankcase as well as the cam shaft.

The tricky bit is knowing where to grind away, and how much to grind away. In the case of the cam shaft, if you'll click on the image it will give you a blown-up view, allowing you to see where I've ground away metal from cam shaft. You can also get some idea of how much metal I've removed. If this is the first time you've clearanced an engine, odds are you'll go a bit too far. What you need is a gauge, something to tell you when you've gone far enough. (Remember, the camshaft must be strong enough to withstand the torque needed to open the valves. If you grind away too much metal... or leave a sharp edge that will allow a crack to get started, the camshaft will break.) Fortunately, you already have a gauge. It is the assembled crankshaft. That is, the crankshaft with all four rods installed. With the camshaft properly meshed with the crank (ie, with the dots properly aligned), rotate the crankshaft and observe the position of the rods as they swing past the camshaft. You want about sixty thou of clearance. Any more and you'll just weaken the camshaft whereas any less and you're liable to have a collision when the engine heats up.

-Bob Hoover

California Living

Mondays are always interesting. That's when we get to do all the things we should have done on Friday but forgot, and over the weekend when we were just too damn lazy, such as the Worm Roundup.

I'm a native Californian. I've never seen anything unusual in being able to pick vine-ripe tomatoes for the Christmas dinner salad. Or going skiing in the morning and surfing in the afternoon. Or visa-versa, depending on the tides and the weather.

But if you fail in your duties as a Worm Rounder-Upper there won't be any ripe tomatoes for your Christmas dinner, nor those BLT's you like to build. But Monday is also the day when the physicians treating my cancer decreed that I would have Mr. Roentgen's Mysterious Rays blasted through my right hip, into a photographic plate about 12 x 18. In fact, X-rays are about the last ditch when it comes to photographic plates, what with regular cameras and film being replaced by memory chips, disks and tapes. (I've got a hunch we'll soon see the last of film in x-rays, as a layer of fluorescing material is bonded to an ultra-high density array of photo-sensitive sensors. The resulting image would probably be a couple of gigabytes at a minimum and a terabyte isn't beyond reason. The advantages of a digitalized x-ray are almost too numerous to mention. This method is already in use in various scanning devices,(*) in which the digitalized data from a MOVING x-ray -- or other short wave-length emitter -- are fed into a computer which then generates a 3D image of the target area. (*) CAT Scan, PET Scan, SAT Scan and so forth.) But so far, no one has applied that technology to the Plain Vanilla x-ray machine, where you pump a few million volts between the cathode and the anode of a specially configured vacuum tube and direct the resulting X-rays toward the target, behind which you've placed a sheet of photographic film. To get to the film the x-rays gotta pass THROUGH the target, be it toes or telephones and the resulting image depicts the ease or difficulty of that passage.

The cancer is in my lower back and the pelvic girdal. Recent episodes of pain indicate that it may have gotten to my right hip as well, hence the need for Mr. Roentgen and his Rays. Which kept me from my duly appointed rounds in the garden and allow certain visitors to reach an unruly size, as shown in the photo. We don't use insecticides. But a lot of folks do. The catapillars quickly become immune to the stuff. But the birds that would normally eat the catapillars don't. The insecticides build up in the catapillars until they become toxic to birds. No more birds.

So I pick them off. Doesn't take long because we only have about half a dozen tomato plants, more than enough for our needs. A lot of folks from exotic places like Detroit or Buffalo give you funny looks when you mention growing tomatoes all the year 'round. But the worms believe it -- big wormy smile on their little wormy faces. Mebbe I could rig up some kinda portable X-ray emitter, couple of passes and all them caterpillars would be gonners. But until then I am the Official Worm Rounder-Upper. One of the burdens of living in California.

-R.S.Hoover