# Steps to scratch build a VW

Discussion in 'Hangar Flying' started by Little Scrapper, Aug 13, 2019.

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1. Sep 3, 2019

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Properly venting the crankcase is important and easy to mess up. On my former Sonex the vent tube was a 1/2" diameter tube the ran over the top of the engine and down to the bottom of the cowl. I didn't like that it was dumping oil all over the bottom of the plane so I extended it with a smaller tube down to the bottom of one gear leg. Next flight my engine blew a ton of oil out the prop hub and all over the engine and cowl....what a mess.

I eventually made an oil separator that worked well to condense the oil vapor without creating back pressure in the crankcase.

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2. Sep 3, 2019

### blane.c

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Well that is simple enough. It does seem weird to me to have the shims external however.

If you pull the crank one direction with shims or you pull it the opposite direction with shims there is a change as to where the big ends of the rods will sit on the crank for each extreme? Or do the small ends of the rods float on the pin instead? I don't know maybe it doesn't matter but … .

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3. Sep 3, 2019

### Pops

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Rod side to crank clearance (Axial) is .004 to .016. I like .006. Notice it's about the same as the end play clearance. So as the end play wears in a high mileage engine and gets larger the small end of the rod will be floating on the piston pin a few thousands.
I also try to set the end play at .005/.006 .
I have had high mileage VW's that I drove to work where you could move the lower belt pulley on the engine back and forward and hear a clunk and moving close to 1/8". Will also have a rear main seal leak with the engine marking its territory. That is the time to have another new rebuilt engine on the engine stand for a replacement. Usually about 150K to 200K miles. Just takes a few minutes.
First time I helped to take a VW engine out was in 1965. Helped a friend replace the clutch, pressure plate and throw-out bearing in his 1963 VW Bug. First for both of us and we had the job done and engine running in 20 minutes.

Last edited: Sep 3, 2019
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4. Sep 4, 2019

### dmar836

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So thinking about it, isn’t the pressure plate on a car pulling in the “tractor” direction toward the back of the car? This would appear to be the same loading of a prop pulling forward. I realize the cam has end loads we deal with but could anyone expound on the direction of the end loads on the crank?
Dave

5. Sep 4, 2019

### akwrencher

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End loads from clutch are when you step on the clutch pedal, the crank reacts the load equal to the spring pressure towards the engine, not away from it.

6. Sep 4, 2019

### dmar836

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So when a prop is added to the pulley end the end play shims take the thrust and when a prop is added to the trans side the shims again take the load as they are placed on the inside of the #1 bearing?

7. Sep 4, 2019

### blane.c

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When the shims are on the outside of the case, between case and flywheel … do you assume a small amount of leakage for lubrication or ?

8. Sep 4, 2019

### dmar836

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There is a seal inboard of the shims.

9. Sep 4, 2019

### blane.c

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Maybe it leaks a little?

10. Sep 4, 2019

### blane.c

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If making a tractor engine with the propeller on the flywheel end the shims would be on the inside between the case and the crank throw? Apparently between the #1 bearing and the crank throw? And then to get the cam gear to line up correctly with the crank gear appropriate machining must take place? And then the cam shaft shimmed to stay in position? And then mumbly peg with various diameter cam gears to find the perfect one? Ah! What a simple engine. Can you measure the center of the crank to the center of the cam and know which cam gear you need? Or at least get it down to the fewest possible try's?

11. Sep 4, 2019

### dmar836

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I’m really not sure. I’ve not heard of anyone doing that or reading a spec. The Ford Model A is done like that. In fact, the cam bore is what one indexes from to line bore the mains.

12. Sep 4, 2019

### blane.c

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13. Sep 5, 2019

### 103

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Three shims are placed between the flywheel and the case. I did this just last week setting endplay to 0.0055 ".

After confirming the shim stack you install a silicone rear seal. Install the flywheel again for the final time Torqued to 217+12-0 ft lbs and confirm end play again. If all is good install the mag drive dog and dynamo magnets ring. Proceed to install accessory case/plate next step timing the mag....tune in later

I do want a definitive shim location for a flywheel drive engine.

The end play is set without An Oil film once the engine is running the shims will get lubricated. This is part of the shim function to created a slip plane. One shim against the case and flywheel one sandwiched in between slipping past each other with a slick of low pressure oil contained by the big red rear seal from the motherland Germany.

Last edited: Sep 5, 2019
14. Sep 5, 2019

### karmarepair

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yes, in the sources I have available to me.
yes, in the sources I have available to me.
Nope, see below.
Nope, see below
THIS. Mind you, this is an elaboration that most VW rebuilders don't seem to bother with. Back in the Day, you could get I think 9 sizes of cam gears. Now, most aftermarket gears are unmarked.

According to my sources, not to the degree of precision needed, at least not with the tools available to the average mechanic. Bob describes doing it here https://bobhooversblog.blogspot.com/2007/01/dialing-in-your-cam.html and suggests using 3 "gauge cams", stock cams with the gears still riveted on them.
"Immediately after checking the fit of the main bearings to the crankshaft and case, the driver gear is installed on the crank and the crankcase is gauged to discover what size cam gear is needed. One of the most practical ways to do this to is to obtain three stock cams for use as gauges. With a +2, a 0 and a -2, it takes only a few minutes to figure out the right size cam gear for any crankcase. All you have to do is install your gauge-cams in your crankcase and check their lash against your crank."
Read the rest of his post (a little long-winded, as he was) for the details. "Gauge Cams" you can get on The Samba. This link will not last very long, but this guy has cams with gears attached for $2 each. http://www.thesamba.com/vw/classifieds/detail.php?id=2227540 This guy wants$4 apiece. I think for this purpose is matters not if you have a "flat", "Dished", "36 HP" or "1600cc" cam, as long as it's NOT a Type IV. I'm NOT proposing you use such a cam to assemble your engine; it's just a gauge to find the right GEAR size. If one of your "Gauge Cams" has the right size gear, then drill out it's rivets, spot face it, and bolt it to your NEW stock or mild street grind cam. This is the cam I bought for my engine http://schneidercams.com/248-54Fvolkstype1.aspx

Last edited: Sep 5, 2019
15. Sep 5, 2019

### GeorgeG

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Uh, guys -- I had a VW shop for 15 years, rebuilt a bunch of air-cooled engines. Other than exhaust valves, the only other part I would NIVVER re-use was the cam and lifters. They are a high-wear item, they're not all that expensive, and new cam and lifters is the only way to go. And you'll prob'ly want a special-grind cam, anyhow, to get your power curve where you want it.

16. Sep 5, 2019

### 103

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The Schnider 248-54C is one I would consider when building an Hoover decribed it as a "Chugger Cam" with modestly more low end torque than a van Cam. I recently stumbled into the CAM with claims that seem too good to be true. Waiting on the polish factory for a.quote. they claim to shift the torque curve down 4-500 rpm. Check out the 3 boxer engine links within for curves.

http://vaxell.com/?page_id=1043

Claims are.this cam would convert my.2276 into a mythical 100hp engine. I would be more interested in swinging a larger prop at lower speed and producing 65hp for take off at 2750rpm.

I am a skeptic a singular cam can do this much.

17. Sep 5, 2019

### Pops

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Lets face it, we are not a very large market for a cam for torque at a low rpm. Put me in the skeptic box.

In building VW engines as a side business for many years, I had one engine where the cam gear was to tight. Having lots of parts to check, I found a cam gear that fit. I think Bob Hoover said that about 95% would be a Zero. So your chances of having a cam gear to small or large is very small.
BTW -- When building a aero-VW engine, you will have to put the TDC and the BTDC timing marks on the prop hub. Go to Bob Hoover instructions on how to do this.

18. Sep 5, 2019

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Interesting, I had forgotten about them. I would be curious to see what they quote you for a cam, so let us know what you find out.

I agree that the cam alone is not going to bump up your 2276 to a 100 HP monster. Engine tuning needs to address the mass air flow through the entire system: from intake, through the engine, and out the exhaust. Cam selection is one aspect of that middle part of the equation.

The volumetric efficiency of "typical" VW installations, as reflected in the performance claims of Great Plains and Hummel, are pretty low: down around 70%. There is plenty of room for improvement with attention to tuning.

Vaxell's VX 1001, the same displacement as your 2276, looks like it is getting 90 Hp at 3200 RPM. If we assume a BSFC of .46, that works out to a volumetric efficiency of 88%. That's on the higher end, but achievable.

19. Sep 5, 2019

### dmar836

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Hearing these numbers, I kinda wonder what guys are building VW conversions for. Meaning, what aircraft are they putting them in? From what I’ve seen most aircraft with VW engines were designed specifically for the VW engine and therefore were not expected to have more than about 60 hp.
I’m all for higher performance (in other’s applications) but the VW is traditionally used for a fairly specific application just like a smaller two-stroke. The engine weight is fairly high for the HP it can put out.

20. Sep 5, 2019

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