View original topic: Less is more 1/2 VW
rebelce Sat May 06, 2017 5:51 am

I know you folks suffer your fair share of kooks but honestly, I'm not one of them. 1/2 VW are a well known and respected way of getting ultralights into the air but in the search for a little more power they've gone up to the 84X94 max and are starting to break cranks with the chevy journals. I wanted to get a little more and I really dislike having the exhaust sticking out the front towards the prop. So here's my idea and I would sincerely appreciate your input. It doesn't appear to be much of a difference between the stock case cylinder bore of a type 4 and a 94mm overbore on a type 1. If that's true, why not use a 96mm Biral T-4 cylinder and a cut in half T-4 head. The hard part would be spreading the studs out. The T-4 has much better breathing, TWO bolt holding down the rocker arms and the exhaust points straight down. If the cylinder needs to be spaced up, I could machine a spacer, use the 4 original stud points to hold it down and redrill for new studs. I don't know if that would work as I don't have access to the dimensions of a T-4 or T-1, stud spacing or case bore. What do you think? Can this be done? Remember, it's an opposed twin, no bore spacing to worry about. Day 1) Well, I started machining the cases today. There are two ways to build one, full case and cut case. Cut case is 5# lighter and that's what I did. Instead of a straight cut I put a jog in it to save the pickup screen and cover plate. Just has always looked goofy to me to cut a divot off one edge and leave the screen off. This way you also get the added benefit of a set of case stiffeners in the corners of the bottom to match the tops.

Bashr52 Mon May 08, 2017 5:04 am

What do you do to seal up the cut case and make sure the oil passages and stuff all work out? Weld plates on the cut side?

rebelce Mon May 08, 2017 7:55 am

A 3/16th aluminum flat plat is generally just bolted to the back. The bolt size varies, everywhere from 10/32 and 1/20's all the way to 3/8th in the corners for the engine mounts. I need to download some pictures, it would help. This has been done for years and as Micky Mouse as it sounds, works well. For the oil passages, other than blocking the main and lifters, it's left as is. I'm not going to do that. I'll install an oil filter where the cooler used to be and permanently route the oil through it. From there it will go around the intake manifold then to the main galley. Once upon a time, Mosler made 1/2 cases just for this and used Scat split heads, hard to find now.

rebelce Mon May 08, 2017 5:25 pm

Picked up some more parts today. A set of type 4 heads, have no idea of what they are, "all cleaned up and naked" good for measurements and hopefully a starting point. A 21mm flat cam oil pump. Also a half T-4 carb manifold, a Harley CV manifold to go with the Harley CV carb I have and a used crankshaft from GY6 50cc scooter. Just a couple substitutions for the normal "Eye of newt and toe of frog" most people use on these builds. If I had the guts to do it or could find someone will to help, I'd go for an 84mm stroke. Bigger is better, any time you can get away with it. I feel this is totally doable, though it would be nice to have the reassurance of some real numbers.

rebelce Sat May 20, 2017 7:55 am

The T-4 heads came the other day. Can't say they were pristine but for my purposes they are fine. I believe they're early 2L, 022 101 372G. First order of the day was to carefully cut one in half. It would seem easy but the valve train and the cylinders are slightly offset and require two cuts with a small intersecting cut, to join them. Getting the heads also answered the question as to stud spacing. Three are just barely overlapping while the lower outside stud is fully outside the old stud. Cool but also directly in the return oil channel cast into the case. Still doable, just need to incorporate a return line into the case. Now to figure out the best way to install dual spark plugs. Two on top or on opposite sides of the chamber. Need to find the best cam too, so many questions.

rebelce Sun Jul 02, 2017 5:32 am

Well, I've spent almost all of June riding a backhoe in the backwoods of Arkansas trying to get a pad ready for a future shop. On to the fun stuff. Picked up a set of swivel foot adjusters as well as all the 1.75 inch aluminum tubing for the intake manifold. Stock Harley CV carb and intake. I'll machine up some stubs for the heads and use clamps to hold the pieces together. Also snagged an old school capacitor for the DC side of the ignition. Need to save the weight of a battery and hand proping it will be fun. 84X96 turns out to be 1200cc's, seems right!

SBD Mon Sep 04, 2017 7:04 pm


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