Conversion - 1/2 Carr

Rev - Nov 29, 2017

By David E. Carr (EAA 78609)
Sport Aviation - January 1975


EVER SINCE THIS flying game started, amateur builders have been confronted with the problems of a powerplant. Light engines have always been scarce and high priced. Right today there is a very limited choice for the man who isn't free from the worry of expense." This is a quote from the 1933 Flying Manual. These words are as true today as they were in 1933. Today there is a need for a reliable, inexpensive, ultra-light four stroke powerplant, just as there was then. From my home on the northwest side of Portland, Oregon I can just about see to Cornelius, Oregon where Les Long wrote the foregoing quote 41 years ago.

If you have read the 1933 Flying Manual, you are aware that Les Long designed several ultra-light aircraft in the era. In doing so, he generated a need for an ultra-light engine for himself and decided to build one from cheaply obtainable common parts, which resulted in the Long Harlequin Motor.

Last winter, while finishing up my Pietenpol Aircamper and before the first test flight had even been flown, I had dreams of building a lighter, single place aircraft in an ultra-light category. Designs such as the Longster, Heath Parasol or a Pixie interested me. With these designs in mind, I started thinking of what I could do for an engine.

I had been kicking around, in my mind for sometime, the feasibility of cutting a VW engine in half. Not wanting to cut into a good 4 cylinder engine, I made a trip down to my local VW repair shop. After explaining my intentions to the owner, he said he had several engines that had been damaged internally on the fly wheel end, and for a promise that I would show him the twin when it was finished, I was given those engines.

Following is a brief explanation of what I did to achieve a reliable running twin engine.

After thoroughly disassembling, cleaning, and inspecting one of the engines, I started sawing the engine in half, using a band saw. First of all the crankcase is cut in half aft of the center main and a plate is welded on the back of the cut off portion. The camshaft is cut off aft of the center main and the same for the crankshaft. Counterweights are welded on to the crankshaft so that it is perfectly balanced. The heavy duty thrust bearing which was on the flywheel end is put on the propeller end of the crankshaft to absorb thrust loads. A magneto coupler is fastened to the rear end of the camshaft and a magneto and spacer are mounted directly to the rear of the crankcase.

Since the VW cylinder head is symmetrical, when cut in half one half becomes the right cylinder and the other half becomes the left cylinder. The intake tubes and a plate to seal off the rocker box are welded onto the back of the heads. The intake manifolds are simple sink drain fittings. The carburetor mount flange is cut off of the existing VW manifold. The carburetor is from a 36 hp VW engine, bought very cheaply at any wrecking yard.

The propeller hub is built by using the existing fan belt pulley; the pulley is removed from the hub and a simple 6 bolt flange is welded on. The engine mounts are attached to the top and bottom of the crankcase with the flange bolts and a simple U-shaped bracket.

The engine was then mounted on a test stand fabricated from angle iron and the day finally arrived that I had been waiting for. Now to hear my 80 lb. twin run. The accelerator pump was left in the carburetor, so the starting procedure is thus: mag switch off, 2 squirts on the accelerator pump, stand behind propeller, pull through twice, mag switch on and pull once and the engine starts so easily it seems like it has just been waiting for this. The engine idles very smoothly and runs smoothly through the entire RPM range!

From the very beginning of the project, I hoped to build an engine that would be as simple as possible to build with the least amount of sophisticated tools and with parts that are economically purchased anywhere. The most difficult part of the entire engine is welding the magnesium plates to the back of the crankcase, and this is a simple job if you have access to a Heliarc welder. For those who do not have a Heliarc welder or cannot have it done locally, I will be supplying this service.

The distributor can be left in the engine making an alternative to using the magneto ignition system. The basic engine can be easily constructed, complete and ready to run for less than $100.00. A magneto version can be built for less than $200.00. With an investment of approximately 100 hours of your time, you have your engine built.

Depending on which size engine you choose to convert, I would estimate HP ratings to be half plus some due to better carburetion. I am now in the construction stages of building a 900cc version with which I hope to achieve a horsepower rating of 35 to 40.

Complete and professionally drawn plans are being made and a material kit, castings, machined parts and a magneto will be available.

I would like to take this opportunity to sincerely thank Blair Krakowski for his enthusiastic help in this project, also Art Matson for his beautiful drawings and Mike Stewart for the beautiful photography work. Without the help of these talented men, this project would have been a monumental task.

Those wishing further information can obtain this by ordering an information package for $2.00. Mail to the following address: Carr Conversion, P. O. Box 671, Beaverton, Oregon 97005.