For several years, I toyed with the idea of building an engine out of an air compressor. Each time I saw an article in Gas Engine Magazine about another homemade creation, the interest was rekindled, only to fade each time for a lack of resources - especially because I didn't own an air compressor.
After I completed a Briggs & Stratton Model FH restoration for a friend (January 2004 GEM), I set my sights on an overhead-valve Briggs. Since retirement income precluded the purchase of such an engine, I decided to make my own and call it a Briggs & Stratton Model 'KH.'
I started with the crankcase from a 3 HP horizontal-shaft Briggs & Stratton Model 82000, but it was missing several components including valves and a connecting rod. I appropriated these parts, as well as the crankshaft, flywheel and ignition coil, from a 3 HP Briggs & Stratton vertical-shaft lawn-mower engine of older vintage.
When I told local old-iron enthusiast Don Spero what I was planning to build, he said he had something that just might be useful for this project. The next day, he presented me with a sealed box. When I opened it, I found a brand new aluminum head, complete with installed valves and attached rocker arms! A quick check revealed the head was made for a cylinder with the same 2.375-inch bore as the block I was using to make the Model 'KH.'
Getting to Work
One problem became immediately apparent, however. My original plan was to use an atmospheric-intake valve and bring the exhaust-valve pushrod up through the original valve guide. That plan was impossible with the new head assembly since its valves are mounted at an angle, and the rocker arms protrude beyond the side of the head.
About this time, John Heath's article about his Curtis Crudo homemade engine appeared in the September 2003 GEM. Taking some inspiration from John's Crudo design, I decided to move the tinning gears and camshaft outside the crankcase as he had done.
I fabricated adapter plates to mount the head assembly, carburetor, muffler and the U-shaped mount for the timing gears from 3/8-inch-thick aluminum. I brazed a shaft bushing to the small timing gear so it could be secured to the crankshaft. I made the flywheel from a 10-pound barbell weight, which I trued on the lathe and bolted to a lawnmower blade holder. For a gas tank, I used a 5-inch length of heavy-wall copper tubing. I made the end caps from the bottoms of 15-ounce vegetable tin cans that I soldered in place.
I had planned to use an old Clinton carburetor from my junk box for this project, but it posed a special problem since someone had turned the idle-adjust screw in so tightly it had jammed and broken off. I drilled out the needle passage, tapping it to a 1/4-28 thread, and made up a new insert complete with an air passage, idle-bleed jet hole and a new 8-32 thread idle mixture screw.
The cast iron flywheel and the ignition coil I salvaged from the lawnmower engine were designed to use breaker points and a condenser. The crankcase I used featured breakerless ignition, so it had no provision for mounting and operating breaker points. Initial attempts at operating a micro-switch from the exhaust-valve camshaft produced a marginally adequate spark. Rummaging through my junk box, however, I found an original Briggs & Stratton conversion kit designed to replace the points and condenser on early B&S engines. I had purchased this unit many years ago but never used it. After installing it, the spark was extremely hot, and ignition timing was automatically established.
The governor also caused me some head-scratching because the air vane was located on one side of the engine, and the carburetor was located on the opposite side. My final design uses coat-hanger wire and two 90-degree pivot points with the final link to the throttle shaft passing through the center of the hollow rockerarm shaft. Finally, I added an air cleaner housing made from a tuna fish can.
Upon completion, the engine started on the very first pull and ran very smoothly after minor mixture adjustments. This project gave me a lot of satisfaction because it forced me to face each challenge and devise a solution that resulted in a nice-running engine. It is definitely one of a kind.
Contact engine enthusiast Ken Hollenbeck at: 607 Cherrywood Lane, Sister Bay, Wl 54234; (920) 854-2461.