I'm sure a number of the members of this board have seen some of my engines and videos but for those who haven't I'm posting this one. It's my model of the Holt tractor engine. I had seen several of them built over the years and spoke with the builders to get their feelings about the castings and such. From what I heard I wasn't to keen on buying the castings, not because of the quality but rather the way the engine had to be machined. I sent for the drawings to see what was required to build it and found a rather crude way of finishing the interior surfaces of the block to accept the main bearings. At that point I decided to scratch build my engine. I redesigned the crankcase to be split along the main bearing line, the casting is a one piece affair. After machining the crankcase I just moved on from that point and scratch built all the other parts except for the manifolds, too many bends, and the large flywheel, too big to chop out of a hunk of iron. For those I ordered the castings. I scratch built the carburetor to the drawings but when it came time to start the engine I had all kinds of problems. I tinkered and swore, redesigned and machined, tinkered and swore some more and finally opted for a simple model airplane type air bleed carb. With that I got the engine running quite well and this allowed me to fine tune the ignition timing. I have since tried other carb designs but have settled on the air bleed carb. Since the video was shot I have machined the excess stock off of the carb to make it look more realistic and I have hooked up the governor linkage. Here's a little information on the engine: 1.00 bore x 1.25 stroke, spark ignition, splash oil system, my own designed water pump, fan and shroud. It's machined mainly from 6061 aluminum with iron sleeves pressed into the aluminum jacketed cylinders. The crank is steel and the rods are bronze. The main bearing inserts are bronze. Each piston has two compression rings. The radiator was made from the Jerry Howell design and I stepped off the word Holt on the face of the top tank. It starts and runs as well as any engine I have built. So without further adieu here's the video clip.
George D. Britnell
