3 HP Homemade Hit-and-Miss Gas Engine

Homemade stunner
By Steve McClellan
December/January 2010
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Steve McClellan's homemade 3 HP hit-and-miss gas engine.
Photo by Steve McClellan
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A few years ago I decided to get a hit-and-miss engine. Not being able to decide what to buy, I turned to my machinery and piles of bar stock for the answer. I didn’t want a small model but rather a 3 HP-sized machine. After a few pages of sketches I set out to make some chips fly and built a homemade 3 HP hit-and-miss gas engine.

Quite a project
The base is often mistaken as salvage from an old engine, but it is all welded and ground flat stock. An 8-inch 6061 aluminum round was finned and bored to accept a new cylinder liner from a John Deere 4020, and a modified 4-1/4-inch piston was fitted. The head is a 2-piece design to allow for tuning compression, and has an O-ring seal. The valve modules are 4140 steel, and contain 318 Mopar valves in bronze guides.

It runs like a Deere
I machined a compact governor assembly and cam, and fitted them to a John Deere tractor timing gear set. The crankshaft is a 7-piece counterweighted unit with a 6-inch stroke and hard-chromed shafts.

I made a 6061 aluminum connecting rod with bronze bearings, and finished off the left side with a roller cam follower and dovetail slider assembly made from a Hardinge toolroom lathe cross-slide.
 
Waterloo to the rescue
My original drawings included machining round spoke 20-inch flywheels, but nearing the end of the project I decided on some Waterloo Chore Boy 18-inch flywheels found on eBay.
The engine runs on a homemade buzz coil, and sports a brass tag that reads “McClellan Gasoline Engine, Tama, Iowa U.S.A., 3 HP, Serial No. 0001.”

Slowing it down
 It started life on gasoline with 6-to-1 compression and was quite a beast. But after a few years of watching Stan Ellerbeck’s wonderful engines run on the bottle, I lowered my compression, modified the intake and machined a demand valve to run on propane. The engine is now much more pleasant to sit next to at the shows! I’m working on plans for a small Hvid now.
 
Contact Steve McClellan at 401 W. 11th St., Tama, IA 52339 •  stmccle@mchsi.com








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