I added u to my AIM account, i dont use it much but i added u...If it knocks, find a good used engine, their cheap and abundent...These things are worth rebuilding, i rebuilt mine for like $350 but i did all the labor...just had a machine shop bore it and do a valve job, i reassembled it...yes the Onan i feel is the real work horse..but a tecumseh can out work one if it tuned up right...Remember you just cant drop in any motor, the sears like yours the clutch mounts to the motor so you have to fab something up for that..hit me up on AIM and ill chat with ya their..

there is one engin i can think of,that is the hatz diesel,i know they make a 10 hp,a new one will be $2300,not cheap,but i hope this helps.

Careful with the diesel you swap in there. The transmissions are rated for the engine and a higher horsepower diesel is going to have enough torque to thrash the transmission in short order. The old HH120 is one of the most robust engines around and will last just short of forever if properly maintained. Mine had roller bearing mains and still had good compression after 25 years of hard use. It's only problem was the exhaust valve hanging open under very heavy load. At the time I worked for the foundry that made Tecumseh crankshft castings and could buy an engine for cost, so an OHV, balanced 18 was cheaper for me than rebuilding the 12. I gave the 12 away, the new owner fixed it up and it is still soldiering away on a log splitter.