I have finally worked up the nerve to tell you folks that I'm going to have to re-power my 12G. It is still running well but the smoke has gotten to the point where it is offensive to anyone in the way of where it drifts to, and it gets a little hard to see on my end too! Last weekend my wife and kids had enough and bought a 13hp Predator engine for Father's Day. I had told them a month or so ago I could probably get a different engine cheaper than a .020 piston for an HH120 (if one could even be found) and required machine work to do the job.
I am going to approach this with the intent of altering the tractor as little as possible building engine components to fit instead, like a different exhaust and air cleaner setup. It looks like the centerline of the crank will be only about a 1/4 inch higher than the HH120 and I can probably move it back slightly to make up for that. I'm sure holes will need to be drilled but I think the hood and grill will remain stock. I'm hoping to adapt the muffler and chrome shield since the exhaust port is on the same side.
My first panic attack happened when i realized the shaft on the HH120 is 1-1/8" and the new engine is 1"! I thought learning more about the lathe and mill at work building a sleeve would be needed then but doing a search, there is exactly what's needed on an ebay store cheap-19 bucks shipped and it is on it's way! Re-using the pulley is required especially with that vari-drive belt groove on it.
Anyway, i hope that this doesn't get me shunned away from here, love this site. I just am at a point where something has to be done within our budget and purpose.
I will still keep annoying everyone around our neighborhood and buying lots of 30wt in the meantime until it's not necessary to mow twice a week! With my available time I'm hoping that the tractor will be out of service 2 weeks when the grass quits growing so darn fast!