Best way to rebuild a k301
 

I have a 123 hydro with the 301 12hp and two years ago I restored and rebuilt the motor but it never ran right. I replaced the generator, points, condenser, piston, rod and rings, lapped the valves, but before I put it back together I was young and stupid and I did not understand compression release and increased my exhaust valve gap to stop it. I restored the valve gap but it still did not even start. I have decided to rip the motor out and do it completely right. I checked the bore and it measured 3.485 all the way around with it honed. And when I took the motor apart the first time I lost one of those adjustable plates for the governor and made one which made it mow with a unstable idle. Currently I ordered a new governor assembly, ignition coil, and a carburetor rebuild kit. I want to purchase a complete rebuild kit with gaskets and all. I have mixed feelings of replacing the rod, piston, and rings but they didn't even have 20 hours on them,but when I tried to start it in storage today when it cranked the dipstick shot up 2 inches with each rpm, and when it did run it would pop up and down so I had a spring from it to the generator keeping it down. Would I want to replace the governor gear while in there? I had a couple tablespoons of oil leaking from the valve cover breather hole as well. Any help would be much appreciated. Thanks

How did it run before? Me-I would dissemble,take block and crank to a machine shop to measure. Reuse piston and rod if good and fit spec. Rings/GSkt is 30 bucks
Carb clean and bush throttle shaft.

Not long and not very good probably 10 hours with major blow by but I recently found out that someone bored it out for a 14hp piston

If you have a straight true bore and the proper piston and rings- it should work fine with the 14 hp piston. You could also have it sleeved back to std bore if you'd like.
Obvious there is some issue, without complete dissassembly and inspection it's hard to pin point. How did you measure the bore? 3.485 is not correct. Bores are 3.25, 3.5, 3.75 for std bores. Add 0.010, 0.020, or 0.030 as needed.
What style piston is in the engine? Is it round or a Mahle pston?

Michael

I tore the motor completely apart yesterday and measured it, and it looks like it is a 14hp piston but it has not sliding friction in the cylinder whatsoever ever