If yours is a single cylinder and looks like this. Just re-ring it, how hard can it be?
Here,
Rebuild for some BRIGGS and STRATTON ENGINE 10, 11 ,12 , 12.5 ,13hp | eBay
As long as it is a iron liner engine. Will have a I/C on the flywheel cover, stands for industrial/commercial.
If it is not, it is not worth rebuilding.
plenty of junk tractors around with good motors. i would buy a cheap one and switch motors.
Briggs and Stratton 16.5HP OHV
Model 313777 Type 0163E1
In addition to burning plenty of oil:
It's also got a broke front left motor mount. Motor shakes loose on the deck every once and a while. It's got 3 other mount bolts, which I have tightened or replaced more than once over the last 5 years.
I have tried valve adjustment, but it builds too much cylinder pressure. I have run out of adjustment without leaving the exhaust valve partially open. If I shut it off hot, it won't restart for 30 minutes.
It used to like to break intake push rods, but I fixed that by installing an exhaust push rod for the intake valve. They are same length. Seems the exhaust rods were made of steel, but the intake with aluminum? Or some cheap pot metal?
Needs a helicoil to keep the exhaust pipe from falling off and burning the spark plug wire below it. Pipe is held on by 1 bolt instead of 2. Have to regularly check bolt tightness
MTD built the tractor for Statesman brand. MTD Model 678. All the safety stuff developed shorts, resulting in no starts. Electric fuel pump wire runs under the engine from right to left. It's vulnerable too. I essentially rewired the tractor to get rid of the safety features and shorts. It has toggle switches for fuel and ignition with push button starter now.
Mowing deck hits pulley when raised out of mowing position while moving. Makes sparks.
Just getting tired of the tractor. It's like a Chrysler Concorde I had. It would run and keep going as long as I kept fixing things. Finally, I got sick of the car and junked it around 190000 miles. The mower is the same way. Further, I'm afraid it I buy another B&S that fits the deck, I'll end up with the same problems.