engine swap

[tonymsanchez]

I own a 638 RL yard machine ,with a formula 13.5 hp, tecumseh motor. what kind of motor can i swap out with. I heard watch out cause of need to make sure of same kind of mounting bolt pattern

 

[Scrubcadet10]

The main thing is mounting pattern, and crank shaft diameter and length.
There is a website (smallenginewharehouse.com) and you can select your specifications to find a replacement engine.