Engine code question
 

I looked at the sticky, but didn't quite find my answer. I am buy a 125cc engine with the stamp code, FH157FMI, on it. I know that the I represents 125cc..but the 57 should represent 57mm bore, which is 150cc. The engine is a Lifan style. Anybody else have this code? I plan to tear it down when I get it. Just wanted to know the size to order some parts. Thanks John

Just looked it up.and you can get 56.5 bore x 48.8 stroke pit bike engines. My guess would be, so they can use the same engine for a 150 using a longer throw crank.