Hello all, my first post. Looking for expert advise on a matter I'm having. Bought this bike used and the previous owner just installed a B&B 351 kit and and decided to sell cuz of a top end noise created after the install. Turned out a shim in one of the exhaust valves was the issue. Seeing this lead me to think I should tear this down and inspect his work. With no miles being on the new kit, there is concerning wear on the front and back cylinder wall and piston skirting. Any ideas of what / why can cause this so I don't put it back together and make matters worse. Id like her to last a while for a daily rider. Also I'm shocked these don't have wrist pin bearings!? First bike Ive ever seen without one

 

IMO, looks normal. It's an engine, it makes noise and things wear.

 

Thank you and appreciate your input, I agree engines wear but from just starting the new kit up a few times and never riding it the cylinder should not have a wear mark like this. I've rebuilt a lot of engines and would see this on a few thousand mile cylinder, not a few minute one.

 

I agree with OP, but I don't build engines for a living. It could be they rode it pretty hard and didn't break it in properly for the first....100 or so miles. At least when I bought my Nissan Frontier, it said that if proper engine break-in wasn't followed it would case excessive wear and reduce engine life expectancy...this kind of fits that bill even though it's not a truck, but same concept.