i have a 1996 bibear 350 4x4 that i have recently had bored now when this motor is at an idle for more than 3 or 4 minutes the exhaust pipe turns cherry red. the valves were lapped in and seated. can anyone give me an idea of what is causing this? The jug was taken to a shop and i took a 20 over wiseco piston with the jug and the man that bored it said he had to go one size bigger than a 20 over piston so i am assuming he bored it 30 over. would that cause the exhaust to get hotter or should i be looking for another problem?

 

How much running time is on engine now? Is engine quite?

 

there is about 3hours on this engine total.

 

there is about 171/2 hours of run time on this new piston

 

Okay thats fine.Did the guy bore cylinder to match piston? or did he put an 30 over piston into an 20 over cylinder? How much cylinder and piston clearance does you have? is bore straight?Did you check end gap when you install piston? Can you hear any scraping noises while engine is running?