Triumphs have iron cylinders.....I could never determine the cause other than detonation could produce enough heat...This is a dual engine land speed racer, the seizure happened while testing on public back roads.....It's been raced since then without piston problems..DCal wrote: ↑Sat Jun 16, 2018 5:18 pm One of vintage racing Triumph bike engines had a slight bit of scuffing......Forged piston in a 2.9 inch bore with .0055 clearance that was never a problem previously...I believe it was a fueling problem leading to detonation...
I have seen this many times. When you see the ring lands scuffed like this it is lack of lubrication. And that usually is ring butting which scrapes all the oil off the cylinder walls. You can just imagine the heat that's building up in the piston, rings and cylinder walls. If the scuffing were on the skirts only it would be an indication of a clearance problem.
If there was a fueling problem causing a lean condition engine would become hotter and that could use up the available ring gap and more. If it were a flooding situation it would wash the oil off the walls and the rings would be ruined by vertical scratches which would cause loss of sealing to some degree. I would think that a properly designed piston with .0055 clearance in an aluminum case was more than adequate.
I have found the full floating pins seized in piston after a heat related seizure...
