this is the rear of the right piston of my gt350. the small end bearing was bone dry. on the left piston the markings are nowhere near as bad and the small end bearing was oily. there are no marks whatsoever on either of the barrels. i've never seen damage as bad as this before - certainly never on an engine i've built, therefor i can't comment on the cause or the cure. my first thought was overheating due to a lack of oil, but why was the right side far worse than the left? why was the left small end bearing getting oil, but the right wasn't? any suggestions would be most welcome. there's no point buying new piston kits until i know how to cure the problem :whatever:
cheers, gil.
right 64mm piston:
(https://i.postimg.cc/kMh8mK8v/seizingornot.jpg) (https://postimg.cc/jCPC6WMD)
assuming the bike is still on the pump, verify the line to the right is intact and not blocked, or cracked. do a pump test, especially the one to the case itself (if i remember correctly) the line splits into 2, one to the case, the other to the intake.
Usa a good dial bore gauge to measure piston the wall clearances, might be too tight.
I always wash cylinders in brand new solvent and use white paper towels with light oil (I use Marvel oil) on it to rub on the walls until you get no discoloration of the paper towel, in my case the Marvel Mystery oil is bright red, I rub until so I don't see any darker color, then I know for sure the honing grit is removed from being imbedded into the bore during the honing process.
Check for a high float level on the carb or bad needle and seat that is rinsing cylinder with too much fuel.
Chuck
thanks for the replies - all good advice ;D think i've sussed the problem out. with the top crankcase off and oil tank connected, i got my battery powered screwdriver and used it to drive an old tacho cable. opened the oil lever on the pump and pulled the trigger. result! oil flying out of the left side, but it got to the top of the hole on the right side, then went back down again. looks like a bad nrv. i changed the oil line for another one and tried again. this time oil is coming out of both sides. so 99% sure that was my problem, the non return valve wasn't doing its job. oddly enough, in all the years i've been building gt engines, this is the first nrv failure i've come across. have i just been lucky? :wave:
cheers, gil.