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Was it bored over without chamfering the port?

no its nikasil. std bore. looks like it had low hours,, the ring locator pin was pushed in .. so oem piston failure. odd, i imagine it was spinning high and on shitty gas. there was defiantly some water somewhere the good side had a milky oil ring around the top of the cylinder. ..

FYI Orange ENGINE ENAMEL DOESNT WORK ON SNOWMOBILE PIPES ,, has to be high heat, header or bbq paint.

so the piston that blew was OEM, the one that lived was SPI. who knows how long either piston has been in there , i already ordered OEM pistons, a new cylinder, gaskets,crank seals and reeds,, so we'll see how she goes.

I,ve rebuilt a lot of engines over the years,.
OEM in most high perf is way to stay, Wiseco I have used in a lot
of engines, never a issue when breakin is done right and engines
are warmed properly before w/o running,I,v only tried SPX pistons
In a couple of engines,smaller, under 80 hp, ok, over 100 hp and if run
Hard, had failures.
Your call,.good luck

Looks like ring play got excessive, how where skirts? If slap where there also
Would explain failure. Also looks lean , check pto seal, change seals , your a
Most there anyways, good luck

there was some detonation on the piston crown, and it was the original piston with 4500 miles on it so i imagine it was due for a rebuild, and carbs are dirty. (ran lean) im replacing all gaskets, crank seals, 2- oem pistons,wrist pin bearings, 1 new cylinder, ill re build the carbs and drain the gas tank to make sure its clean, and hope for the best.. then i want to re-build my f7 sooner than later to avoid this happening again

still waiting for a cylinder and a few parts, i guess im using spx pistons, and have to wait for seals as the place i ordered parts from didnt order a full gasket set like i asked for, or oem slugs GRRrrrr figure ill throw a PTO crank bearing in it since im waiting for parts anyway. we'll see how she goes.

next project ZL 500 for the gf, needed a rear suspension (Found one) and wasnt running on 2 so i'll have to open er up. .............talking about the sled

also had carbs apart,,,, they were spotless, further inspection revealed a bad crank seal. poof. its an ash tray . re jetted 2 sizes up (270) stock was 250's seems low but that's what it asked for. common parts

my reed valves got lost in the mail,:confused: so i have to wait to put the top end on, i have the bottom end together, :be:



and i have everything else