i almost am ready to buy a fourstroke

[Eddiesanders250]

so about a year ago i replaced my top end, i had it bored at a small little shop because i was over at the coast riding.. So this piston recently seized while someone else was riding my bike. I figured it was maybe a bad bore or bad piston, (cheap) so i just replaced the top end again with a wieseco and bored at napa so it shoould be a good bore and before i even got through break in it seized again. I was running really rich so i did not lean it out. What could have caused this. it was running perfect when i was breaking it in. it would stop running every once in a while so i checked the plug and it was black and wet so when i replaced it it ran perfect again. Then one time when it felt like it lost compression it would not start again. I pulled the top end off and it had deep scratches and the front of the piston was burnt. what the heck?

[deathman53]

you got something else wrong?? crank bearings, rod play, metal shavings/chunks in the crank case??? There is something else wrong.

[86250rrider]

ok....heres is what happened: the guys at napa didnt know to relieve the exhaust port! that port is narrow and heats up and swells causing excessive wear in that area. ill bet your rings are notched or worn in that exact spot....arent they?thats why you should always take you jug to a guy that is a motorcycle or better yet,a two stroke enthusiast to get done.i overheated a jug that was relieved and it still swelled enough to whip the rings! also....dont add extra oil in your mix for break in...it leans out the air/fuel mixture. check them rings and let me know;)

[wilkin250r]

Originally posted by 86250rrider
ok....heres is what happened: the guys at napa didnt know to relieve the exhaust port!


I could see this as a very real possibility.

Especially when you say "it would stop running every once in a while so i checked the plug and it was black and wet so when i replaced it it ran perfect again" The motor heats up, and the exhaust port starts to bind it up with increasing pressure and friction, until it eventually kills the motor. A little time to cool down would relieve the pressure and binding, and allow the motor to run again.

[86250rrider]

Originally posted by wilkin250r
I could see this as a very real possibility.

Especially when you say "it would stop running every once in a while so i checked the plug and it was black and wet so when i replaced it it ran perfect again" The motor heats up, and the exhaust port starts to bind it up with increasing pressure and friction, until it eventually kills the motor. A little time to cool down would relieve the pressure and binding, and allow the motor to run again.



yep....he was experiencing partial seizures. hell....maybe the sizing or clearances were wrong but im sure they followed recommendations.did you give them the box and piston didnt you ?if it was a forged piston....making it a little tight combined with to short of a warm up will get you to. im running a wiseco now but i really prefer a pro-x or cast piston.because the cast piston can be fitted tighter and have almost no thermal expansion. DONT BLAME THE 2 STROKE ENGINE......IT WAS MAN WHO SCREWED THIS ONE UP . a 2 stroke engine is very reliable a cranks out huge huge power for its size............."so understand it ....embrace it.......and let the good times roll !!!! " :D

[86 Quad R]

another thing that most average shops dont know to do and will kill an engine is to chamfer the ports. a fresh bore with sharp edges on the ports will ruin a piston and rings.

[86250rrider]

ABSOLUTELY.......i forgot that.the guy that does my bores knows better....his kid raced. but the guys at napa.......who knows ?:rolleyes:

[wilkin250r]

Originally posted by 86 Quad R
another thing that most average shops dont know to do and will kill an engine is to chamfer the ports. a fresh bore with sharp edges on the ports will ruin a piston and rings.

I think this would be a lot LESS likely. It's almost as common knowledge as honing. Just about anybody that gets near a boring machine knows to chamfer the ports.

But not everybody knows to relieve the exhaust bridge.

Of course, I've seen a few shops that expect YOU to chamfer the ports yourself, or else they charge extra for them to do it. But usually if this is the case, they are very clear about it, they make SURE you know that the port edges are untouched.