i went full retard and forgot to put the air filter on the other day when i had the engine running and it sucked some little metal bits in and scored the cylinder walls beyond just honing them. i cant find any place that sells oversized pistons. is there a place that does sell them? or do i have to get a new cylinder assembly?

 

try ebay i have seen pistons and cylinder assembly on there recently and not exspensive

 

i got another question. when i go to break in the new piston rings, does the engine have to be under load for the rings to properly seat? or does the engine just have to running slowly through the rpm range?

 

Load. idling and no load is actually probably the worse way to break it in. About half the engine builders (OEM's, Haynes, ASE) say baby the motor for 500 miles before romping on it.
The other half (F1, NHRA, NASCAR, etc) say drive nice until the motor is at operating temperature, then rod the **** out of it to get everything seated. I have always used the second type when building my engines.

 

Same here.. I usually let it warm up to operating temp while checking for oil pressure, leaks, weird noises, etc. After that I'll go do a series of WOT runs up to maybe 80% of redline, let off & coast down in gear, and repeat. Change the oil after that and drive it. Accelerating hard and then letting it coast down in gear does a good job of getting everything seated quickly.

I would definitely not try to break in new rings by idling/revving the motor.. being under load is what seats the rings against the cylinder walls.

 

alright. so the scrapes in the cylinder wall in cyl. #2 are still big enough that they catch my fingernail pretty easily after honing with a positive pressure hone. is there any way that i can repair the cylinder walls without having them bored out? cause i cant find over sized pistons anywhere and all of the cylinder assemblies i see on ebay arent in very good condition

 

The only thing that I can think of would be to sleeve the cylinders, but I don't know if it's possible on this engine or if there are sleeves available that fit. Might want to check with a machine shop unless someone else knows of a better idea..

 

well someone suggested taking sleeves out of a good cylinder assembly and putting them in mine (or just the one) i was also thinking about TIG welding the scratch and having the machine shop use a bore tool to make it flush with the rest of the cylinder or would that be frowned upon?

 

While it is possible to do, a lot of considerations need to come into play.
One, whenever you weld it distorts the metal and causes it to flex and move. You would have to remachine both inside and out to make sure it was perfect.
Two, are you going to x-ray the weld to make sure it has perfect penetration? can you imagine your weld breaking off during a heat cycle and ignition event?
Three, the weld is usually significantly harder than the metal was before, this will cause uneven wear on the rings and the piston itself, basically wearing another groove into the piston.
Fourth, Calling Wiseco or JE is fairly easy, If you give them the stock piston specs and explain you need one a little larger they might have something from another engine that would work. My custom pistons from Wiseco in .010 over were not that much(but it was back in 2001). They will need a lot of measurements, ring sizes, wrist pin size/offset, bore size, etc. I just sent them a stock piston back then and they made me the new ones from it.

From the sound of your wall damage you would probably need to go .040 over to be out of the damage zone.


Fifth, never go cheap on your engine build in bike. You blow your motor in a car and you can still drive it out fairly easily. You blow your bikes motor mid corner and it locks up, you can kill yourself or others. I had a friend who had a built CBR929. He knife edged the crank himself(not balanced). Mid way through a corner the crank broke and seized his motor. Back end locked up and he slid into an on coming semi truck. He lived, sort of, in a coma, for about a year before his family pulled the plug and he passed away. This was back in 2003-4ish.

 

Re sleeving is a good idea.

On welding, while it is possible to do, a lot of considerations need to come into play.
One, whenever you weld it distorts the metal and causes it to flex and move. You would have to remachine both inside and out to make sure it was perfect.
Two, are you going to x-ray the weld to make sure it has perfect penetration? can you imagine your weld breaking off during a heat cycle and ignition event?
Three, the weld is usually significantly harder than the metal was before, this will cause uneven wear on the rings and the piston itself, basically wearing another groove into the piston.
Fourth, Calling Wiseco or JE is fairly easy, If you give them the stock piston specs and explain you need one a little larger they might have something from another engine that would work. My custom pistons from Wiseco in .010 over were not that much(but it was back in 2001). They will need a lot of measurements, ring sizes, wrist pin size/offset, bore size, etc. I just sent them a stock piston back then and they made me the new ones from it.

From the sound of your wall damage you would probably need to go .040 over to be out of the damage zone.


Fifth, never go cheap on your engine build in bike. You blow your motor in a car and you can still drive it out fairly easily. You blow your bikes motor mid corner and it locks up, you can kill yourself or others. I had a friend who had a built CBR929. He knife edged the crank himself(not balanced). Mid way through a corner the crank broke and seized his motor. Back end locked up and he slid into an on coming semi truck. He lived, sort of, in a coma, for about a year before his family pulled the plug and he passed away. This was back in 2003-4ish.