broken piston

ZoMbIeCuStOmS

ZoMbIeCuStOmS

New Member
Apr 7, 2010
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I bought another blaster from a guy a while back with a blown motor I tore the motor apart and found the the piston skirt was broken on one side the guy told me that the motor had been bored out the bike itself has a wisco piston sticker on it so i figured its a wisco piston in the motor but the problem is that I have no idea what the motor has been bored to. the cylinder walls look great and the rings are nice and shiny so i think the jug will be fine I just need an new piston. On top of the piston itself it says 200 and that is the only number I can find on the piston does that mean it is bored .20 over
 
find a local machine shop and take the jug there and have them measure it for you. if the piston skirt was broken you need to clean the crank chamber out really well. also the piston probably had too much clearance is the reason it broke so you def need to get it measured before you just go and buy a piston
 
thanks for the advice on the jug I had thought about taken it to the machine shop but and thoughts on the bore size itself?
 
no clue from your details. the machine shop is the easiest way to go. or just send it to kenoconnorracing.com he will hook you up for a great price and you will know everything is done right. I have seen a lot of people on here use local machine shops and get screwed(myself included) there are alot of little details they leave out bc they don't know or are just lazy
 
scotj77 said:
find a local machine shop and take the jug there and have them measure it for you. if the piston skirt was broken you need to clean the crank chamber out really well. also the piston probably had too much clearance is the reason it broke so you def need to get it measured before you just go and buy a piston
Click to expand...

Agreed! That piston skirt probably broke because the previous owner didn't watch the piston-to-cylinder wall clearance when the engine was put back together. The piston skirt broke when the piston slapped around inside the cylinder due to this excessive clearance. The skirt hit the cylinder wall and cracked off.

If you have a micrometer and bore gauge, you can measure your own cylinder and compare it to factory specs, but if not, let a machine shop do it and they can tell you how far oversize the cylinder needs to be bored. You can go up to .080" oversize with a Blaster cylinder before needing a new sleeve. After a PROPER re-sizing of the cylinder has been done, you can reassemble the engine with a new Wiseco piston. These are good pistons and it takes a lot to break one. In this case, the cause was likely poor machining done in the past.
 
Braaaptor195 said:
Agreed! That piston skirt probably broke because the previous owner didn't watch the piston-to-cylinder wall clearance when the engine was put back together. The piston skirt broke when the piston slapped around inside the cylinder due to this excessive clearance. The skirt hit the cylinder wall and cracked off.

If you have a micrometer and bore gauge, you can measure your own cylinder and compare it to factory specs, but if not, let a machine shop do it and they can tell you how far oversize the cylinder needs to be bored. You can go up to .080" oversize with a Blaster cylinder before needing a new sleeve. After a PROPER re-sizing of the cylinder has been done, you can reassemble the engine with a new Wiseco piston. These are good pistons and it takes a lot to break one. In this case, the cause was likely poor machining done in the past.
Click to expand...

fully agree. just you can go up to .90 over
 
Braaaptor195 said:
Agreed! That piston skirt probably broke because the previous owner didn't watch the piston-to-cylinder wall clearance when the engine was put back together. The piston skirt broke when the piston slapped around inside the cylinder due to this excessive clearance. The skirt hit the cylinder wall and cracked off.

If you have a micrometer and bore gauge, you can measure your own cylinder and compare it to factory specs, but if not, let a machine shop do it and they can tell you how far oversize the cylinder needs to be bored. You can go up to .080" oversize with a Blaster cylinder before needing a new sleeve. After a PROPER re-sizing of the cylinder has been done, you can reassemble the engine with a new Wiseco piston. These are good pistons and it takes a lot to break one. In this case, the cause was likely poor machining done in the past.
Click to expand...

good info there but i thought that they could go .090" over?????
 
Wiseco stamps the part# in the top of the piston. Part of the # is the bore size.

That said, pistons don't fall apart without a reason. Likely it was worn and started slapping and broke the skirt. Time for an overbore. Most shops want the cyl in hand so that THEY can measure it and THEY can tell you what size to buy. Even then, a good shop won't bore it until they have the piston in hand. Too many numbnuts buy the wrong part.
 
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ok so if I go .090 over what else do i need to change or should I change and has anyone done this if so how are the power gains
 
sorry dude we weren't tellin ya to go .090 over. we were just messin around with each other. the easiest way to take care of your problem will be to send the top end to ken he chimed in a few posts up from here. he will do you right. but be sure there is no debris left down in the crank chamber or that will screw stuff up bad. you want to bore your cylinder as little as possible when you bore it out to make the cylinder last as long as possible. just contact ken oconnor. go to his web site and give him a call.
 
ok then let me ask you this how do I go big bore I have a good running blaster and a box full of motor I want to build this puppy up how exactly does the sleeve work I realize these may be dumb questions for the experts but I do not know much about atv motor and much less about 2 stroke. so if I buy the vitos big bore kit 72mm piston, rings set, c clips, wrist pin, big bore top end gasket and big bore sleeve what else will I need and how do I go about it, do i just have the machine shop bore the jug to fit the sleeve and rebuild from there or what thanks for your help guys
 
I would get my current jug ported by someone like flotech, kenoconnorracing, or, wildcard. i am more of a stock sleeve fan than big bore. yes you have to get the stock sleeve bored until it is gone and then they put the new big bore sleeve in by heating the jug and freezing the sleeve to expand the jug and shrink the sleeve. then they put them together and hope they get it straight fast enough. you might as well get all the life from your current sleeve before going to a big bore.
 
unless your gana do an all out motor build a resleaved cylinder wont make as much power as a vitos 240 and not even compraded to a ct240 you dont have to get yor cylinder resleaved for a big bore u can just buy a big bore kit like this one Vito's Vitos 240cc 240 Big Bore Cylinder Piston Blaster: eBay Motors (item 190412061860 end time Sep-28-10 13:44:02 PDT) or theres a better one vitos is a decent bbk but imo they ask to muchfor them then theres the ct it uses 250r reeds instead of blaster reeds L.A.SLEEVE Store
 
Last edited by a moderator:
like i said I have a good running bike and this motor I just want to build for power I dont have a shoestring budget but there is a budget and a 560 jug wont fit the 160 sleeve kit will fit so what I am asking is, is the sleeve kit which says that it will bore it out to 240 is that worth the money or would you just steer clear of it all together and if I go that large what else will I have to do to the bike thanks again for all your help
 
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