kick start lacks compression and bike is rolling in gear

[blakedonald27]

Just yesterday I was riding my bike without a problem Then I let my cousin go for a ride and he says it just cut off on him Come to find out he was shifting without the clutch Now the bike has barely no compression in the kick start I can pull it down by hand Also the bike is rolling with little resistance while in gear I took the spark plug out and there is a little air coming from where it was WHAT COULD THIS BE

this is a yz 85

 

[sharky243]

Take the pipe off and have a look at the piston and cylinder. Have someone push the kicker down for you while you are watching. If the piston is still moving up and down the cylinder, chances are that your engine is blown. If your piston is NOT moving with the kicker, you may have some issues in the primary side of the case. (clutch side)

 

[blakedonald27]

I bought it to a shop and i believe it was ridden without any cooling fluid. He is still in the process of taking the top end apart for further inspection but said it could be that it ran hot and may need a new top end. the guy I got the bike from said it was bored to 100. so how does this effect the piston kit that i purchase? or will the guy at the shop give me this information upon further inspection?

Thanks for your replies!!

 

[sharky243]

You can't bore the cylinder oversize because they are a plated cylinder. You can re-plate the cylinder, or have a sleeve installed. If the guy told you it was over sized to a 100cc, then he most likely had a big bore kit installed. You or the shop will have to measure the piston and the cylinder bore to find the correct size, then locate an aftermarket piston that fits the cylinder properly. Wiseco, JE, Pro-x are good pistons. They might make a piston to fit your cylinder. Try to find out what brand of big bore kit was used. You can get a replacement piston through that manufacturer as well.