New piston in a scarred cylinder

My buddy has a 95 yz 125 that needs a top end. At the moment he's unemployed and as always he's a cheap ass. The cylinder needs replated for sure but he says he just wants to put a piston in it and ride. I told him that's stupid but I don't really know what to tell him to change his mind. I told him the bike would run horrible if it ran at all. Would it even run?

It depends on how scored the cylinder is.  I have seen some messed up bikes run good.  It is a gamble for sure.  If there is enough left of the cylinder for the ring to seal then it should run ok but it will not last long. 

Yes , it would run ... But it can only get worse

If his sleeve is worn out, as in the diameter is larger than stock, he will get skirt slap, the piston will crack at the skirts and could even blow apart and ruin his case.

It might run depending on the severity. I had a overhung piece of plating (in a plated cylinder) that chipped off and cut a .0010" gouge in the piston. The bike ran good with no loss of power, but did get tough to start. Only had 20 hours on that cylinder and piston when it happened, since had it replated with a new piston.

But I can guarantee that he will destroy the piston and waste $. In my opinion why ruin a $100 piston when you can put that $100 towards the right repair

Try and tell him that the piston can shatter and drop into the case, which in turn can cause the crank to suddenly stop, which in turn can punch the connecting rod thru the cylinder, causing many $100's of dollars of damage. He would not be wise to not do the repair correctly.

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