YM2000 piston. I think I found my running and starting problem

mikereid · Jun 20, 2009

Here is a picture of the piston I pulled out of my engine today.

The rings looked really good but part of the piston was broke inbetween the top two rings.

I think this may be my hard start and lugging problem when taking off from start.

What are your opinions?

Willl · Jun 20, 2009

Ouch. where did the broken piece go ?

Was there a comp test done before tear down ?, results ?

runningbird · Jun 20, 2009

you found the problem...were the pieces in the oil pan? How do the liners look?

Tig · Jun 20, 2009

Any pics of the cylinder wall?

mikereid · Jun 20, 2009

The piece was still in between the rings, in place just loose.

There was no wall scaring at all. I could not believe it myself if I did not see it.

I did not do a compression check before hand.

runningbird · Jun 20, 2009

that makes sense. I would still give the liners a once over. new rings and bearings and you should be all set.

Tig · Jun 20, 2009

I have reused bearing in a simlar situation. Don't forget the obvious, a new piston.

What ever you replace be sure to check the old part for any indication that they are not original size (eg a .010 mark on them) On the bearing it would indicate that the crank has previously been reground. On the piston, then the cylinder has been over bored. I think even the rings can be marked near the gap.
I forgot to check once and had sloppy bearing fit on reassembly.

mark777 · Jun 20, 2009

Is it possible that the piston broke during dissasembly? The break and casting surface looks very clean to be broken for any extended run time....Just playing the devils advocate here.

Mark

mikereid · Jun 21, 2009

The only reason I think it has was broke before I got it is that there is scoring on the side of the piston like it was pushed over to one side.

See the pics one of each side.

tommu56 · Jun 21, 2009

I broke one it looked just like yours when I didn't ream the ridge off the cylinder (young and naive) I just hammered it out. then I reamed the other 7on that motor and they slid right out and reamed then first to get new pistons back in.

tom