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

[mikereid]

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]

Ouch. where did the broken piece go ?

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

 

[runningbird]

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

 

[Tig]

Any pics of the cylinder wall?

 

[mikereid]

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]

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

 

[Tig]

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]

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]

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]

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