88 EZGO Marathon 2 stroke help w/compression
 

I know it has been awhile. I have a 1988 marathon. We rebuilt the engine. Took it to a machine shop and had them bore it and fit a .50mm piston. He also shaved .0018 off the head. The machinist is an old timer that said he had done hundreds of 2stroke Robyn engines. Anyway got injured in a dirt bike accident and the engine sat for over a year. I just put it back in the cart and compression is 90 psi both ways. Battery was a little weak put the jumper pack on and got 100psi. I was hoping for at least 140psi. Any thoughts.

Re: 88 EZGO Marathon 2 stroke help w/compression
 

I replaced crank bearings, both crank seals, and all gaskets. I tried squirting some oil in the cylinder no change in compression.

Re: 88 EZGO Marathon 2 stroke help w/compression
 

Did you test it with the throttle open?

Re: 88 EZGO Marathon 2 stroke help w/compression
 

Yes with throttle open and closed

Re: 88 EZGO Marathon 2 stroke help w/compression
 

Is the piston in with the hole facing the intake side, and the rings with the bevel side up?

You may also have to run it a bit for the rings to seat, and then get a good seal.

Re: 88 EZGO Marathon 2 stroke help w/compression
 

I already thought of that I guess I better check it when I get home from work tomorrow. Thanks.

Re: 88 EZGO Marathon 2 stroke help w/compression
 

Yes piston is in with hole facing away from exhaust port. I couldn't tell if the rings were bevel up. I am sure they are I always do them that way on 2 stroke dirt bikes.

Re: 88 EZGO Marathon 2 stroke help w/compression
 

http://www.buggiesgonewild.com/album...ictureid=24013

This is a picture of my piston through the exhaust port maybe you can see the rings and tell if the bevel is up. Thanks.

Re: 88 EZGO Marathon 2 stroke help w/compression
 

Bevel is on the inside, so can't tell. If it went in easy, it is right.

140 compression is with a warm engine. I would run it for a while, and then check again after it breaks in.

Re: 88 EZGO Marathon 2 stroke help w/compression
 

Okay thanks.