Rebuilt top end-had good compression, now I don't????
 

1998 Polaris Xpress 300, 2 stroke

Rebuilt top end, piston, rings, and gaskets. Motor was rebored and honed correctly. Put added oil with gas to help break in (done right). Checked top end compression after that and compression was strong. Still no fire. Great spark. Rebuilt carb, cause was getting gas in crankcase. Then couldn't work on it for a month. Got back to workin on it and changed out the clutch side oil seal cause it was leaking out of the crank there I noticed after doing the rebuild. Figured it was ready to go after all that. Went to start it yesterday, it turned but no attempt to fire at all. Rechecked the compression, and it was way to low???????
Any suggestions????????? Thinking I'm gonna have to retear into the motor, only this time the top and bottom.

Thank You
Kelly

has it run at all since rebuild?? sounds like maybe the rings didnt seat correctly. you could try a leak down test as that will tell you alot more then then only a compression check. ive never done a leak down on a 2 stroke, but you would have to make sure the piston has covered all the ports in the sleave...

Rings

Crankshaft seals replaced?. Old Polaris Tech says leaky seals #1 cause of low compression in 2 strokes.

One thing you must realize about a 2-stroke is seals go out for a reason, for instance it is most likely caused from bad crankshaft bearings. Allowing the crank to 'wobble' inside the cases.

A new seal might work temp. but if the root cause is not fixed it will break down again.

It would be best to do a 'complete' bottom end rebuild, including all bearing/seals.

Question-
Before I went to change out the seal, I tried to wiggle the clutch to see if there was any play in the crank shaft. It wasn't rock solid tight, but it had an very very minute wiggle. Is that normal, should it be rock solid tight- absolutely NO play, or is that indication of something?

Next Question-
Do you think I did further damage now that I don't have compression again? All I did was try to start it, it never did fire up.

Thank YOU!
Kelly

zero play

I doubt you did any damage trying to start it, the new top-end should still be fine.

Even a minute wiggle in the crank indicates bearings are bad! Probably havent hurt the top end,but bottom end needs to be addressed! Not just the 3 crank bearings,but since you would be down that far,a rod kit also! I've been snakebit in the past and wont guarantee a top end only on customers machines,because I seen money go down the drain! At least maybe you caught it in time and do a complete rebuild. Dirtjunkie gave you the advice I give most customers on the 2-stroke machines! Four strokes are a lot more durable on getting by with just top ends,but not 2-strokes. Keep us posted OPT

Thanks guys-
Why is it you think I lost compression on the top end though? Someone did mention rings might not have set right. It was real strong right after the rebuild. Will I also lose alot/some/none top end compression with a sudden change in low end compression?
Thanks
Kelly
I will deffinately keep you all posted til the end.

Possible rings may have stuck in piston if cylinder didnt have enough lube when you installed piston,plus if crank is out of true(bearings, rod play) can do the same thing and put unequal pressure on the piston causing rings to stick in their lands. Bottom end problems can take a new top end out quickly,BUT since your machine hasnt started,probably can save rings . OPT