Help! Low compression!

jhwnissan · Post by **jhwnissan** » Tue Jul 29, 2008 8:52 pm

I only have 65psi compression on my 85 spree! When I bought it a few days ago it was said to be freshly rebuilt. I ran premix through it to ensure proper lubrication but I suppose it had some straight gas still in the carb and had been run a bit before I bought it. Oil pump seems to be primed now but the low compression really worries me. Could this be a reed issue or a piston ring issue? It didn't seize or anything, just putted out and stopped running. Now it will not refire. Please help with any suggestions.

Josh

keithw · Post by **keithw** » Tue Jul 29, 2008 9:07 pm

Rings is about the only choice. Pop the jug off and take a look. "Rebuilt" can mean anything from taking it apart and reassembling to a bunch of new parts and machine work. With any luck the cylinder just glazed over and a a quick honing will allow them to go ahead and seat.

keithw

jhwnissan · Post by **jhwnissan** » Tue Jul 29, 2008 9:22 pm

How will i know if just the rings are bad? I just pulled the head and the piston and cylinder looks fantastic.

Josh

jhwnissan · Post by **jhwnissan** » Tue Jul 29, 2008 9:39 pm

crap.. nevermind.. hairline crack in the piston, i took it out and the bottom just fell apart. Amazing how fragile they are. Anyone have a new or good piston and ring set?

Josh

keithw · Post by **keithw** » Tue Jul 29, 2008 10:05 pm

That will do it. Stock and .25mm are both available from several of the online bike part sellers. Bike bandit and cheapcycles come to mind. If it is an oversize piston it should have a number, like 25, stamped into the top of the piston. Measure the bore. It might be oversize and a stock piston put back into it. That will allow the piston to rock and possibly break the piston.

keithw

justinnielsen01 · Post by **justinnielsen01** » Tue Jul 29, 2008 10:46 pm

your rings are probally still good then you just need a new piston

jhwnissan · Post by **jhwnissan** » Tue Jul 29, 2008 11:40 pm

I'm gonna call around and see if I can't find one. Hopefully I can get it all put back together without any problems. It took quite a while to disassemble the motor. I still need a gear puller for the part that charges the battery.. the dyno? Not sure what it's called. It's stuck steadfast to the crank. I'm gonna go over the whole motor tomorrow when I get home from work. Maybe I can stop by a dealer before the weekend and do a rebuild. Does a motor that is being rebuilt need some rebuild grease like on a 4-stroke? It would only make sense to me but this is my first time having to rebuild a motor like this. I love how simple it is, but hate to make a rookie mistake now that I've located my compression problem.

Kenny_McCormic · Post by **Kenny_McCormic** » Tue Jul 29, 2008 11:42 pm

When rebuilding any motor I just give everything a good coat of 30 weight.