951 Compression

[seadooman]

I was having fuel/oil come out the exhaust and it would not idle or run right. So I checked the compression it was 90psi in each cylinder. I micd. them and they came out to be 88.30mm - 88.31mm. This has the 88.16mm piston in it. The cross hairs still show in the cylinder can I just replace the rings and it be fixed. Someone said it needed to be 9mm dfference and another guy told me it needed to be .005" which is 13mm. Which is correct?

[dsolie]

Re: 951 Compression

Check it with another gauge... 90psi in BOTH cyls sounds like your gauge is off. 90psi is WAY low.. 130 is stock range.... but I have never seen BOTH cyls read low unless there is a major issue with both pistons, like meltdown. That would have been visible when you pulled the head though.

88.16 is stock bore piston. 005" clearance is std. If you are already way over that, then you may need to go 1st over on the pistons.

[seadooman]

Re: 951 Compression

i have 2 other bikes they checked out right with this guage. Can i get away with changing the rings. What happened is i cranked it up without the airbox on it and was running it and it ranaway on me never havng this happen to me before i cut the fuel line to shut it down. Now i learn that i should pulled the choke. The bore size is 88.30 which would be be .01mm overbored if everything is correct

[dsolie]

Re: 951 Compression

Yes, you can change the rings. But I still don't think that will solve the entire problem. Since you have to pull the cyl to change the rings. Do that first so you can properly inspect everything.

[seadooman]

Re: 951 Compression

i already had pulled everything apart and it looks good the only thing i can thing of is the battery was low. giving me low compression

[dsolie]

Re: 951 Compression

yup.. that'll do it!

[seadooman]

Re: 951 Compression

thanks will let you know if that fixed it.

[seadooman]

Re: 951 Compression

Charged battery and I put the new rings in ran a quick hone through it. Put it back together have not torqued down the bolts yet but i have tightened them. I got 123 psi from both cylinders will that go up after i torque down the bolts, install exhaust back on, and install carbs.

[dsolie]

Re: 951 Compression

123 is not too bad.. I have seen OEM stock units blow 130.

It might go up a little...