Poor compression 340

[snowbuster]

Just rebuilt the top end on my kids 2000 340 ovation sled, the compression was 95/100 lbs before I started, which seems low.I put in kimpex pistons,rings,bearings and pins. The cylinders were spotless, so I was surprised when the compression went down to 80 after re-assembly and running for a bit. I changed the head gasket back to the original 3 ply metal unit and gained 10lbs momentarily,then it dropped again after starting. Is the compression on these machines supposed to be that low? the manual says 6.5 to 1. Or is this just a case of rings needing to go through a break in period? Any helpful comments would be appreciated.:d

 

[Rockwerx]

Did you hone the cylinders before you installed the new pistons and rings?

 

[overkill131313]

Did you hone the cylinders before you installed the new pistons and rings?

x2! I hope you did!

 

[CountryRider]

Did you get your cylinders bored out to the next size and asked for minimum clearance with your new piston and rings... when your low on compression on a machine that has been used for a while... You need to get your cylinders bored out ATLEAST .010 over, and you need to buy the matching piston and rings, and ask then to give you minimum clearance. In your case what might of happened was you got the standard size piston and rings and put it back in your original cylinders. Even if you honed your cylinders putting a standard size piston and rings in a naturally bored out cylinder (used after a while), you get high compression at first but really quickly will lose compression from doing so... Pm me.... I want to know what you exaclty did and put in it...

 

[snowbuster]

I did replace pistons and rings with std size replacements, ring end gaps were good. Took some advice to not hone the cylinders to avoid potentially damaging the nicasil coating. Maybe honing should have been done. I don't know how long the sled was sitting outside for, when I got it turning over was no problem, but suspect neglect may have been a factor. Machine only had 900 km on it. The kimpex kits may not be as good as the factory replacements either. Thanks for the responses.