Viper low compression, piston and ring options

S

sx600

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Aug 10, 2004
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I have a 2002 viper I bought brand new. 6500 miles, bone stock everything (exhaust, needle clips, jets, etc). It's ran perfectly all these years. I did a compression test on it and found 112.5, 112.5, 95 PTO side - cold without carbs on.

I haven't opened it up yet, but before I do I have seen most people on here are stating to stay with stock OEM pistons, rings, bearings, etc. Most of those posts were from the 2000's. Has anything changed now? I can get a full set of Wiseco parts with gaskets for $660 (and there are cheaper options). The OEM parts are well over a grand and would still need to use aftermarket gaskets as they are discontinued.

What are people using these days for the parts?

On a side note, the mileage was greatly reduced last season - down to about 7 mpg and the plugs were very fouled wet. I went in and did all the carb work per this site - and then found the compression issue. It would seem all of the issues could have just been the compression issue.
 
Could be worn jet needle and or needle jets. They vibrate through their life and wear making more fuel pass through. That problem does normally come on slow though. It is never a bad idea to change them if you can find them still.
 
sounding like it might need a set of reeds with that low milage. it could also be a split diaphram in the fuel pump.

usually refresh is at closer to 10000 mi. at that milage, just a gasket set and rings is probably all you need. vipers had staggered compression with (i think) pto cyl always measuring lower. some compression testers read lower than others. have you tried it with oil in the cyls as well?

as to parts, had no issued with the aftermarket gasket set we used on my brothers 02 but we did opt for the opticool head gasket. we did use spi pistons on his as his nuked the connecting rod bearing and we had to find a crank assembly. there was an issue with the wrist pin connecting rod bearings on the 02 vipers as his was running on the ritch side when it went down. still mad at the guy that screwed us on the crank on it at the rebuilder. scrapped ours to fix someone else crank as brothers failed in a not common cyl.
 
I checked the jet needle and jets they looked fine. The reed had a tiny bit of chipping on the ends but didn’t seem to affect the closure. I replaced them though. Replaced all the gaskets in the carbs too. And orings.

Pilot jets were plugged even though I cleaned them prior to last season. So they had less than 800 miles on since they were cleaned.

I’ve seen a lot of posts about just doing the rings if the pistons and cylinders look ok. I hate to remove the head and go through all that work if only rings won’t fix this issue though.

Then one gets to the bottom end. Since I’m in the top end do I remove engine to have the crankcase bearings and seals redone? At this mileage? I would have hoped this would have went over 10k before doing all that!
 
all that work was just done so it hasn’t been ran yet. If the rings are bad I assume that would foul plugs and cause the mileage issue too right?
 
I looked at the emulsion tube for were as I know that can let more gas through. It looked fine to me. Only things changed are gaskets, o rings, and reeds.
 
Did you have a new one to compare it to? They don't necessarily go oval.
I've found that they are the main culprit when it comes to fuel milage getting worse with miles.
As far as compression goes, you should use a leak down tester to further confirm if it needs rings or not.
I tend to agree with maim that it shouldn't have to be pulled down yet.
 
bottom end should be fine. the only issue with them that i was aware of was the wrist pin bearings in the connecting rods. they where common back then as that bearing was shared through a few sled brands that had the same issue.
 
I don’t have a new one and they are discontinued. So buying a used one who knows what you’re getting right?
 
At a min I’m doing the entire top end - just not sure what pistons I’m going to use. Still debating on pulling the crankcase.
 
I pulled the pto cylinder today that had 95 psi. No scoring, no big lip at the top and can still see cross hatch marks. I think all pistons are just tired but not damaged, Some studs are really rusted though.
 

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