02' Viper Compression?

Yamasquaw

Yamasquaw

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Joined
Jan 8, 2005
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235
I did a compression test today and it read 90 across all 3 cylinders after warmed up . Sled has 5200 miles and runs like a charm, does this sound ok? :rocks:
 
I think I would check with a different tester?? sounds low
I think mine with stock head (before the cpr head) was @125,145,145?? not sure
 
Does anyone know what they should be at,i think i'm going to do a compression check and leak down.
 
On a cold, stock engine, 110-115 PTO, 120-125, for the mag and center cylinders. Readings will be lower with the motor warmed up.
 
Well I tried another test today (cold) and it read,pto 95 ,center 105,mag 115. Then tried a couple drops of oil in each. pto 103, center 110, mag 120. Don't want to rip it apart cause runs so well and spanks everyone i ride with. thanx for input guys
 
Yamvip......there is 5200 miles , 8320km's. And they are all hard miles too!!!
 
yes i agree,i have 3500 miles i'm gonna check it out later tonight.I'll let ya know what mines at.
 
something does not sound right with that reading.
Pull you exhaust and look inside the cylinder let us know what you see.
I just replaced rings on my SXR with 8700kms and it needed it.
 
What doesn't sound right,what he read the first time.I know if i read that I'd be buying some parts!!!!
 
New rings at 3000 miles, and you wouldn't have that problem.... Sounds to me like you need some work... 5% per cylinder variance COLD!!!! gary Oles nosboy
 
I would say neither readings sound right.
Before I replaced my rings I was reading 121 to 122 and have not checked with the new rings. I had blowby and that is why I did the rings. My compression was still ok but would only get worse and it is better to change them now before something lets go.
 
My advice . . .

Tear it down and inspect it, before it tears itself down . . .
 
compression test is not the answer

It seems to be a big misconception that just because the sled has over 100lbs of compression it doesnt need rings. Lets think about this, a 2 stroke motor takes 2 times the abuse a 4 stroke does, not to mention that piston ring seal is critical to performance. You need to do a leak down test in order to know if a motor needs rings, the amount of pres. lost in a cylinder thru leakage past the rings/piston skirt is far more important then the amount of compression it can build, but lose very rapidly. The pres. you lose past the worn rings/piston skirt is pushed below the piston and contaminates the fresh fuel/air charge in the transfer ports and crankcase. You can see this on a engine as black residue on the bottom of the transfer ports on the cylinder and on the pistons sides below the 2nd ringland, it will be all black. I have seen engines with as little as 1500 miles on them need rings, and then I have seen some with 5000 miles that are still pretty decent shape, all depends on oil run and what kind of conditions it was used in.

The second part of this pertains to quality of the oil used, if you use nothing but yamalube or some other just so so oil, your gonna need to rering the sled more often, the snowmobiles of today are leaps and bounds above in power output what they were in 1978, and so should the oil protection you use. You cant beat technology, 100 percent man made synthetic oils out do petroleum based oils 10 to 1 no question about it. If you take apart a engine that has run yamalube its whole life you will find a dry, baked appearance on all internal parts, lets take apart a engine run with amsoil or another quality oil and youll find a nice sticky oil coating and almost no signs of wear.

In closing, a compression test is a tool, but you need to use the right tool to complete a job. If you want to know the condition of the rings, a leak down test is the tool to use. If you have over 3000 miles and you have run so so oil, you most likely need to freshen up the engine, even though it still starts up fine and runs good. There is lost performance waiting to repay you for your efforts.
 
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Now thats a good informative answer. That needs to be moved to the tech section. I am going to copy it and email it to myself, just incase it is lost in the server work. Maxdlx
 
i did a compression check cold pto-110 mag 122 center 125.What do you need to do a leak down test?Would like too make sure everything is in good standing.
 
I replace my rings at 3000 miles!!!!! Thats not to say you should!!!!!! I use synthetic KLOTZ and I usually don't keep a sled past 5000 miles,,,, but,,,when I take them apart at 3000 miles, i don't even have to scratch up (hone) the bores!!!!! They run just fine!!!!! Gary Oles nosboy
 
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