Viper Top End Clearances

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PrecisionEngine

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Hi everyone, I hope everyone enjoyed the holidays.

I need a bit of advice. I have a 2002 viper with ~6000 miles. It's never had topend work, so I decided to take a look. I disassembled the PTO cylinder and all the Clearances are within spec with exception of the piston skirt. Piston skirt measures 2.7095". Should I bother changing them?

Thanks and Happy New Year.

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I dont have my manuals with me what was stock spec on skirts? Odd everything else spec'd out ok, Looks like the piston is brand new. Depending on what you want to do and how far you want to go into it i would run them, put New rings on and clean everything really well. If your going to spend the money on new pistons i would go all the way. Tear bottom down, new crank seals ect.
 
super1c said:
I dont have my manuals with me what was stock spec on skirts? Odd everything else spec'd out ok, Looks like the piston is brand new. Depending on what you want to do and how far you want to go into it i would run them, put New rings on and clean everything really well. If your going to spend the money on new pistons i would go all the way. Tear bottom down, new crank seals ect.
Click to expand...
Book says 2.7137 - 2.7138. I can't even find a bad ring or gap. The only thing I noticed is a bit of pitting in the top ring land.

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What is important is piston to cylinder clearance. You should measure this at the bottom of the cylinder (intake side to exhaust ) and piston skirt (intake side to exhaust). Book says 0.0028 to 0.003, + 0.10 wear limit.
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I have a feeling you'll be within limits at the skirt. If so, I would reuse the pistons with new rings. Like Super1c said, if you go to new pistons, I would go thru the bottom end as well.
 
as mentioned check your skirt to wall clearance and see if you make the limit. I have before used swain tech coating on the pistons to bring them into the clearance, you can get it up to .004" thick applied and it works great, makes the piston more slippery as well. That's the key with these engines keep the rings fresh in them and the pistons last a long, long time as they are powder forged units. Its when the rings are never changed that the piston then begins to walk/rock in the bore and wears the skirts, eventually leading to engine failure when the skirt breaks off and ruin engines bottomend. Usually comes down to what kind of oil was used and how well the sled is maintained, I have seen engines with 8000-9000 still be in spec and seen some with 4000 be worn and need attention.
 
Thanks guys. Your wealth of knowledge is amazing. I decided to take a peek because my compression tester was showing 75psi on first two cylinders and 72psi on the PTO cylinder.

I know The gauge is good but it has a long hose. I wonder if it's just the hose expanding.

Last night, after looking over all the rings and noticing only some pitting on the bottom land, I decided to reassemble. I'm going to run it a bit longer.

Maybe next season I'll get ahold of some one and have it ported and change a few things.



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