So I bought a LS1 (99) which I'm going to be using in a swap.
When I pulled the plugs I noticed that the plug from cylinder 8 had some oil on it.
Compression test shows that cylinder 8 had reeeally low compression.
I'm assuming piston rings gone bad?
Any other suggestions on what it could be?

I haven't done a leakdown test (is it nessary?) or taken anything apart yet so wanted to get some opinions before I did anything.

So if it's the piston rings, would it be possible to just replace those? Or would honing the cylinder walls be nessesary?

Thanks for the help everyone!

 

sounds like rings to me! How was it running when u bought it?Strong? It would not be very smart if you didnt hone the walls after replacing rings...ya know?...Might aswell.

 

I have oil residue on my plugs almost everytime, i think my valve seals might be going bad...

 

one more for the rings....i just had a 99 motor before i got my 01....MAKE SURE YOU CHANGE THE OIL PUMP, also check the bearings....just a lil advice

 

Could also be vent valves as well.. Pull the heads or do a leak down to get an accurate diagnosis

 

What are your compression numbers? Does it smoke at WOT, when you FIRST start it in the morning, when?

VERY CURIOUS what all 8 cylinders came in at compression wise, please post the #'s

 

Thanks for the replies.

Unfortunately I have no idea how the engine runs as it's out of the car and on an engine stand right now.

I will post the compression test numbers when I get home. Unfortunately I'm on the road right now and don't have that in front of me.

 

my v6 engines numbers went down from the 170-185psi range to 75-85psi range.
I put oil in the cylinders and did a compression check and the pressure immediately shot up to 160psi range. So I knew it was bad rings.
Should've done a leak down test...
You always have to rehone the cylinder walls when new rings are put on.
And You always have to use new rings when the pistons are taken out.

 

how do rings go bad?...i have never really thought about it..

 

mine occured from overheating , being very lean 18.0:1 +++ AFRs, extra pressure.

 

black7, you cant just do a compression test and ASSume the rings are bad.
You should put oil in the cylinder you do the compression check on, if the pressure immediately shoots up (on the first crank) then its definately bad rings.