What does it mean when one cylinder plug has oil on it? All other 7 were cleanly burned. I did a compression test and all cylinders tested around 150 psi.

 

Doesn't look like oil, looks more like richness. Leaky injector or the like.

 

If it runs okay I'd probably just put new plugs in it and try to forget about it

 

If its oil, the rubber Valve Stem Seals on #7 may be worn and leaking a little oil into cylinder.

Had similar issue on #5 on an LS1 and it was Valve Stem Seals. Shop replaced the seals when doing valve springs and that fixed the issue and leak.

 

I agree that's what it is and that's why I said it was okay to keep running it, I would keep running it until I got excited enough to modify it, require getting into it and so Id change the seals while it was there, which there are other posts on here about valve stem seals another poster Right now has black smoke at the big end of the track like I did. Valve stem seals are cheap but you have to remove the valve spring to replace them.

 

I think its a valve seal issue i swapped the plug over just that one and the other clean cylinder cleaned that plug right up. It is just that 3rd cylinder back on the drivers side the other 7 were clean. As far as compression i had tested it in the morning with alot of condensation and got the same 150 psi on all 8 cylinders. I did put oil into one cylinder to test for rings and still came out with 150 psi. As far as putting too much oil for a ring test that im not sure of. However the same day or later in the afternoon before returning the compression tool to autozone before 7:45pm they closed early christmas eve i tried two other cylinders real quick with fuel/ign disabled and just the two plugs removed and they came out at 165 psi 162 psi. Not sure what changed but maybe going to perform a leak down test but would have to purchase the tool as they dont have them for the rental tool at any of the local parts stores. Someone elses ls1 cam with the same compression tool tested 180 psi on all 8 cylinders. Not sure why mines a bit different but was happy to see a raise in compression before returning the tool. They are new 4$ each bosch platinum pre-gapped that i changed after doing headers and all new fresh fluids engine oil, trans fluid with filter and valvoline diff fluid. It does need new spark plug wires the car runs great otherwise but they did get damaged when performing the compression test the top white plastic pieces on the coil plug fell apart.

Im gathering parts for a cam swap as the balancer needs to be changed and wanted to make sure the shortblock was in ok shape before putting a cam in a daily driver corvette. Already have the replacement balancer and cam waiting to order some pac-1219 spring set and comp 528-kit valve seals. I may do the leakdown test before to test the rings and possibly change the head set with fel-pro permatorque gaskets and different set of 241 or 799 heads in better condition. Is there anyway to find out if the miles can be swapped on a rebuilt title 99 corvette? It was wrecked upfront by the previous owner and has 92k miles according to the cluster but not sure if he could have swapped engines or changed cluster and/or ecm to read a different mileage. Does anyone know where the miles are stored? It is a 99 corvette with 853 head set and the ls1 corvette intake with no egr so its hard to say if they had swapped engines as it may have gotten damaged in a collision. The rear diff is still a 3.15 gear per factory glove box sticker with jet black interior option codes.