Hello fellow Vette owners,

I have a major problem with my C5 that has been in the shop of one of the forum partners, I will not name who at this time. Long story short, I brought the car in for a tranny rebuild (synchros for 3/4 and R gears were bad) and an engine issue that started on my way home one night the car lost oil pressure down to about 10PSI and I could hear audible valve train clatter. I had the car towed to the shop for diagnosis and repair after reading positive reviews and recommendation by a friend who had brought his vette there.

First a little bit about my car, it’s a 1997 C5 coupe 6sp 136,000 miles, has a standard LS1 lower end, with AFR 205 heads which have been milled, cam (don’t know the size it was installed when I bought the car but likely SLP with .590” lift, the car has SLP badges) FAST 102mm intake manifold, MSD coils, MSD wires, Corvette Mass Air Flow Sensor Granatelli Motorsports, LS2 90mm throttle body. The car also has the Billy Boat exhaust system on it with an X-pipe and long tube headers. During his work on the car the mechanic also informed me that the car used to be supercharged due to the timing chain being pinned and other things consistent with a supercharger kit that was removed before I bought the car. I bought the car from a stealership not a private owner (my mistake) who was not even aware that all of these parts were on the car.

The mechanic determined that the car was throwing a code for a misfire on cylinder 5 and proceeded to tear down the engine to find the cause. It was later found that the water pump was failing as well as the oil pump; one lifter had collapsed with a broken rocker arm. It was also found that a valve train bearing had spun. The engine was pulled and sent to a machine shop to repair the bearing issue. The lifters were all replaced as well as the bad rocker, seals etc and the cylinder head from cyl 5 that was damaged. The only internals not replaced were the crank and pistons and the other cyl heads. The block was pressure checked at the machinist before returning to the mechanic and passed. The block was reassembled and installed in my car. It fired however with the EXACT SAME valve train sound and no oil pressure.
I am trying to give the mechanic the benefit of the doubt here but he is saying he has not seen this issue before after a rebuild. Some things that have been tried so far are; oil flow check in the rear oil galley – Oil is flowing but pressure is not being sustained to the lifters, seals on the rear of the engine were checked and are correct, the engine was pulled again and the machined parts and the cam were sent back to the machinist to recheck the bearing journals and were deemed correct, cam bearings were correct size and placement. The engine was reassembled on a stand to attempt to fire outside of the car. I haven’t heard back whether this was successful or not but I am at my wits end with this, it has been over 4 months and I still do not have my car fixed after several thousand dollars spent.

I am sure some will say I should have just bought a new LS motor, however it was presented as a simple issue to fix by the mechanic and slowly more and more things were found and by that point I could not afford to shell out more for a new engine. I am looking for anyone with a wealth of LS engine knowledge that might have a clue of the direction to take to fix this since it appears that the mechanic can’t do it.

Thanks in advance,

 

And what would you like us to do?

 

There can be an issue with oil pressure if you screw up the placement or pinch the o-ring between the oil pick up and the oil pump? I thought that led to no oil pressure though but it can't hurt to check.

Any possibility of a clogged filter?

 

@chaase I can pose that question to the mechanic, he says oil is flowing but not pressurizing the lifters, checked the pre load and let it run for 3 minutes and still no pressure. The block was disassembled and bearing journals were checked and verified correct as were cam bearings. The filter was changed as was the oil pump and the seals and gaskets. The pushrods were changed, the ones that were in it were 7.35 and changed to stock 7.4 which is the only real difference between the previous setup to the rebuild.

@3boystoys I'm looking for advice on what to check/cause since it seems like there is no end to this issue, appreciate any input.

 

Well, I would check the oil pump. You could get a pressure tank and try to get pressure in the system to see if it can hold it. The "O-ring" on the pump is a know issue if your not carfull on installation of the pump, it can twist/pinch and leak.

 

Were the barbells re-installed? That will cause this even with a good pump and is a common error for those not familiar with the LS motor.

Was the cam plate seal OK when removed/re-installed?

The list can go on but this should get you started. Sounds to me like an assembly error.

Also, did they work the heads and what rockers are being used? AFR heads have a multi-angle valve seat that should be worked by AFR or someone who really knows these heads. You might want to PM Tony Mamo if there are issues with the heads themselves.

 

I think the rear cam bearing not pressed in far enough can cause low pressure too.

 

@vettenuts 3boystoys Yes, Barbells were reinstalled and checked, oil pump O-Ring were checked and no issues with that as the pump and pick up tube are moving oil volume to the lifters but not giving pressure. The front cam plate seal is good and not leaking, but not able to see the rear seal. I don’t believe there was any issue with the heads, I am not sure about which rockers are on it but the one that was broken was replaced, thanks I will ping Tony as well for the heads.

It’s hard for me to know what questions to ask on this as I admit this is over my technical knowledge on engines, thanks for the suggestions so far guys

 

To me the only things that would cause the problem you describe would be a faulty oil pump or a leak in a seal. You may end up having to take this engine to another mechanic to find the problem since the one you used to do the work cant seem to find it. It sucks especially with the amount of money you have put into it...I would ask the Mech that has done the work to reimburse me some of the labor since he cant fix it and then take it to another mech that may have more exp or aptitude when it comes to LS1's

 

Hereis the oil flow circuit for LS engines:

 

Quick update: The block was partially assembled outside of the car without the valvetrain on with a manual pressure gauge and it is building pressure. Will find out if it is the valvetrain causing the lifters to collapse or leak oil soon with the assembly completed. That will at least narrow down the possibilities.

 

46 years ago my brother built a 327. He had a similar problem. The motor ran good because it had solid lifters but could not get the oil pressure past 10 psi or so. After much diagnosis finally we found out that the cam was the wrong application for that motor. I would say replace the cam and cam bearings.

Good luck