I have a 85 IROC Z28 that I recently picked up. The motor and car have a documented 22K original miles.

When I park the car in the driveway I get a drop of oil under it most of the time from the back of the motor where it is leaking and causing the tranny and all to be wet. I was reading somewhere in the FAQ's that the 85 305's had a 2 peice rear main seal and that GM updated this in the later years to a one piece seal. I also believe I read something about a conversion kit to turn the 2pc to a 1pc.

Would anyone have information, a link or part numbers that they would recommend for the conversion if possible? Or are there any tricks to getting the 2pc rear main to seal properly when I go to replace it?

2nd... On the passenger side of the intake in the middle I have a small amount of oil leaking onto the outside of the intake. I spoke with a friend of mine and he said that oil tends to come out of the bolt/heads on these engines and that I should just pull the bolts and use silcon or a rubber o-ring under the heads of the bolts to seal them and this would get rid of the problem... Not so sure about this and was wondering if anyone had idea as to the source of the leak and how I could stop it.

Other than that the car runs awesome... and the 2 leaks are very minor, regardless though I would like to fix them and not see the oil or perhaps keep the problem from getting worse.

Any recommendations and information would be much appreciated!

Also a link or source where I could get a GM Helms/Shop manual for a decent price on the car would be excellent... : )

Thanks,

Rob Schwartz
02 Pewter WS6, Lots of Bolt Ons
85 IROC Z28, 22K miles, K&N Filter, Hypertech Chip, Low Temp Stat, Shift Kit.

 

Congrats on a good find in that car.
The rear main seal is indeed a 2 piece and they do make an adaptor to use a 1 piece seal at the rear main, Summit has/had them.

From the factory the 2 piece seal mating ends are parallel to the oil pan/block mateing line. When replacing the seal it is reccomended that you rotate the whole thing 90 deg so it doesn't line up like factory, and use a little silicon on the ends where they meet to help seal them up.

Your friend is right about the bolts wicking oil up onto the intake manifold, however, don't use silicon to seal the bolts. Instead use Permatex PST thread sealer, this is the best thing for those pesky leaking bolts

 

Morley,

I appreciate the awesome response! I was thinking about something and I'm not sure if I'm right...

The 1 piece rear main seal is a better design from what I understand, but if I remember correctly you have to have a crankshaft that accepts the 1 piece rear main seal. Is this correct? I don't think I can change it to a 1 piece without changing the crank.

On the bolts, should I comletely remove the bolts and coat the threads or just back them off and run a small bead under bolt head?

Thanks again! I appreciate it.

 

Correct, you do need a crank for the 1 piece seal.
You'd need to remove the the bolts completely and clean them with something like acetone or brake parts cleaner and clean the holes too, to remove any oil and ensure a good seal. If you aren't removing the intake, just do the bolts 1 at a time. Also the 4 end bolts don't need to be done since they aren't open at the bottom.

 

Morley,

Again, more excellent information! I appreciate the info on the end bolts, I suppose I will loosen them up though and then re-torque the entire intake back down to spec in the correct order after pulling the center bolts, cleaning the threads and chasing the threads in the heads. This should fix my problem completely.

Over the years I have not had much luck in owning 7 different f-bodys and getting the rear mail seal oil leak fixed... They usually seal for awhile and eventually seep again... arrgg... That is one nice thing about the LS1 motor in my 02, oil pan looks like a trans pan and it doesn't leak... : )

Again, appreciate the quick response and super information.

Rob

 

About the rear seal thing... the adaptors you see are for putting a 2 piece rear main seal crank into a one piece rear main seal block. You absolutely cannot put a one piece rear main seal or crank into a 2 piece rear main seal block. Its impossible. Dont even think about attempting it.

As for the leak, first I would try tightening up the oil pan bolts. Sometimes, they back off. Sometimes, they are even missing. Also, replace the PCV valve. It may be stuck, and that will cause leaks.