C3smallblock

My mechanic friend has told me that the leak in my rear main seal on my 350 engine is a major job to repair. It is only a small leak, but he said that to replace it would be a huge job and not worth the effort. He said that this leak is typical of the 350 and that even after replacing the seal it could start to leak again. He said that if I wanted to get it done I would be best to take the car to someone who specializes in this type of engine/work.

I was wanting to get it fixed to try and get rid of the almost constant smell of hot oil on the bottom of the engine.

Do they often leak, and is it worth fixing?

Cheers
Kev

Corvettetodd

If your 1976 Block is the same as my 71 Coupe (2 piece rear main seal) it is not a major repair.. Again I am not sure about the 1976 model (maybe need to drop the exhaust crossover pipe), but on my 71 I dropped the idler arm, loosened the oil pan bolts and removed the oil pan, and replaced the rear main seal..It took me about 4 hours, but most of this time was cleaning all of the old gasket adhesive from the pan and the block. I used the one piece blue Permaseal pan gasket and so far, no leaks. I cant imagine it taking a shop more than 3 hours to change the seal..
On my 68 Camaro it was a huge pain because the engine needed to be lifted to clear the front crossmember.. The Corvette was a piece of cake in comparison..

gerry72

This is not a major repair. Well, it may be for your friend, but that would be a different story. I did a quick Google to save time in presenting what is abundantly available: http://www.corvettehacks.com/article5.html

This assumes your friend's diagnosis is correct, though. It could be a leak in the intake valley seal, the valve covers, or just an oil pan gasket. If you do this as a fix to the rear main seal and you do it correctly, you would solve your problem if the leak was in either the main seal or a pan gasket. If the leak is in the intake gasket or valve cover, you will have accomplished nothing other than gaining first-hand experience in repairing components that weren't broken.

Golden

In fairness to your mechanic he may not be aware the seal comes in two halves, can be done in situ and thinks like most rear mains that the 'box needs to come out.

wcsinx

If you smell burning oil, then I doubt the rear main seal is the only thing leaking. The pan & main seal area doesn't get particularly hot. Smelling oil burning would indicate a leak higher up like the valve covers or intake.

cart3113

Before you tear into it. Check the oil pan bolts. I thought I had a main seal leak and checked the bolts. I couldn't believe how loose some of them were especially the ones at the back of the pan. I tightened them up and no more leak.

billla

I'd do some careful detective work for sure before looking at the rear main seal.

I'd have to agree that while it's not a particularly tough job, it isn't trivial to do in the car.

pwcheenie

On my 80, the pan gasket was the biggest oil leak. Took off the steering linkage to drop the pan down. Replaced the rear main seal, 2 piece, then installed new one piece pan gasket. Reattached steering linkage. Some mechanical experience is helpfull. I am not a auto mechanic by trade.

vettehardt

The 76 motor is the same as the 71 with a 2 piece seal. The oil could be dripping off of the motor and getting on the exhaust is why he is getting a burnt oil smell. I have the same problem with my tranny fluid. It keeps leaking on the exhaust and burnig. I have replaced the rear seal and pan gasket, but it hasn't fixed the problem. I am going to be looking in to it more this spring.

As others have said, drop the idler arm and oil pan. Use a punch to gently tap the top half of the seal around until you can grab it with a pair of pliers. Pull it out the rest of the way. Insert the new seal, put some silicone on the corners. Then replace the oil pan with a new gasket, and hook up the idler arm. You are good to go.

jhopper408

Would the rear main seal be the same on a 77. I have some sort of leak at the bottom of the rear main seal. But I do see some oil on the valve covers. I have a guy working on it right now. But he's not sure if the oil is coming from the rear main or the pan gasket. He's a great mechanic. But will he be able to figure it out without trouble shooting? The engine only has 800 miles on it. Any thoughts would be helpful. ItdI a 383S
.
Thanks
John
John.

TimAT

Your 383 could be either type seal- it just depends on what your builder used for a block.

jhopper408

That's exactly what the mechanic told me. He knows what he's doing. Thanks so much.
John

Bills17n72

the rear main seal is not that big of a job ,someone might be pulling your leg!!!

jhopper408

Well the mechanic didn't seem to think so either. There farm equipment guys. No problem
thanks
John

mark79,80

Felpro makes a double offset rear main seal. I would use this one as it moves the sealing area to a new section of the crankshaft. It is very easy to tear the upper portion of the seal, as you slide it around the crankshaft, even using the provided shoe horn. I normally purchase a spare, just in case.
The felpro one piece oil pan gasket will also insure a leak free job over the original four piece design.

berlinlake

How do you walk the crank back and forth to set the thrust clearance? I may have to replace my seal and it's been years since I've done anything like this. Debating whether I want to tackle it or just pay for it. It might be a good project for me but want to make sure I can do it. I think I understand everything I've read above but the crank comment is new to me. I don't see it mentioned on the Corvette Hacks article. My car is a 64 so maybe it's not exactly the same.

Sayfoo

Scotty Kilmer says this stuff actually works/

Mark G

All good advice. I agree with the others; clean everything off THOROUGHLY with carb cleaner and/or engine degreaser and ensure there aren't leaks up top. You gotta get things clean and dry first. You could use a dye in your oil too to help pinpoint the exact point of the leak/s. Then run it a little. You almost need to get a small inspection mirror in the back by the firewall to see the rear intake seal, or the distributor seal (if it's leaking). I can't remember if there is an oil galley plug back there too (unlikely but you never know). Would not be uncommon to have a rear intake leak and esp valve cover leaks.

Valve covers on 350s leak frequently. The initial design I read was to make the raised cast portion on the head where the valve covers mate to taller, but due to cost they reduced the height ...which led to millions of chronic valve cover oil leaks for many years. Like the guys have said, a lot of other common oil leaks on SBC's can and usually do spoof a rear main leak.

If it ultimately turns out to be the rear main, I've done the job more than once. Not a joy doing it laying under the car, but I've done worse jobs. Doesn't require a lot of special skills or tools, just step by step. They make a special inexpensive tool to push out the top portion of the seal. Mine never leaked afterwards.

7t9l82

Do you guys know how old this thread is?

berlinlake

I've been reading my shop manuals and I'm starting to feel it's not that difficult. The only question I still have is the statement about walking the crank. What exactly does that mean? I'm not seeing in the manual where you do anything to the crank other than removing and replacing the rear main cap.