Frt and rear sbc main seals both leak

OK, I have searched, and searched, to no avail. I've got a brand new rebuilt sbc 350 with one piece rear oil seal. Started her up and broke in the cam, set lifters, adjusted carb, ran it on and off all day, NO LEAKS. On day two I ran it up and down the street a few times, nice and easy, 25 - 30 miles an hour, brought it back in the barn and looked under to find several drops of oil at both the front and rear of the oil pan. I had a breather in each valve cover, but they were used, so I threw a couple of brand new ones on. Another short ride, again same leaks. I decided to try a PCV on the right side, left the breather on the on the left. Still have the leak. The guy who did the re-build is close friend and he has been building motors for more than than 30 years, he uses only good gaskets. This is a fairly mild engine with some head work, flat top pistons, and hydraulic cam. The one thing that has me wondering is the oil pump. High pressure, high volume about 45 psi at an idle. I don't believe the big pump and high pressure are needed, but could it be causing my trouble? Thanks in advance, Bill




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A damn shame, nice truck. I have lots of different ideas but they are all guesses. I can say it don't have nothing to do with oil pump pressure or volumne.
I want to say it has something to do with pressure and lack of pcv. It might be the machinest got interrupted while putting the pan on oit and didn't get the gasket sealant on it proper.
You'll just have to bite the bullett and pull it out for a proper looksee.

 

Bill, I would lean toward the pan not sealing at the corners, than both front and rear main seal leaking. If the corners of the pan weap, the oil will follow the curvature of the rear and front mains until it drops off the lip appearing like it came from the seal. Did he use a 1 piece pan gasket? Did you replace the pan, possibly a cheap imported pan not fitting correctly, very common these days.

 

No, or inop PCV valve.

 

I have had more than one rear seal leak turn out to be either distributor or oil pressure switch leaking and running down. Check top of engine in that area good for leaks also had the bolt in front of block near fuel pump missing and leaking.
wrenchn

 

I have seen the chrome timing covers leak where the bottom lip is spot welded on. Could have a groove worn into balancer sealing surface. The rear seal leak could be the pan. Even the best builders can have a bad day and mess up a seal install. Clean it all off real well, put some tracer die in it and see if you can tell what the leak paths are. That will tell you if it is the seals or, the pan leaking. There is no pressurized oil at the front seal just the oil running down the front of the block to lubricate the chain. Just use good quality seals if you replace them and be sure there is no damage to the sealing surface of the crankshaft and balancer.

 

Aside from what has already been said you may want to take a look and see if the pan bolts are snug. I have a long mile SBC (with a stock pan) that I had to snug the bolts 3 or 4 times before they stayed, they seem to want to loosen up on some engines for some reason. I always thought that it was a gasket quality issue, but who really knows.

 

Thanks guys for the ideas, that is just what I was lookin for. I'm retired but I took on a part time job at a local archery store for another good friend. He is gone out west on a mule deer hunt and bow season opens in Michigan in a little over 3 weeks, so I nead to get over there. As time permits I'll follow throgu with a few of those ideas.

Thanks again, Bill

 

drive over and visit your buddy who built the engine, he might have some ideas about how to fix it. And hopefully he wants it to work right...

 

I'm in no way trying to hijack this thread, but it could help in the end. Could someone who has used a so-called "speedy-sleeve" to help with a sealing issue when a crank snout has worn give us the good, bad or indifferent about their use. Thanks. Hope the OP solves his leaks. Maybe the builder didn't tighten the pan bolts completely and after a couple heat cycles they need to be snugged up. Just sayin'. good advice above also to check for oil pressure sender and good seal at back of intake.

 

speedy sleeves are difficult to install straight....but if you can do it, they work ok. Usually a damper with a worn seal surface has worn out rubber in it and needs to be replaced anyways.

 

....Thanks for that advice, Squirrel. Your knowledge is always appreciated......Don.

 

Maybe The seals Or gaskets where blew out from crankcase pressure in the initial start up before you changed the breathers & installed the PCV? And Ive had a crome front cover that always leaked. It seems that quality was poor and the front seal wasnt properly lined up (centered) with the crankshaft. oil leaks can be at a entirely different than where they are dripping. You can pressurize the crankcase with compressed air and find oil leaks without the engine running. I once worked on a v6 GMC that was a machine shop rebuilt long block. It poured oil from the front & rear mains. I Changed the seals and it still poured. Several folks had worked on it before me. . I finally figured it out. I pulled the engine out and set up a dial indicator up on the rear seal part of the crank. it went up and down about .020 out of concentric. The crankshaft had been turned and was off center. The owner & I hauled it back to the rebuilder. they immediately saw the problem. and exchanged the engine and paid for the labor.

 

My O/T Vette exhibited the same symptoms. It was the oil pan gasket. The PO overtorqued the pan bolts and ruined the pan gasket. Don't overtorque those bolts.

 

Squirrel is correct as usual. That said I got about 140K on a sleave, no problems, I got the damper cheap because it was worn on the sealing surface. Who knows why?

 

because the engine ran warm and the seal got hard and ate a groove in it?

 

Could be I suppose. It was chewed just enough that it wasn't going to seal and the sleeve didn't cost much.

 

Isn't there 2 different sizes for a front oil pan seal for a SBC? I remember ther being 2 rubber gaskets in the oli pan gasket kit for a SBC. Maybe they used the wrong one. I changed to an aluminum pan once and used the wrong gasket and it leaked.

 

The timing cover changed in 1974, they went to a thicker gasket between the cover and pan

 

after I put the pan on I run a bead of silicone around the front and rear of the pan in the rubber gasket area and wipe off the excess to prevent this, works for me

 

I finally got away from that store long enough to take the pan back off my motor. All the parts are GM, no chrome and no China, and seem to be in really good condition, the pan is straight and and so is the timing chain cover, at least what I can see of it. There is a one piece oil pan gasket on it, but not blue, it is grey. Has any one ever seen a Fel-Pro one piece gasket that color? My friend says that his machinist always gets the re-build kit and he was surprised to hear it was not blue. I haven't been able to find any name on it, but USA is embossed on there. The front and rear corners were doped up with silicone and everything looked like there was no way it could ever leak, but I saw it with my own eyes.

 

I have replaced a rear main several times, only to find the culprit to be a cam plug not properly seated. They make a tracer dye for engine oil to help you trace it down.