I have been working on SBC's for a lot of years. I have installed lot of main seals, but have never tried it with the motor in the car. I rebuilt my 350 over the winter. It runs great but I have a very small leak at the rear main seal. I did all the tricks while installing the seal. A little oil on the seal. A dab of silicone on the ends of the seal. Offset the seal from the parting line. And put a dab of silicone at the corners of the main cap. And yes it is facing the right direction. Still leaks. It seems that I would want to remove the rear main cap and loosen the other mains a little bit to maybe get a slight amount of wiggle room at the seal area. But then I don't think that the crank would come down any while hooked to the TC and trans. Or will I be able to turn the seal in? I kinda hate to do it this way, and if the engine really should be pulled to fix it, I think I will just live with it unless it gets worse. It's very, very slight. It just pisses me off. I haven't had a rear seal leak on any of my motors for a long time. Is this an advisable operation? What are the chances for success (or failure)? What experiences have you guys had?
you don't need to loosen the mains. I never put sealer on the seal itself, only between the cap and block, in a line between the seal and the pan gasket. Offset helps. But it's an SBC with a two piece seal, and sometimes they do leak a bit. I did have some luck with a seal with an offset lip, on one engine...it moves the sealing area away from the groove that's worn in the crank.
I have changed several of them that way successfully. I just removed the rear main cap, and spun them in. It’s not that hard. Was the block aline bored? That can lead to some rear main leaks. Sometimes you have to add a shim under the lower half of the rear main seal, because you have moved the crankshaft up higher than it was.
Didn't have it line honed. I did have the crank polished. That just made me think. I used a +.001 half shell and a standard half shell bearing to tighten up the rear main clearance by .0005". I put the +.oo1 shell in the main cap. My thinking was to keep the crank in the same relationship to the block. I wonder if that is causing the leak. It's small. I mean I might get a drop every 2-3 days. But it still pisses me off. At least enough that I would pull the pan to fix it, but not the whole motor.
Like Jim said,,,it’s probably just the seal . Yes,,,,it’s very easy to replace,,,,,well somewhat easy,,,LoL. I really don’t think the .001 shell has anything to do with it . Seal it like Jim said,,,,,and you should be good to go . Also,,,,,before you tear it down,,,,,,make absolutely certain it is the main seal that is leaking . It wouldn’t be the first time someone has mistakenly blamed the rear main . Good luck . Tommy
Welcome to "GM rear main seal annoying leak club". If you keep thinking about changing it long enough, it will then be time for rings & bearings, and you can put a new one in. So it can start leaking a few thousand miles later. Repeat as necessary.
It’s up to you, but I agree with Jim. I’ve owned quite a few small block Chevys, and I’ve yet to have one with zero oil leaks.
I've done a few in car. After you get the upper seal out, I always spray some carb/brakleen on a few pipe cleaners and run them through the seal groove in the block. In one side, out the other a cpl times, to get any old oil/crap out of the seal groove. Rubber tip blowgun to dry. Oil the new seal, and work it into the block. Jim's suggestion on the silicone is perfect.
The old equation I'm always dealing with...frustration that all my old junk leaks vs. the cost and time of repairing it AND weighing the likelihood that it won't start leaking again two years down the road (or less). Generally, if it leaves a mark bigger than a coin when I park it, it's time to deal with it. That's not a hard and fast rule either. To stay on topic, if you change the seal in the car, be careful to not peel the backside of the new seal as you work it around the crank. It probably doesn't matter much if you do, but it's something to look out for anyway. I'd leave it, personally.
that's what the little piece of plastic with the tab is for...lay it into the opening to cover the sharp parting line on the block
I had this problem on an off topic sbc equipped truck, fresh rebuild, took all the precautions as you did...still had a very minor and annoying leak. I couldn't justify tearing into it for a couple drops but it bugged me. I was discussing the leak with a friend that owned a transmission shop that owed me a favour. He said that he'd pull the tranny and fix the leak for me to return the favour..sold. When he took it apart, he noticed that when I painted the engine after the build, I had not bothered to mask off the rear of the engine. The crank hub near the sealing surface had paint and overspray that did not stick well (it would have been oily from assembling the engine), and parts of the paint/overspray were flaking off near (or at) the sealing surface. He figured that was the cause of the leak. He cleaned up the hub, replaced the seal and it never leaked a drop after that.
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