Rebuilt 1970 4 bolt main motor rear main seal leak.

Discussion in 'Tips 'n' Tricks Topic' started by jsksystem, May 16, 2020.

  1. jsksystem

    jsksystem New Member

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    The original motor (350) in my 79 Z28 was worn out so I bought a rebuilt 350 that had been sitting for 2 years (never run since it was rebuilt). The owner says he'd place oil in the spark plug holes and turn the crank every month since rebuild. I had it installed and it fired right up and runs great. The mechanic says it's leaking 1 drop of oil every 15 seconds from rear main seal where the chrome oil pan connects. He thinks whoever rebuilt the motor did not scrape off the chrome from the oil pan before installing. Or he says if they did, it should have dried out from sitting for 2 years. Any ideas or thoughts about what I can do here besides replacing the seal? Is there any chance som kind of stop leak could help? Thanks.
     
  2. jsksystem

    jsksystem New Member

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    UPDATE: I checked the oil and it's 2" past the full mark. I just drained 7 1/2 quarts of oil without removing the shorty filter so I figure there must have been 8 quarts of oil in a 5 quart pan. I changed the oil, ran it for 10 miles, got under it and guess what? No more oil leak.
     
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  3. jsksystem

    jsksystem New Member

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    I hope I did not damage the motor by running it over 30 miles with all that oil.
     
  4. badazz81z28

    badazz81z28 Veteran Member

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    Aint much you can do about it now....I guess years of dumping oil in the spark plugs added up. I know this is just poking you in the eye, but you didn't drain all the old oil and re-filled it before you did the first fire up?
     
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  5. jsksystem

    jsksystem New Member

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    I had a shop in town swap the motors. I told the mechanic there was oil in the system but apparently he must not have drained it before adding the 5 quarts. I will talk to them on Monday. So far, it seems no harm was done. The engine runs fantastic and the rear main seal oil leak has stopped.
     
  6. Twisted_Metal

    Twisted_Metal Administrator Staff Member Lifetime Gold Member

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    Extra oil shouldn’t have hurt anything.
    The crankshaft may have been splashing in the oil but that would just be more of a horsepower loss than causing any damage.

    I think it will be fine.

    The very high oil level could very well have been the cause of the leak.
    (Changing the rear seal is quite a bit of work.)
     
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  7. badazz81z28

    badazz81z28 Veteran Member

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    True story....years ago I bought a 350 that was rebuilt, put it in my car and leaked like a SOB in the rear main seal. I ran it like that for a while thinking I had a bad seal and I would get around to it. One time while I was drag racing it, I ran it so low the OP light turned on. I ended up pulling the engine back out to swap the seal and you never guessed there was only 1 of the two pieces there. The main cap had a seal, but the block side did not! You can never trust, gotta double check!
     
  8. KingofThings

    KingofThings Member

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    Scrape the chrome off the oil pan??? What?
    First off, why?
    Second, if it flakes, and I doubt it wouldn’t, there will surely be some getting into the oil and that stuff is like razor blades and will slice you up.
    I’d sure like to know what this is about because I’m having trouble with one-piece pan gaskets. :p
     
  9. Robert stuart Bell

    Robert stuart Bell Rsb78LT

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    Silicone doesn't like sealing against chrome so if you scrape the chrome off it seals better but then you have chrome flakes in your oil, why I don't use chrome engine parts. Looking good and working good are completely separate things.
    Have any of you tried putting silicone between the pan and the seal? I had issues with my small block leaking at the bottom of the aluminum timing cover and the rear main, I replaced the pan gasket and put silicone on both sides of the pan gasket at the front and back hoping this solves my problem but I haven't gotten my car back together yet
     
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  10. KingofThings

    KingofThings Member

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    If you’re using a one piece pan gasket you’re not supposed to put anything on it except in the corners as they state.
    Anything else will void the warranty.
     

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