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Thread: Rear Main Seal

  1. #1

    Default Rear Main Seal

    Can the rear main be replaced without pulling the engine? The '34 manual doesn't tell much as it assumes you are rebuilding the engine and it is out of the truck. Some mechanic friends tell me there is a tool to pull the old seals out but reading the '34 it mentions 'cement' which tells me the seals are glued in there.

    I am NOT a mechanic but in the old days I have rebuilt engines out of necessity, (no money and I had to get to school!) so not afraid of trying anything.

    I do leak oil from there but not serious. Maybe better to let it alone?

  2. #2
    Join Date
    Sep 1998
    Location
    North Central Wisconsin
    Posts
    11,520

    Default

    I changed mine in the truck.

    The only thing cemented should be the oil pan seal which is on the outside of the filler block, not on the inside where the rear main seal is...it is a seperate rubber piece

    Pull the pan and you can pull the filler block at the rear that has the lower half of the seal in it.

    The upper half may move when pushed from one end or it may not. If it doesnt want to, you need to get something softer than the crank...a brass drift works...a nice piece of wood works too...drive one end of the seal so the other ends sticks out and you can remove it. Make sure you clean the seal groove out as best as you can.

    To install the upper part, take a piece of good string and guide it up and over the crankshaft through the upper seals groove...tieing it to a long bundle tie or a couple of twist ties hooked together will get you there...then tie a slip knot near one end of the upper half of the seal. pull the string from the other side of the crank from the seal and guide the upper seal half into place.

    One tip on the seal...line up the seal halve ends so they are NOT in line with the filler block split line. I put mine so the seal was canted about ½ inch to one side.

    This procedure was told to me by a gentlemen who owned the biggest engine rebuilding place around here...he remembered this method from working on them back then. He has since passed on but I was glad to meet him and hear his advice...he was glad to help...though the guys in the shop when I walked in kind of freaked. "You are here to see who?" "Does he know about this?" "Are you sure?" They were very surprised when he came out and took me in his office, waxing about the old days and how he hadnt seen one in years, etc.

    Procedure worked like a champ for me...though he did say, every now and then one was super stubborn and they had to drop the mains a few thousandths in order to get the upper half done.

    If anything isnt clear, just ask!

  3. #3
    Join Date
    Jul 2007
    Location
    Rhoadesville, Virginia (five miles from no place)
    Posts
    5,125

    Default

    You may want to check with a local NAPA. They used to sell a "rear main seal installation tool kit" through the K-D tools line. It had a few little items that help install the old style seals without damaging the crankshaft seal surface.
    "Free advice is worth what you pay for it."™

  4. #4

    Default

    All thats needed is a long brass drift .One thing I will have to say is who ever designed the motor was thinking when they designed the rear seal . I have replace mine in the vehicle, and it one of the easiest thing to do.The only pain is the oil dripping off the block after the pan is removed.

  5. #5

    Default

    I have done mine. I was able to remove everything with a drift and visegrips. I installed the seal by pushing it into the upper groove by hand and gently tapping till it was home. If I remember correctly it looked a bit tight for a Chinese handcuff type of seal puller. It was not a difficult job, just upside down and oily as mentioned. I wish I had done what Brute said. I did use some carefully placed sealant. Mine still leaks a bit. I do run synthetic though. My future fix is a rebuilt replacement swap. I don't want to do the seal again.

    If it is not a bad leak I would leave it. Unless your bored.
    Liz, covid, murdered 10/19/21

  6. #6
    Join Date
    Sep 1998
    Location
    North Central Wisconsin
    Posts
    11,520

    Default

    On the dripping oil...if you can...take the pan off the day before and leave it off to drop overnight...I did that and it didnt drip much at all...was time for and oil change anyway, that just made it easier.

  7. #7
    Join Date
    Jul 2007
    Location
    Rhoadesville, Virginia (five miles from no place)
    Posts
    5,125

    Default

    Quote Originally Posted by brute4c View Post
    On the dripping oil...if you can...take the pan off the day before and leave it off to drop overnight...I did that and it didnt drip much at all...was time for and oil change anyway, that just made it easier.
    Good idea. Its always nice to really wash out the oil pan once too....makes for a good start again.
    "Free advice is worth what you pay for it."™

  8. #8

    Default Thanks

    One tip on the seal...line up the seal halve ends so they are NOT in line with the filler block split line. I put mine so the seal was canted about ½ inch to one side.
    Not sure I understand this part. The rest is pretty much what I remember. Why are there 5 pieces to the rear seal set? Probably the difficult part will be finding an oil pan seal. Thanks for all the help.

  9. #9
    Join Date
    Sep 1998
    Location
    North Central Wisconsin
    Posts
    11,520

    Default

    The rear main seal has an upper half anda lower half. The upper halfgoes up into the block over the top of the crankshaft. The lower half fits in the filler block that bolts up from the bottom. The parting line at the top of the filler block, where it bolts onto the motor...dont have the rear main seal halves parting line on the same line as the filler block to engine block parting line.
    Since the filler block line is fixed, clock the rear main seal halves to offset them from the filler block parting line...he told me this was helful in preventing leaks on the 230's seal.

    I hope thats clear...

  10. #10

    Default

    This might be what brure4c is describing. The illustration for a GM pickup shows it clocked one half inch.


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