Register now to get rid of these ads!

Preventing SBC Rear Main Oil Leak - What is the Trick???

Discussion in 'The Hokey Ass Message Board' started by fiftyv8, Jan 17, 2013.

  1. fiftyv8
    Joined: Mar 11, 2007
    Posts: 4,789

    from CO & WA

    Anybody out there gone any tried and proven methods to deal with leaking rear main seals in SBC engine.

    I have one right now that was OK for a couple of hundred miles.
    I fitted a new gasket etc and went to a lot of trouble I thought to get the tin oil pan fitted up good, but still it is leaking now.:confused:
  2. KJSR
    Joined: Mar 7, 2008
    Posts: 2,161

    from Utah
    1. Utah HAMBers

    Don't ever put oil in it:D

    I have yet to have one that didn't leak. I'm hoping my new roller block with a one peice seal will have better luck.
  3. dreracecar
    Joined: Aug 27, 2009
    Posts: 2,846

    from so-cal

    Rotate the seal 1/4"-3/8" so that the seal split is different then the main cap split
    falcongeorge likes this.
  4. racemad55
    Joined: Dec 14, 2005
    Posts: 1,149


    Sure it's the seal and not the oil pan?
    Register now to get rid of these ads!

  5. oj
    Joined: Jul 27, 2008
    Posts: 6,155


    What i do is when assembling you are able to see what is what back there and if there isn't any crush i shear a piece of brass shim stock - .002ish - and slip it in behind the seal and it effectively moves it closer to the crank. Lots of time when you get a motor alined hones you have to pay special attention to the rear seal. In fact FelPro makes a special seal #2909 for align honed 400 blocks.
    lothiandon1940 likes this.
  6. 53sled
    Joined: Jul 5, 2005
    Posts: 5,820

    from KCMO

    Use an 86-up core. :)
  7. mutant55
    Joined: Mar 11, 2012
    Posts: 176


    Rotate slightly so the split is different like dreracecar said, and maybe add a tiny spot of silicone to the ends of the seal halfs where they mate, I have good luck with that. I also turn the seal around sometimes (run it backwards) like on my race motors where I have a lot of crankcase vacuume and the pan evac pulls the seal in to the crankshaft, but it's not for everybody!
  8. Mr.Musico
    Joined: Jan 7, 2007
    Posts: 1,576

    from SoCal

    make sure the seal was installed correctly (isnt backwards)
  9. Keep
    Joined: May 10, 2008
    Posts: 662


    I just went through this ordeal with mine. Here is what I learned.

    1 - make sure its not the oil pan. I will repeat that again, make sure its not the oil pan. This turned out to be my problem after replacing the rear main 4 times.
    2 - install that damn seal the right way.
    3 - a little gasket sealant on the rearmain caps works wonders
    4 - get the felpro one piece oil pan gasket

    Get the felpro seal and oil pan gasket, dont try and cheap out you will just replace the damn thing again.
  10. wingman9
    Joined: Dec 30, 2009
    Posts: 804

    from left coast

    I have 6 cars of various makes that all have sbc motors and doing this keeps them from leaking. I hope I didn't just jinx myself.
  11. brigrat
    Joined: Nov 9, 2007
    Posts: 4,813

    from Wa.St.

    Flattening out your pan bolt hole helps get a better crush also.................
  12. Fat Hack
    Joined: Nov 30, 2002
    Posts: 7,709

    Fat Hack
    from Detroit

    Anymore, the one piece rear seal blocks are the way to go...thousands of affordable cores out there to work with and a big step up in the rear main seal department.

    That said, I've never had an issue when using the good Fel-Pro two piece rear seal kits (the blue coated ones). Installed correctly with a dab of black rtv at the joints has been my method for years with no leaks.
  13. captmullette
    Joined: Oct 15, 2009
    Posts: 1,929


    ive gone thru the same thing, new oil pan with felpro blue 1 piece and rtv, leaked. put the old pan back on with the old style cork , leaked, bought a new aluminum pan with a new blue felpro, frigging thing leaks, the hell with it........ , i dont have a lift, just a concrete floor......
  14. aaggie
    Joined: Nov 21, 2009
    Posts: 2,527


    Use a hammer and dolly to get the pan surface flat then wipe the pan rails and gasket surfaces down with slovent to get any residual oil off. Put a small drop of black rtv on the mating surface of the seal halves and torque the rear main down. Apply some black RTV to the corners where the gasket meets the block and install the pan bolts.

    Use the Fel-Pro one piece gasket that matches your oil pan and don't overtighten the pan bolts. The gasket is expensive, about $30 but well worth it. I have reused them several times so they are cheaper in the long run.
  15. fiftyv8
    Joined: Mar 11, 2007
    Posts: 4,789

    from CO & WA

    I installed my gaskets and oil pan while the engine was out of the vehicle on an engine stand.
    Knowing alot of folks have issues with the rear main leaking, I took extra time and care to ensure everything was fitted up snug with sealant etc and I dont believe I got the seal in wrong so I guess I am looking at a Felpro gasket swap out then.

    It sure ain't going to be easy no the engine is installed...

    I see on some of the aluminum oil pans sold they recommend slightly grinding the end seal curvature to get it to fit better.
  16. There is a thread- " Main Bearing Wear Pattern " up right in front of yours. check out my post # 10, and this should help you as well, good luck, TR
  17. fiftyv8
    Joined: Mar 11, 2007
    Posts: 4,789

    from CO & WA

  18. groundpounder
    Joined: Jul 1, 2010
    Posts: 260

    Member Emeritus

    Hey all these guys are right on the money!....check your oil pan bolt holes to make sure they are not dimpled in or towards the gasket,..using a ball peen hammer to push the thru holes back the bolt draws up the pan to gasket. Filing the parting lines of your main bores and deburring the block/ caps very important... Making sure when you push in or snap in your bearing shell that it doesn't gouge the shell when installing. A light film of Black Rtv between main cap and block,...just by seal area and clocking the seal halves a little bit...making sure the seal is installed right!...the rear main and all caps should snap in...fiftyv8 says ( block register)....very important. Any cap walk...baadddd! will see galling on both the cap and block mating surfaces if cap walk is evident...not mentioning loose caps ( or a widened block register) and last of all , don't forget to set your main bearing thrust!....some rear mains have dowel pins and some don't. Some bearingwear patterns are from cranks being machined as far as .0004 to.0006 journal run out....this is measured by an Arnold gauge....or a really good Machinist!...
    Last edited: Jan 17, 2013
  19. 68vette
    Joined: Jul 28, 2009
    Posts: 306


    I have built two 305 chevy engines...the older 2 piece seal ones. I do not off set the seals....put the lip facing the front of the engine as my ol mechanic says...and I use some sealer...the red kind on the mating surfaces...then put the red gasket maker on the oil pan gaskets where they meet the edges....I am saying all of this being it was 2003 when I built the last engine....I am now in process of building my 283 for my a nice reminder to me here to be careful with that rear seal...I use Fel Pro gaskets and the orig oil pan with the holes beat back down.

    Forgot to add....never had a rear seal leak....I think I also put a little oil on the lip of the seal before assembly....can't remember for sure.
    Last edited: Jan 17, 2013
  20. McDeuce
    Joined: Sep 16, 2008
    Posts: 258


    I like using the new Felpro one piece oil pan gaskets,
  21. Model A Vette
    Joined: Mar 8, 2002
    Posts: 1,055

    Model A Vette

    I have only seen the one piece oil pan gasket available for an engine with a thick front seal. Is there one available for the thin front seal?
    What was the year for the change from thin to thick?
    Was the pan or the timing cover changed or both?
    From what I can determine the aluminum pan uses the thin seal.
  22. 39 Ford
    Joined: Jan 22, 2006
    Posts: 1,558

    39 Ford

    All these suggestions are good just want to add, check your oil pressure, high pressure causes leaks 25-30 psi at idle is enough.
  23. 68vette
    Joined: Jul 28, 2009
    Posts: 306

    68vette ol mechanic, Arthur says too much oil pressure wears out the galleys among the other things....says look at water pressure when it runs thru rocks fast....they turn smooth....says lower oil pressure better than high oil pressure.
  24. fiftyv8
    Joined: Mar 11, 2007
    Posts: 4,789

    from CO & WA

  25. inliner2318
    Joined: May 9, 2008
    Posts: 296


    had mine leak at the back of pan. gasket was too thin and new pan didnt match perfect. thick cork. i only buy felpro gaket kits. best gasket is crap.

    all above is good advice.

    some people put a small knurl on main seal crank surface too.

    don't see how it helps?
  26. rd martin
    Joined: Nov 14, 2006
    Posts: 2,289

    rd martin
    from indiana

    Dam, i always throught gm small blocks were made to leak oil! Scratch that one.
  27. KeithDyer
    Joined: Mar 26, 2007
    Posts: 193


    A PCV system will keep the oil in the motor (I know . . . , not traditional but effective).

    Will also help keep oil from going past the valve guides at idle.

    Vacuum is your friend in this case.

    Take care, K
  28. porknbeaner
    Joined: Sep 12, 2003
    Posts: 41,124


    Look at the crank and see if it is worn where the seal meats up with it. they make an offest seal to over come that problem.

    Rotating the seal and or a dab of silicone is also a good trick as has been mentioned already.
  29. 432bullet
    Joined: Sep 14, 2009
    Posts: 51


    Sold it ,Bought a ford. True story.
  30. dirty old man
    Joined: Feb 2, 2008
    Posts: 8,240

    dirty old man

    I think I remember seeing both thick and thin end seals available on the one piece Fel Pro sets when I looked recently on Summit. Maybe check on Fel Pro site?

Share This Page

Register now to get rid of these ads!


Copyright © 1995-2020 The Jalopy Journal: Steal our stuff, we'll kick your teeth in. Terms of Service. Privacy Policy.

Atomic Industry
Forum software by XenForo™ ©2010-2014 XenForo Ltd.