SBC oil pan gasket puzzler

Discussion in 'Engine Topic' started by Jeep43, Dec 30, 2017.

  1. Jeep43

    Jeep43 Veteran Member

    1,028
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    Mar 30, 1999
    Connecticut
    I have a strange issue trying to seal up an SBC project I have. The block is a 2pc 1970 010 block. The pan is a Milodon 6qt pan for a 2 pc seal P/N 30401 which is for 55-79 blocks. I first went to assemble with a new blue Felpro 1pc main gasket, OS34510T which has provisions for either side dipstick but is made for 2pc seal blocks. When I fit it, the arch that went over the timing cover pressed in place and fit nice and snug. The arch that traveled over the rear cap was loose as heck. When I pressed the little molded wedges into the pockets on either side of the cap, the gasket had daylight between it and the cap never mind getting into the cap groove. I didn't even want to try installing it.

    I then ordered a Milodon 41000 1 pc gasket. It fit better but still had slack in the arch area that traveled over the cap. I installed it anyway with just a dab of silicone at all 4 corners and torquing properly but after priming the engine, I find a little puddle of oil on the floor. After some probing I see its definitely seeping from the pan gasket and since its leaving a puddle from just lifter valley drain back, I presume is a big leak. I can take a scribe and wiggle the gasket around between the pan and the cap. I can also slip a .006 feeler gauge in between the pan and the gasket with almost no effort.

    Milodon says maybe its the pan and exchange if for an new one although I would think an improperly stamped pan would look funny, the die would have to be really screwed. The fact that both the Felpro and Milodon silicone gaskets were loose over the rear cap points me to the cap, not the pan but am not sure how that can happen....

    Has anybody seen anything like this? Its not my first SBC build but it has been years and I have never used the 1 pc gaskets before. I want to check to see what I am missing before I go and install a multi-piece felpro with lots of spray cheese ultra RTV......
     
    Last edited: Dec 30, 2017
  2. cadillac_al

    cadillac_al Veteran Member

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    Apr 22, 2015
    Maine
    I have used a few one piece gaskets and never seen the problem you described. They were fel pro blue ones. I think once I got one with only one dipstick hole but not positive. It sounds like something is going on with your rear cap but I have never heard of it. The gasket should fit nice and tight in the groove. Usually the problem is on the timing cover side but not the rear main cap. If it happened to me I guess I would yard out another engine to compare with.
     
  3. Jeep43

    Jeep43 Veteran Member

    1,028
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    Mar 30, 1999
    Connecticut
    I pulled it apart and ruined the milodon gasket. I bought a multi piece gasket to compare. First I set the pan on the engine with no gasket to observe the arc around the cap. It seemed OK. I then tried my blue 1 pc felpro and noticed that although it was loose around the main cap, the arced portion was much thicker. The thickness of the milodon arc was about the same as the felpro multi piece. .250" or so. The felpro blue however is .320. I dry fit the 1pc blue felpro and definitely noticed that there was a lot of compression in that area (the silicone was much harder under compression. I'm going to install the felpro and cross my fingers. For insurance purposes I'll run some ultra black not only in the 4 corners but around the timing cover and main cap gasket grooves.
     
  4. Damon

    Damon Veteran Member

    12,937
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    Nov 16, 2000
    Philly area
    The gasket thickness at the rear main cap has been the same since half of forever. At the front (timing chain side) there were two different ones- thick and thin (depends on the oil pan, not on the timing chain cover). Not sure why you are having problems.
     
  5. Jeep43

    Jeep43 Veteran Member

    1,028
    12
    Mar 30, 1999
    Connecticut
    Correct, that's why its a puzzler. I installed the Felpro and it seems pretty good. I'm going to chalk my experiences with the milodon 1 pc gasket to a tolerance stackup issue and move on.
     

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