oil leak with crankcase vacuum

Discussion in 'Troubleshooting & Diagnosis' started by pomartin, Jun 5, 2021.

  1. pomartin

    pomartin Veteran Member Gold Member

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    Dear all,

    I'd need some opinion...

    On SBC 383 stroker I'm battling what appears to be rear main seal or rear oil pan leak for almost a year now...

    - I made sure valve covers, china wall and manometer tubing is not leaking.
    - I replaced 2PC RMS number of times, with and without mating surface offset, with and without sealant on the mating surface. The sealing lip was oriented correctly.
    - I always applied sealant around high pressure port on rear main bearing cap (loctite 574)
    - I also replaced fel-pro 1 PC oil pan gasket multiple times.
    - Then I replaced oil pan (previously Summit 7qt now Milodon 30900 7qt) and used Milodon 1PC gasket.
    - I use 5QT of oil in 7QT oil pan
    - My latest attempt was creating 7InHg vacuum in the crankcase- still leaking.

    The vacuum attempt seems a bit odd to me... due to the fact that there is a leak and vacuum in the crankcase I'm thinking that leak is coming from the high pressure port in the rear main cap... what do you think about this one?

    The engine has 70 psi of oil pressure on cold idle, 30psi on hot 750RPM idle and pressure relief is set at 70psi.
    Oil is rotella 15w40... lifters seems to love it.
    There is no visible scratching on crank surface.

    It is a minor leak, but it is driving me nuts... I hate leaks :crazy:

    Thanks in advance,
    M
     
  2. tom3

    tom3 Veteran Member

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    First thing I'd suggest, grab the front balancer, push/pull, check for end play on the crank. The thrust flange can wear, cause some weird stuff. Seems like you've done everything else?
     
  3. biker

    biker Veteran Member

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    That's a lot of oil pressure. And really heavy oil. When u say the lifters love it....do u say that because they are quiet? Quiet lifters aren't a measure of proper viscosity. If you have a consistent vac in the crankcase, I wouldn't suspect the pan gasket. Can you hold that vac at wide open throttle?
    Sounds like you probably have a hv/hp oil pump. Combined with the heavy oil, your engine, cam/dist gear and oil pump drive are working really hard. Probably needlessly.
    So, that leaves u with the rear main seal, but it sounds like you are pretty good at installing that by now. You sure the oil pressure sending unit and distributor gasket aren't leaking and running down? Some day in the oil would help you focus on the exact place it is leaking.
    I feel your pain, I hate leaks too.
     
  4. pomartin

    pomartin Veteran Member Gold Member

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    Thank you for your input tom, much appreciated.
    I'll perform measurement on monday, as I can borrow better measurement tools at work.
    It should be within 0.003"-0.011" range, correct?
     
  5. pomartin

    pomartin Veteran Member Gold Member

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    Thank you for your input, much appreciated :)
    Yes, by loving I mean hey are quiet.
    Vac at WOT drops to 4 InHg. But even when just cruising around and maintaining 7 InHg in the crankcase the leak appears.
    Oil pump is M55HV- marking on the pump case. I am not sure of pressure regulator spring, but measurement shows it opens at 70PSI.
    I'm sure about top-end leaks. Dry as a bone, confirmed with chalk spray to notice oil more easely.
    I tried 0w10 in the past with different lifters, but had this leak too...

    Is it worth trying replacing the pump with original one?
     
  6. biker

    biker Veteran Member

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    Well, even if vac is zero, there is no pressure to push past a gasket. Have you looked into a different brand or style or rms? I dont know how much mileage is on your engine, but the seal hasn't grooved the crank has it? Maybe try a seal with an offset lip that seals on a different part of the rear journal surface?
     
  7. pomartin

    pomartin Veteran Member Gold Member

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    Thanks for suggestion.
    As far as I can tell there is no groove on the crank. So far I only tried with Felpro 2900.
    I'll order the one with offset to try it out.
    Is there any major difference between silicone and viton rear main seals?
    Mileage is unknown...
     
  8. biker

    biker Veteran Member

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    I've only ever used the blue felpro silicone ones, never had a leak. I see summit has some reviews that say the viton ones leak. But that is not personal experience.
     
  9. pomartin

    pomartin Veteran Member Gold Member

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    Once again I dropped the pan...
    After a closer look I can notice the "sealing ring" (red arrow pointing to it) on the crank, but it is not detectable with a finger... nontheless I decided to give a offset lip a try.

    [​IMG]

    Crank play seems to be ok at 0.005".

    There was quite some oil between the dust lip and seal lip of my old RMS. Does this mean that the leak was indeed caused by RMS? The bell of the transmission is also a bit oily.
    Sorry for bad image... looks like I dod not manage to take a better one.

    [​IMG]

    There is also a "plan B"... as ashamed as I am of it, I decided to craft a "engine daiper"...
    Hopefully this time the leak will stop so I will not have to use it :D

    [​IMG]
     
  10. pomartin

    pomartin Veteran Member Gold Member

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    Engine is back in place.
    This time I used felpro 2PC RMS with offset sealing lip and without offseting the RMS.
    While installing I cleaned the RMS bead and greased sealing lip and crank surface.
    I added a thin layer of ultra black on mating surfaces of RMS pieces (not on lip itself) and on mating surfaces between rear main cap and block.

    After a short test drive there is no leak visible. I'll repeat test tomorrow with a longer drive and see what happens.

    Thank you all for your input so far.
     

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