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  1. #1
    Join Date
    May 2003
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    St. Charles, Mo
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    419

    Default Big Block Chevys and Oil Leaks

    I have a Mark IV big block Chevy and can not fix an annoying leak. It shows up worse after hard acceleration. The oil spays oil over the passenger side of the engine compartment and even on the underside of the hood. It then drips from every part of the engine and tranny. I've changed the harmonic balancer seal twice and the pan gasket three times with no success. The oil seams to be hitting the harmonic balancer and slinging oil to the passanger side of the engine bay. It seams like the likely canidates are the oil pan gasket and the harmonic balancer seal.

    The harmonic balancer is a Fluidamper and is new. The oil pan is a Moroso 9 quart pan with the one piece silicone gasket. I am running a PCV valve plumbed to the plenum. I tried using silicone sealant around the timing chain cover to pan area of the gasket. It didn't work.

    I was wondering if anyone tried using an electric vaccum pump to evacuate the crank case pressure. I could make an accumulator for the oil to seperate and return to the pan. This leaking is getting real old though.

    Anyone have simliar problems and have any cures?

    Thanks,
    Dennis



  2. #2
    Join Date
    May 2005
    Location
    Fontana, CA
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    Default

    Many BBCs I've seen before had a lot of crankcase pressure and usually just blew it out of the breather. Seemed a good PCV and breather always helped out. With that large a pan is there a windage tray as well? That can also help with a lot of flying oil and pressures.
    Nick R.
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  3. #3
    Join Date
    Mar 2005
    Location
    Detroit Subs
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    201

    Default

    Make sure you have a short bolt with sealant in the front of the block where the fuel pump pushrod passes through. Crankcase pressure can build up and force oil out that hole - then it hits the balancer and then the fan(s) blow the oil everywhere. I have been in that situation and it took a long time to discover where the oil originally came from. Best of luck!

  4. #4
    Join Date
    Sep 2006
    Location
    Jasper, IN
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    2,299
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    The guy that dyno'd my engines told me that a BBC needs to have at least four valve cover breathers (two on each side) to properly vent the crankcase - unless you're using a vacuum pump. Food for thought.
    Herb Lumpp
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  5. #5
    Join Date
    Jul 2006
    Location
    Tallahassee
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    285

    Default

    Big Block here (1972 Gen IV 396), I have a single breather on the driver's side, and a PCV valve on the passenger side.

    I haven't lost a drop in 2 years.

  6. #6
    Join Date
    Aug 2001
    Location
    Connecticut
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    1,510
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    Default

    If the oil is all to the passenger side of the motor, I'd suspect the balancer seal; I've had it happen on a brand new motor one time too... not fun but not the hardest thing to replace either, just borrow a good balancer puller/installer. Have you tried a differnt type of balancer seal? I noticed their are different grades and quality of seals, some are single lip, better ones are double or triple seals, etc. Also it is critical that the seal be in square/straight
    1968 Camaro RS/SS, LS7 with Katech mods, T56 Magnum, C6Z06 Brakes
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  7. #7
    Join Date
    Aug 2004
    Location
    CHICAGO SUBURBS
    Posts
    761

    Default

    For a couple of years Fel-Pro balancer seals have been made too loose for small and big block Chevy's. If you take a new seal and a balancer off the car, you can see when installed on the balancer if you move it any little bit off center, you can see daylight. I found this out after changing seals and balancers to stop 2 different leaks. The fix is get a GM or other seal, test fit it on the balancer, puhing it off center. The other way take the spring out of the seal and shorten it some. That is trial and error to get the right amont of drag. The spring is tapered on one end and is just wound together. As long as you unwind it you can trim the big end and put it back together. That fix was found with an internet search. I've done both and no more leaks!

  8. #8
    Join Date
    Aug 2001
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    931
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    I chased the same thing on the Red Witch when I first bought it. Finally had it up on a lift with someone revving the engine and a flashlight underneath. Spotted oil coming from a pan bolt at front of engine right next to the balancer on the right. Pulled the bolt, glued the crap out of it and leak went away. Having everything clean and up on the hoist made all the difference. When you solve your problem, let us know what it was.

  9. #9
    Join Date
    May 2003
    Location
    St. Charles, Mo
    Posts
    419

    Default Oil leaks

    Thanks for the info guys. I'm going to pull the engin out of the car this winter hand have it tuned on and dyno. At that same time I'll look try to find the leak. I've pull the pan off three times now with th engine in the car and it's not much fun. Pulling the balancer off isn't too bad. I've only noticed the oil leak after a hard acceleration. If I just cruise around, I don't have the problem, so you can imagine I have the problem just about everytime I get in the car.

    I'll bring it into work some day and put it on a lift rack and check it out as well.

    Thanks again.
    Dennis

  10. #10
    Join Date
    Sep 2006
    Location
    Henderson,NV
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    2,917
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    On tough oil leaks a die is a good idea. You can get die that reacts to a black light from the gm dealer. Then all you need is a black light bulb for your drop light. Makes it much easier to figure out where the leak originated from.
    Todd

  11. #11
    Join Date
    Mar 2005
    Location
    Detroit Subs
    Posts
    201

    Default

    It is pretty easy to take a 3/8" bolt, put a little silicon on the threads and screw it into the top hole at the front of the block by the fuel pump. Your description of the problem and when it occurs really points to oil being forced out of the front hole that gets used to hold the fuel pump pushrod in place whil changing the fuel pump. That passage is just open and is not much higher than the oil pan. Try it and get on it -what do you have to lose?



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