Distributor leaking oil on intake - Team Camaro Tech
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post #1 of 14 (permalink) Old May 28th, 02, 10:59 AM Thread Starter
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I am just looking for some ideas. The problem is that at higher RPM, above 5K, I am pushing oil out onto the intake from beneath the distributor. The leak appears to be around the gasket between the distributor and the intake.

The engine is a 400 at about 12 to 1 compression. The distributor is new. Oil pressure is about 65 lbs. I have installed a crank case vent system to the headers. Until I did this I was pushing oil out at the valve covers as well. I have verified the distributor will go all the way down by inserting it with no gasket. I tried gaskets painted with silver paint. This worked the best, but glued the distributor down. I tried a 1/16" rubber plumbing gasket from the hardware store. This worked fairly well, but still leaked.

What do you guys think of doubling up gaskets? Besides crank case back pressure, what else could cause this problem? Does anyone have any suggestions as to what types of gaskets may seal better?
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post #2 of 14 (permalink) Old May 28th, 02, 11:07 AM
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Try Hylomar gasket dressing from Permatex....use it on all contact surfaces. It usually repells oil. Then make sure the distributor is cranked down tight.

If that failed, then I would go to silcone adheasive sealant. I know that will stop it.

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post #3 of 14 (permalink) Old May 28th, 02, 01:32 PM
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wow thats a lot of pressure even with the evac system did you use a windage tray? that oil must be realy foamin if not, the hylomar should work but i think you will find a leak somewhere else with that much pressure. what kind of dist did you use.
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post #4 of 14 (permalink) Old May 29th, 02, 02:52 AM Thread Starter
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I do not have a windage tray. I have looked pretty close and do not see any other leaks or seeping. Both mains, the fuel pump and pan are all dry. The distributor is a big cap Proform replacement. Please help clarify what "Hylomar" gasket dressing is. Is that the black stuff that stays sticky and is also referred to as shellac? Also the evac system shows no sign of any oil in the valve cover filter caps or hose. That surprised me somewhat so I checked and I do have good vacuum at both hoses.
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post #5 of 14 (permalink) Old May 29th, 02, 04:30 PM
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What kind of "crankcase vent system to the headers" do you have? You obviously have high pressure in the crankcase that's blowing oil out - I've never seen a distributor base oil leak in 40 years of building small-block Chevys. Venting to headers only works when there is no restriction downstream of the headers so scavenging comes into play - with a street exhaust system, there is no scavenging action, so you're blowing pressure waves back into the crankcase. Junk the open-headers race-car "vent" system and use the stock PCV setup and your oil leaks will stop.

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[This message has been edited by JohnZ (edited 05-29-2002).]
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post #6 of 14 (permalink) Old May 30th, 02, 12:58 AM
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John has a very good point. There is no "scavaging" effect at street rpms anywho. Dump the headers....it's the problem.

Just as a followup, Hylomar HPF is a gasket dressing gel that is made by Permatex and available at most automotive outlets. I prefer the tube for small gaskets, and is in the usual Permatex small "toothpaste" tube part number 25249. The stuff even looks and feels like toothpaste gel, but is impervious to oil and will make gaskets seal better and come right off if you need them to.

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post #7 of 14 (permalink) Old May 30th, 02, 03:40 AM Thread Starter
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In order of success, from least to best, here is what I have tried for crank case ventilation.

Normal PCV system with a breather on one valve cover and the PCV on the other. Works poorly at high RPM due to lack of vacuum. There was oil vapor venting from the breather as well.

No PCV and breathers on both valve covers. Works fairly well but can be messy. Efficiency was cut when the breathers were piped into the air cleaner to keep the valve covers clean. I also had to gut the foam material from the breather caps after piping to the air cleaner.

No PCV and Mr. Gasket header ventilation system. Works the best so far. The engine is sealed except for the two breathers connected through check valves to headers. I use a 3" exhaust system with Flowmaster 40's. There is virtually no back pressure and it has excellent vacuum at both hoses, at least at an idle. The Mopar style breathers do have filters in them that reduce airflow though. I may try my other "gutted" breathers.

Currently I have no oil leakage unless I am under WOT and above 5K rpm. For the most part I had no leakage from any of the ventilation systems I have tried unless I was WOT at 6K.

JohnZ, I agree with your statement. I have put together a lot of small blocks, but this is the first 400, and I have seen crank case pressure but have never seen a leak like this at a distributor. Please keep the ideas coming, I never discount any of them.

I may not be able to read any replies for a few days. At 5:30 AM tomorrow I head for Joliet to the Spring Nats. Anyone else going to be there?
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post #8 of 14 (permalink) Old May 30th, 02, 08:10 PM
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I had a crankcase pressure problem where it was fine at idle or free revving, but underway it would force oil out of the seals and even blew a piece of oil pan gasket out near the starter!

I eventually found a broken ring land between top and second ring. The rings were hand gapped to minimum spec, and the engine got hot a couple of times and I think the ends butted and kinda stuck the ring in the bore, breaking the land.

Of course any 400 has cylinder roundness problems. Hopefully yours was bored and honed with a block plate?
David

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post #9 of 14 (permalink) Old Jun 3rd, 02, 06:17 AM Thread Starter
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I have discovered one thing new. I was setting the timing and had the engine at 3K. I noticed some oil starting to seep from the bottom of the distributor as it has in the past. I had the distributor loose, but not real loose, just enough to be able to turn it. I pulled the breather caps and there was no crank case pressure at all under these conditions. This would tend to make me believe this is not a crank case pressure problem after all. Now what do you guys think?
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post #10 of 14 (permalink) Old Jun 3rd, 02, 11:18 AM
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Ummmm....just a guess.....I would pull the "new" distributer and measure the diameter of the lower part of housing where the the distributer housing "seals" the lifter gally oil passages.....I don't have a measurement in front of Me, but just compare it to another distributer....... (possibly the distributer housing is not machined correctly?, even though Your oil pressure sounds good...)
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post #11 of 14 (permalink) Old Jun 3rd, 02, 12:46 PM
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Hey Chris, I have to agree with checking the diameter of the distributor where it fits in the manifold. I've seen this before on 350's , I want to say around 1988 or 89 to 1991 there was a change in distributors in B body cars. One had a smaller diameter base and would fit and work in a larger hole manifold but would leak oil out down the bell housing. Trust me when I say an experienced mechanic wouldn't be able to tell if the parts counter person gave him the wrong one because you can't tell looking down at it in the motor. I found this problem on a car once and the oil leak was because of the wrong distributor. I think 89 because that was the first year for fuel injection on B bodies. 1991 changed because the body style changed and an 89/90 distributor is longer and won't fit in a 1991 B body because of firewall clearance. Real fun GM engineering stuff, huh ? Anyhow, thats worth a look see.
Hope this helps.

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[This message has been edited by drew69 (edited 06-03-2002).]

[This message has been edited by drew69 (edited 06-03-2002).]
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post #12 of 14 (permalink) Old Jun 4th, 02, 03:01 AM Thread Starter
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Thanks guys, I will pull the distributor and mic it tonight then compare it to an old one I have laying around. Any idea how much difference there was between the two?
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post #13 of 14 (permalink) Old Jul 2nd, 02, 05:31 AM Thread Starter
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Well… Here are my last findings. I measured the old and new distributors and they are the same. When I went through my distributor gaskets I did find some that were too small to fit my distributor so I can guess what size the smaller one is.

The problem is definitely crank case pressure. I tested with a 3' piece of hose connected to my dipstick tube with the other end rubber banded into a wadded up rag. When I wound it up there was all kinds of oil in the rag. The only part that bugs me is why this crank case pressure does not seem to vent to the top of the motor very well. In other words I get very little pressure inside the valve covers.

I think I am going to have to pull the motor apart and look for out of round cylinders or a broken ring. Not something I wanted to do real bad, but maybe it is time for that roller cam I have been looking at.
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post #14 of 14 (permalink) Old Jul 2nd, 02, 07:18 PM
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Do a leak down test to see how good a ring seal you have.
My 400 had 60% leak down! I saw light and dark stripes on the cyl walls due to distortion of the cyl head bolts.
David

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