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Old 04-22-2012, 03:36 PM
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Pesky Oil Leak

I've been trying to find an oil leak that has plagued my chevy 406 since its build 3 years ago. I have changed intake gaskets 3 times, dizzy gaskets several times as well as different materials and thicknesses, valve cover gaskets 3 times as well, the oil pressure fitting is dry as is all the other things listed above. I have oil that runs down the passenger side of the back of the block, drips down onto the starter and runs down to the starter bolts and off the bolts onto the exhaust pipe. My question for anyone who know is this, is there an internal oil passage that runs on passenger side of the block at the back? I had the car running the other day and it is on some jack stands and I saw oil ozzing out from under the bolt head that is 2nd one up from starter. The oil was running off that bolt down to bolt below it and down onto the starter to its bolts. I pulled the bolt out and found the threads wet with oil. I found no oil from the intake or oil pressure unit, drivers side is dry. Rear seal appears to be dry, oil is only appearing on the outside of the trans bellhousing cover. Anyone have any other ideas or is the an oil passage that may be causing it? I cleaned the bolt and put some thread sealant and reinstalled but have not had it running yet since I am working on the exhaust right now.

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Old 04-22-2012, 05:04 PM
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Quote:
Originally Posted by cc82z-28
I've been trying to find an oil leak that has plagued my chevy 406 since its build 3 years ago. I have changed intake gaskets 3 times, dizzy gaskets several times as well as different materials and thicknesses, valve cover gaskets 3 times as well, the oil pressure fitting is dry as is all the other things listed above. I have oil that runs down the passenger side of the back of the block, drips down onto the starter and runs down to the starter bolts and off the bolts onto the exhaust pipe. My question for anyone who know is this, is there an internal oil passage that runs on passenger side of the block at the back? I had the car running the other day and it is on some jack stands and I saw oil ozzing out from under the bolt head that is 2nd one up from starter. The oil was running off that bolt down to bolt below it and down onto the starter to its bolts. I pulled the bolt out and found the threads wet with oil. I found no oil from the intake or oil pressure unit, drivers side is dry. Rear seal appears to be dry, oil is only appearing on the outside of the trans bellhousing cover. Anyone have any other ideas or is the an oil passage that may be causing it? I cleaned the bolt and put some thread sealant and reinstalled but have not had it running yet since I am working on the exhaust right now.
Have the heads been angle milled by any chance? Sometimes this leaves a slight opening at the uppermost part of the head towards the intake that mates to the block. It don't seal the upper most part of the head gasket to the block which leaves a space for oil to seep out from under the intake and run down the head and block mating surface.
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Old 04-22-2012, 05:10 PM
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Are you using the gaskets that come with the kit for each end of the intake ?
Or did you discard them and go with a good silicone for the ends ?
I alway's do away with them and run a bead of sicilicone on each end and let it sit for a bit before siting the intake in place JMO it has alway's worked for me anyway IMHO



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Old 04-22-2012, 05:45 PM
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Quote:
Originally Posted by cc82z-28
I've been trying to find an oil leak that has plagued my chevy 406 since its build 3 years ago. I have changed intake gaskets 3 times, dizzy gaskets several times as well as different materials and thicknesses, valve cover gaskets 3 times as well, the oil pressure fitting is dry as is all the other things listed above. I have oil that runs down the passenger side of the back of the block, drips down onto the starter and runs down to the starter bolts and off the bolts onto the exhaust pipe. My question for anyone who know is this, is there an internal oil passage that runs on passenger side of the block at the back? I had the car running the other day and it is on some jack stands and I saw oil ozzing out from under the bolt head that is 2nd one up from starter. The oil was running off that bolt down to bolt below it and down onto the starter to its bolts. I pulled the bolt out and found the threads wet with oil. I found no oil from the intake or oil pressure unit, drivers side is dry. Rear seal appears to be dry, oil is only appearing on the outside of the trans bellhousing cover. Anyone have any other ideas or is the an oil passage that may be causing it? I cleaned the bolt and put some thread sealant and reinstalled but have not had it running yet since I am working on the exhaust right now.
Using the image below, what bolt did you remove that had oil on it? None should have had oil, are you sure it wasn't coolant or ATF?

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Old 04-26-2012, 06:01 PM
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Quote:
Originally Posted by cobalt327
Using the image below, what bolt did you remove that had oil on it? None should have had oil, are you sure it wasn't coolant or ATF?

The top bolt of the tranny bolts you have shown in your pic above the starter. The heads have never been milled, they were new Dart Pro 1 aluminum 200cc heads, the short block was cleaned, and machined and assembled by a local machine shop that has been in the business for decades build everything from street motors to full out race engines. As for the intake gaskets, I do not use the end pieces on the china rail, just silicone and the dizzy gasket is dry as well as is the valve cover and back of intake. The bolt in question was wet with motor oil, no coolant, no tranny fluid. The car runs great, no oil burning, just this pesky leak, the motor only has problably 2000 miles on it and I am really puzzled by it. When I assembled the rest of the motor after getting the short block back, I checked the heads for straightness and flatness before assembling, the head gaskets are a multi layer type and I see no leaks from around head. I would like to get this resolved so that I can run my car down the 1/4 mile at Norwalk this summer to see how it does. Thanks for the replies, I haven't been online in few days and is why I haven't responded before this. Again, thanks.
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Old 04-26-2012, 06:16 PM
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Not sure why oil would be coming out of that bolt but if you're sure thats the place, you could clean the threads in the hole and on the bolt and apply a sealer to the bolt before you install it.
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Old 04-26-2012, 06:29 PM
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Quote:
Originally Posted by cc82z-28
The top bolt of the tranny bolts you have shown in your pic above the starter. The heads have never been milled, they were new Dart Pro 1 aluminum 200cc heads, the short block was cleaned, and machined and assembled by a local machine shop that has been in the business for decades build everything from street motors to full out race engines. As for the intake gaskets, I do not use the end pieces on the china rail, just silicone and the dizzy gasket is dry as well as is the valve cover and back of intake. The bolt in question was wet with motor oil, no coolant, no tranny fluid. The car runs great, no oil burning, just this pesky leak, the motor only has problably 2000 miles on it and I am really puzzled by it. When I assembled the rest of the motor after getting the short block back, I checked the heads for straightness and flatness before assembling, the head gaskets are a multi layer type and I see no leaks from around head. I would like to get this resolved so that I can run my car down the 1/4 mile at Norwalk this summer to see how it does. Thanks for the replies, I haven't been online in few days and is why I haven't responded before this. Again, thanks.
There are 4 plugs behind the flywheel on the back of the block. A large one closes the cam tunnel. The other 3 small ones each close an oil pressure passage main and two lifter feeds on each side of the valley. Any of those could leak.

Leaks from the china wall of either the front or back or the valley is also a common event. Whether gaskets or RTV or a mix of these materials, it remains a frequent source of oil. This is also sensitive to the RTV used, it certainly needs to be high temp automotive/aircraft rated not GE bath-tub stuff other wise it may not seal against either the effects of oil and fuel and/or fail from the heat. Even then it may not form a seal with the adjacent surface especially if a spot of oil or greasy finger print was left on the gasket surface of one part or another. I don't use RTV except for sparing amounts in problem areas like the corners where the china wall, head and intake manifold come together but my issue is having opened up too many other builders engines to find globs of the stuff in the valley and even in the pan.

Aluminum heads can also be the source it is not uncommon to have porosity of the casting which lets oil ooze through. While this is a greater problem with import heads nobody is immune.

If this is a two piece rear main seal block, this seal can be hard to make oil tight. The dribbles get picked up by the fly/flex when the engine is operating getting whipped around to come out from all sorts of places as well.

This is a pretty broad rage of possibilities, you'll have to clean everything and search with a bright light and keen eye, like that's news. Certainly going to the drags will add to your external oil collection when the high RPMs start resulting in the blow-by putting some pressure in the crankcase.


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