59vetteman

As stated, the rear seal is leaking on my wife's 67 327 recently rebuilt engine. The rebuild shop pulled the pan and replaced the gasket and seal with a new one. Same result. The pan is the later style GM replacement, as the original was pretty banged up. The shop is using the cork and rubber type of gasket. The shop owner stated that the pan did not seem to put enough compression on the rear seal to form a proper bond. Has anyone else experienced this? I know there is a height difference in the replacement pan from the original at the timing cover location, but is there also a difference at the rear that would account for this. It does not leak at the timing cover, only at the rear seal. Thanks for any suggestions. Al

Robert61

Are you sure its the seal, not a rear plug, cam plug, intake, or sending unit. Just asking. Several years ago I built a motlor for a friend in a race car. He kept saying the rear main was pouring. After 2 weekends they were starting to pull the engine when they noticed no one had tightened the oil pressure line. The lip seal is the same on the old and new. There is always the potential for leaks down each side of the main cap. I have seen instances where the lip of the main seal didn't touch the crank.



I did run into this on a 4.3 v6. The pan wasn't touching the rubber on the rear cap. I went to a different gasket. As far as I remember the only difference in sbc pans is the thicker front seal. I don't think there's a differrence from a small journal 327 to a large journal. If he was using a late style pan the dip stick is on the wrong side.

LB66383

The pan no effect on the rear main seal. The seal is captive in the rear main bearing cap and the block. Having a bad oil pan gasket will cause a leak there, but has nothing to do with the rear main seal.

Robert61

The rebuild shop should have stock Chevy pans. If they remove your pan again tell them to put the pan on a flat surface and measure from the surface to the radius where the pan contacts the seal. Then do the same with a known stock Chevy pan.

Westlotorn

The engine is new and should be very clean. In a dark room you can shine a black light on your block and search for the leak path. New clean oil will glow in the purple light.
This will hopefully help spot an area where oil is running down.
The intake manifold china wall seal is always a suspect. If you have a leak at the rear china wall it will show up in the same place as a rear main seal leak.

tbarb

Another leak point is the factory steel valve covers in the rear lower corners, they never seal good at that point and oil will puddle there. That leak will also show up lower where the pan radius is located.

59vetteman

They checked the oil galley plugs, oil pressure fitting and line, valve covers, and the intake to block seal. All these areas were dry. I, too had looked with a light and mirror and felt with fingers at the VC , oil line, vent tube, and retightened all intake, VC and oil pan bolts. As previously stated, the shop owner says it appears to be coming from the rear main and that there doesn't seem to be enough pressure exerted on the seal for it to seal properly. Just wondering if anyone else had run into this? If it is a inferior seal made "over yonder" or what?

Robert61

Yes I have run into the rear seal not touching the crank. For some reason I thought you were referring to to pan seal not getting enough pressure. When they install the crank he should be looking at the seal to make sure there is good contact on both sides that you can see with no cap on. The one I ran into the seal was off to one side. It didn't touch the crank on one side at all. After one time I pay very close attention there from then on. I made a shim out of a beer can while the owner of the engine watched. I glued it in with ultra black Permatex. No more leak and he was happy. When I say I made a shim I cut the aluminum the width of the a lot in the seal. In the 70s and 80s when you aligned bored a 400 Chevy you had to bore out where the rear main seal goes as well. The 400 uses the same seal as a 350. But the main bearing bore is larger than the seal area so you had to open everything up to one size. To remedy the problem then we used a wire tie because it was the correct width and thickness to fill the gap. Later Fel Pro came out with a special seal just for this.



If you do decide to shim it use the Permatex on both sides of the shim. Many will say you don't need sealant on the rear main seal. I never install one without it.

65tripleblack

If the crank is grooved, he can use an offset rear main seal.

dmaxx3500

I think they make a ''speedy sleeve'' for that too