Rear Main Seal Help

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Apr 9, 2005 | 08:25 AM

LD85

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From: Indianapolis IN

Rear Main Seal Help

I have a 400 SBC crank that has been ground down .020"

Does this cause a problem with the stock 400 crank rear main seal?
Is there an under size seal that should be used?

I have taken my oil pan off and put it back on 3-4 times and every time I get a leak once the oil starts to get warm. I am guessing that the rear main seal is not sealing.

I put the anaerobic sealer on the crank main cap this time so I am really confident that this is not it, and I offset the rear main seal halves @ ¼” in the cap.

Apr 9, 2005 | 01:02 PM

CFI-EFI

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From: The Top of Utah

The seal rides on the area of the crank behind the oil flinger. That surface shouldn't have been touched when the mains were ground.

RACE ON!!!

Apr 9, 2005 | 03:17 PM

cardo0

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From: Las Vegas - Just stop perpetuating myths please.

Couple more details.

Quote:

Originally Posted by LD85

I have a 400 SBC crank that has been ground down .020"
Does this cause a problem with the stock 400 crank rear main seal?
Is there an under size seal that should be used? I have taken my oil pan off and put it back on 3-4 times and every time I get a leak once the oil starts to get warm. I am guessing that the rear main seal is not sealing. I put the anaerobic sealer on the crank main cap this time so I am really confident that this is not it, and I offset the rear main seal halves @ ¼” in the cap.

Now u still need to use some sealer (Permetex #2) where the rear seal 2 halfs meet eventhough offset 1/4". Not much but some.
Also this is bit opposite from sealing but u need to wet the seal with oil before start-up so the seal doesn't rub on dry crank.
Just take ur time and care as the rear seal ends that meet need to be dry for the sealer to adhere but the rest of the seal needs a little oil for start-up.
Also be careful not to use too much sealer on the main cap such that it won't set correctly. And let it (sealer) set-up for a couple days berfore start-up.

Other than these ideas if ur still leaking oil it maybe a crankcase pressure issue and ur PCV is not working to remove blow-by. Meaning u have positive crankcase pressure at hi-rpm rather than negative/vacuum in the crankcase - this happens often on the forum.
Good luck. cardo0

Apr 9, 2005 | 04:22 PM

LD85

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From: Indianapolis IN

Thanks guys, I have put this pan on 3-4 times and it leaks every time no matter what I try. I fear it is the main seal because it drips a fast drip down the bottom lip of the oil pan.

I put the anaerobic sealer on the main cap and thought this would do it but I have not checked the pressure issue, will do that today.

Apr 11, 2005 | 11:25 AM

LD85

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From: Indianapolis IN

UPDATE: First, I called my short block builder, they said that IF the crank was align honed, (which it was) then the rear main seal has to be oversized on the rear main OD . He said that when they hone the main caps, the ID of the main cap becomes larger and the rear main seal OD is then too small. He said to use a Felpro 2909. He said to look at the cross hatch marks in the cap and if they are there, then it was for sure honed.

I wil ltry to do some measuring when I take the pan back off, again!

Apr 11, 2005 | 01:25 PM

MotorHead

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From: Who says "Nothing is impossible" ? I've been doing nothing for years.

Yes you need that Felpro seal in there if it align honed, I put it in mine

Apr 11, 2005 | 07:42 PM

LD85

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From: Indianapolis IN

Quote:

Originally Posted by MotorHead

Yes you need that Felpro seal in there if it align honed, I put it in mine

Motorhead, where were you 3 oil pand gaskets ago!

Just kidding,,, you are right, the problem was the seal, I pulled the pan this evening and I have a sloppy stock rear main seal and need the FP-2909.

What a relief, this was getting to be depressing!

Thanks for the input guys!

Apr 11, 2005 | 07:55 PM

bob

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From: Gabriola BC

thanks for that tip--It is not on my corvette but I have a weepie rear main seal on a 350 that was align honed and didn't know about that seal. Thanks again
bob