1967 GTX 440 rear main leaking

[Mopar Rookie]

Hello
I am working on a 1967 GTX with a 440 complete with a rear main leak. I have been unable to correct this issue. Previous owner replaced the stock seal retainer with a billet seal retainer from Mancini Racing, and new rear main seals while the engine was out of the car. I purchased the car and completed putting the engine back together (it was in the car needed parts belts, radiator etc to be reinstalled) Fired up the car “sounds great”, but after 5 min at idle left an oil spot about the size of 2”-3” diameter. :-(
I pulled the oil Pan, I then replaced the Mancini Racing seal retainer with new retainer billet seal retainer from 440 Source (list below)
200-1031 Rear Main Seal Cap - Billet Aluminum
109-1501 Rear Seal Cap Bolts - Set of 2 New
144-1000 Viton Rear Seal
144-1001 Silicone Rear Seal End Strips Kit

I am not able to physically pull the engine to try this with engine out of the car, looking for suggestions from anybody that has had work on their big block from a shop that they had good experience with. Or any suggestions on what to do while the engine is in the car. I am in the Sacramento area and looking for a shop with mechanic with better skills than me to fix my rear main leak.
Thanks for the read and any suggestions
Tim

 

[AR67GTX]

Are you really sure it’s not coming down from the rear corners of the valve covers or oil pressure sending unit or rear of valley cover? If not I would peek inside the bellhousing and if the inside is wet that would be consistent with the rear crank seal and oil being flung around off the crank flange. If the inside looks dry but it’s oily on the oil pan flange and bottom of seal retainer and block, that would be consistent with the retainer side seals leaking. IMO. Good luck.

 

[QuickBpBp]

Since multiple rear main seals were done it could be a rear oil galley plug in the back of the block that's leaking...

 

[AR67GTX]

True - I accidentally knocked the rear cam plug loose on a Pontiac doing a cam change and guess I was too rough with it. Undercoated the rear the floor pans of the car on the first drive.

 

[PurpleBeeper]

You can do it with the engine in the car. I've been fighting a rear main seal leak myself.
1. Knock center link of steering loose from the pitman arm & idler arm so the center link hangs down
2. Drain oil & remove pan
3. Remove rear main seal "cap"

The "tricks" I've learned are
a. the special rear main seal caps are supposed to help
b. Offset the ends of the rear main seal halves aren't right at the parting line where the rear main seal cap meets the block....basically, don't line up the seal gap with the rear main seal cap & block gap
c. Use a drop of glue (type? can't remember) on the ends of the main seal halves so they're glued together

 

[DanielSlocum]

offsetting the seal ends aprox 1/8 inch will virtually guarantee that the seal lips line up on the two halves. i would mill or file .005-.010 off the seal retainers mating surface [to the block] which will compress the seal a bit more. that has worked for me in the past when i had a leaker. good luck.

 

[Geoff 2]

What I have found:
I compared the aftermarket seal retainer with the factory retainer & the a/market one has the seal groove deeper. From memory, about 0.025". That means less crush on the seal.

I have had failures with the brown coloured seals. In one engine, the seal edge just disintegrated into small bits, was well lubed with grease at install. Faulty batch/material? Don't know, but a black two piece seal fixed the leak.

 

[JackpotJim]

I finally solved a rear main seal leak in my 512 after close to 1 years of replacing seals and main seal caps. I found that with my Milodon 7 quart pan if I went by my aftermarket dip stick I had close to a quart too much oil in the pan. After changing oil I measured close to 8 quarts drained from the pan. I'm now running the engine showing a quart low on the dip stick and my leak is gone. Yes, I've seen the arguments on oil pan capacity in relationship to the full mark on the dip stick. I'm comfortable running the engine on 7.5 quarts with filter change even though my dip stick shows a quart low.

 

[MCODECUDA]

True - I accidentally knocked the rear cam plug loose on a Pontiac doing a cam change and guess I was too rough with it. Undercoated the rear the floor pans of the car on the first drive.

I had a similar issue with my Belvedere. I could not stop it from leaking. After changing motors I noticed oil leaking from the rear cam plug. I just put silicone on it but I plan on priming the oil pump on the engine stand just to see if that fixes the problem. I know that it wasn’t spewing out of the plug so I’ll see if that does the trick.

 

[Mopar Miki]

remove the seal retainer
apply a light coating of grease to the exposed crank surface
rotate engine and verify upper seal is leaving a solid signature mark in the grease

reapply the light coating of grease, install a pair of studs & push the bearing retainer/seal into place; verify lower seal is leaving a solid signature mark in the grease.

all good? the problem is with the side seals
if not post pics

 

[lewtot184]

All of my rear main leaks were the valve cover back corner,...lol!