340 Rear Main Seal

After two months of detailing my drivetrain and getting the car back together , I found a small spot of oil on the ground under the car, I took off the bellhousing inspection cover and sure enough it is coming from the rear main seal. I decided I spent to much money and time to continue to have a leaker so I pulled the oil pan off tonight and I am not sure what to do. I used a super performace seal and only used RTV on the ends of the two short rubber pieces where they touch at the oil pan gasket. This oil leak was one of the reasons I pulled the engine out to begin with so I do not want this to continue. It appears that the oil is either going under or over the seal . I have less than an hour on this seal and I used Red Line assembly lube and I could see that coming out around the crank flange at the flywheel. I do not know what seal to purchase now to reassemble this engine with. I will now rotate a new seal slightly on reassembly, to help align the ends of the seal but i do not think that is where my leak was. I am leaning more towards a Diameter issue hard to check that in the car. I read about using a 318 magnum seal, which is supposed to be .010" bigger , but I do not know what brand to buy that in. So any help would be appreciated.

are those "side" seal pieces seating flush?

They are bottomed out into the groove of the cap, but are proud of the cap surface.They have a square shaped bottom and come to an angle at the top surface that is exposed. I assume that as the cap is tightened the rubber piece is crushed forming the seal of the cap to the block.But you may be on to something if the cap was not sitting flush at those rubber pieces, the main seal itself would not have a tight fit to the crank.

I ain't sure, more just thinking out loud than fact. You said it looked like it was coming thru (past) the seal or around it?

I think what I would do is do it over again (no choice really) & clean everything squeaky clean (which I know did) & likely a new pair of superformance seals. slightly polishing the knurl down a bit may help/be a good move. Did you say there was a slightly oversize seal available? I wondering is some nonhardening cement (a touch of permatex #2) on the ends where they meet as opposed to some hardening stuff would allow the seal to move slightly/conform a bit better to the round crank.

top half in backwards ?

I think you have the seal in backwards? Plus is that silicone you have on the seal ends?

I use rope seals and have no leaks.

That's not backwards, but it sure does not look like the thin seals mopar sells.

That is a Superperformance rear main seal. Silicone was only applied to the end of the two short rubber pieces where the oil pan gasket meets the main cap. No doubt I will be installing a new seal, but right now I just do not know which one to use. Yes I do think some polishing of the crank seal surface may help. I am hoping that Greg at Superperformance will chime in.

pretty sure Top Half is backwards. ? maybe not. carry on

Both are backwards, the angled "lip" points inside.

Look closer they are not backwards. they have a little lip at the back but the main angle is definitely toward the inside of the engine.there is a double lip on some small block seals.

Laugh if you want use High milege oil the oil will slow to stop in most cases

Why is the crank knurled on the sealing surface? That seems counterproductive.

Because when you use a rope seal, like original, it seals.

Ok I am interested in any solution , what brand rope seal do you recommend? Any secrets to their installation?

Thanks

I can't remember the last time I replaced a rope seal. Probably in 88. Not even sure if you can get them any more, but the knurled surface was used in conjunction with rope seals back when the factory used rope seals.

That little lip goes to the inside, but you do it the way you want. Let the drips begin.
The serrations are made to force the oil back into the engine no matter what type seal you use.

The small lip is just to keep the dirt out, you have it in the right way, lightly stone the flat mating surfaces on block and cap with a stone just to make sure its flat, use the seal thats one piece on the cap end and clean the ends of seal that meet with brake cleaner and add just a little rtv to all ends and put it together. Was it leaking out the back from just running in the driveway or driving down the road? My 340 had a suspect rear main leak that turned out to be the oil pan that I lived with till it got worse and finally decided to investigate more after 2 bolts rattled out. Weird thing is i put new ones where they fell out and retourqed them and ran it on lift, it still leaked but looked like it was leaking where the bolts screwed in so i removed them one at a time and cleaned each hole with brake cleaner and put some rtv around the inside of tbe washer and retightened them and have to say after owning the car for 20 yrs and 2 rebuilds it now doesnt leak a dtop anywhere. I just assumed after 2 rebuilds and it still leaking that there was something out of round where the seal installs plus the motor had a line bore at some time in its life, the wind from driving the car would blow the oil into the tourque convertor area then leak out after you park it for a while. Kind of reminds me of the guy looking for the bad lifter when his exhaust is leaking.

Well here's an idea for the OP, it's leaking now (twice) turn it around and see if it still leaks.

If you didn't put sealer in the groove the seal goes into that's probably where your leak is. On the ends of the seals you should use an adhesive sealer, not silicone. You'll never get a rope seal to slide into place with the crank shaft still bolted up tight. You need sealer on the side seals also, just a light coating in the channel and the mating surface.