Differences in LA versus Big Block rear main oil seals

[Kern Dog]

I rebuilt the 440-493 and installed a rear main from my stash of parts. It fit so I stupidly assumed that it was correct. I just started it and have a leak. Fine droplets are flinging off the back of the engine and it looks like it is coming from the crank, not the side seals of the retainer.
These are two matching sets. One came directly from a new gasket set for a 440.

Here is another one with a different part number that looks similar.

Finally, there is this one that looks like one spec'd for LA series engines according to images on Rock Auto and Summit Racing sites.

None of the numbers on these bags matches anything online that I have checked.
The seal that I used was a MOPAR brand seal but again, I wonder if it was for a LA series and had some slight difference that I couldn't see.
Anyone have any insight on this?

 

[Kern Dog]

With a little digging, I found out the following.....
The rear seal surface on the 440 is approximately 2.81 as shown on these Chinese digital calipers......

A 318 crank I had was smaller.....

Here was a weird discovery....the final one was a 360.

Whuuut?

My situation could be the following:

* Correct 440 seal in right but not sealing well.
* Correct 440 seal in wrong, the half in block is in right, the half in the retainer is in backwards.
* Incorrect 318 seal too small, leaving a gap for oil to leak out.
* Incorrect 360 seal too big, distorted when the retainer was tightened down, leaving gaps for oi to leak out.
Oddly, the 360 crank main journal is stepped up in size at the oil seal area. Why???

 

[66 Sat]

With a little digging, I found out the following.....
The rear seal surface on the 440 is approximately 2.81 as shown on these Chinese digital calipers......

View attachment 1366185View attachment 1366186

A 318 crank I had was smaller.....

View attachment 1366187View attachment 1366188

Here was a weird discovery....the final one was a 360.

View attachment 1366189View attachment 1366191

Whuuut?

My situation could be the following:

* Correct 440 seal in right but not sealing well.
* Correct 440 seal in wrong, the half in block is in right, the half in the retainer is in backwards.
* Incorrect 318 seal too small, leaving a gap for oil to leak out.
* Incorrect 360 seal too big, distorted when the retainer was tightened down, leaving gaps for oi to leak out.
Oddly, the 360 crank main journal is stepped up in size at the oil seal area. Why???

This sucks the big one...especially if you have to pull the engine to fix it.
I have a minor oil leak in my poly stroker I put back in a few weeks ago. I think it's coming from the oil filter plate and not the rear main, but I may have to remove the engine in the future if it is the rear main. I'm just not going to do it yet - maybe in a few weeks once I've got the mental resolve to do it all again.
I love working on old cars, but sometimes they really try my patience.

 

[kiwigtx]

I thought there would be a big difference between them Greg. This is the rear main seal of the 360 that my A100 arrived with......some doofus managed to mangle the installation. It amazingly didn't leak though.....how, I do not know.

 

[Kern Dog]

The engine stays in place. The upper half gets pushed out and another half gets pressed in.
When I built my first 440 in 2001, I had a leak from the back of the block. I replaced the rear main seal halves this way. That time, it turned out to be gallery plugs that were not tight enough.

 

[Kern Dog]

I thought there would be a big difference between them Greg. This is the rear main seal of the 360 that my A100 arrived with......some doofus managed to mangle the installation. It amazingly didn't leak though.....how, I do not know.

View attachment 1366231

I think that is the rear seal for the oil pan, not the one between the crank and the #5 main cap.
That is an ugly "fit" though.

 

[kiwigtx]

I think that is the rear seal for the oil pan, not the one between the crank and the #5 main cap.
That is an ugly "fit" though.

Yes, that is the pan seal.....and yes it is very ugly.

 

[multimopes]

Just a shot in the dark, but would you consider trying an oil additive. There is a product named "Seal Lube" that I have witnessed miracles from. It does not change the viscosity or lubricating properties of your oil. It simply expands the gasket material itself. I have seen a guy with a bad leak on a power steering box that was literally running out, not just dripping. It stopped it completely. I have used it several times myself and as a result, I keep a bottle in my stash for any surprises that may arise. Good luck!