Rear main seal leak and need advice

[Stumper]

Just a thought.
Could crank case pressure be causing many of the rear main leaks ?
I see quite a few engines running no pcv valve .
Just a breather set up.
Some years back I tried running a 383 with a breather only in each valve cover . Never could get that engine sealed up until I switched to pcv valve on one side and breather on the other.

This is a good point, especially with the highly modded engines.

 

[68 HEMI GTS]

I’ve only been using the black felpro rubber seals with stock retainers lately. Even on my high hp stuff. I also take the stock retainer and hit it on some 220 grit W/D with wd40 and lap a little material off the face. It’s worked well. I haven’t had that much luck with the fancy after market retainers.

 

[dvw]

If the seal retainer sets to one side, the upper a lower halves of the seal may not align. Easy to check with the crank not installed. Easy fix. Drill the retainer holes slightly oversize. The seal halves won't be forced off center by the retainer bolts. Sometimes the seal retainer opening isn't centered in the block. That's a good reason to use RTV in place of the side seals.
Doug

 

[1STMP]

Just a thought.
Could crank case pressure be causing many of the rear main leaks ?
I see quite a few engines running no pcv valve .
Just a breather set up.
Some years back I tried running a 383 with a breather only in each valve cover . Never could get that engine sealed up until I switched to pcv valve on one side and breather on the other.

Definitely one for the debate stage. Before PCV
valves existed (1967 back), did all engines suffer
rear main seal leaks from crank case pressures?
I'm inclined to believe they had about the same
failure rate back then. My vote is wear on the
sealing surface. Just a few thousands wear is
enough (with added crank case pressures) to blow
oil past the seal. Of course, installation methods
contribute. Most here start with rebuilding
engines pulled from salvage yards, or cars that
have sat for possibly many years. How well were
those engine maintained before we got s hold of
them? Very few are original owners who were
OCD with maintenance. Just my .02....

 

[BSB67]

The question remains.
If the leak stops and just the residual drips when you are parked, is that a crankcase pressure issue only?
OR
If the Oil continues to drip alot when parked over time, would that be a better example of a rear main seal issue?

No.
The rear main seal will not leak when parked because the oil level is below the seal

 

[1968rt]

From my experience the rubber seal and a knurled crankshaft = a leak. Last few motors I built I had the machine shop polish off the knurling. Used a rubber Felpro seal and no leaks.

 

[Ray70Chrg]

From my experience the rubber seal and a knurled crankshaft = a leak. Last few motors I built I had the machine shop polish off the knurling. Used a rubber Felpro seal and no leaks.

1968rt, that's a very interesting point you make about the knurled area. I know the lip of the seal is not supposed to be on the knurled surface but unless you have the engine out you can not be sure that this is happening. The front seal, in contrast, doesn't have this problem but of course the design there is different. When crankshafts are replaced, do all of them have the knurled area? If the answer is no, do the non knurled crankshafts rear seals perform better. I know there are several professional engine builders on this site so maybe some of them can respond.

 

[Potts]

This is where I stand, hope it helps someone.
I had my 69 383 rebuilt professionally where I used to live.
The guy preferred rope seals.
Engine leaked. At the time, He was 4 hours away so we talked about the leaks and even thought it was from the valve cover. After ruling out VC, found out it was the Rear main, slinging oil to the right side and exhaust manifold.
Fast forward, found another guy willing to replace the seal without pulling the engine. Dropped oil pan and cap.
He dial calipered the knurled area, was smooth with no signs of change. Installed Vitton Rubber seal, it still leaked.
Went back and tried Vitton Rubber with Billet cap.
It still leaks. Frustrated, but not giving up, going on 3 years.
Now I have a local Mopar guy, close to where I moved, interested to take a look at it soon.
Hoping for better results.

 

[Potts]

How about this one?
Forgot where I heard it, but tell me this aint a long shot.
If someone is unfortunately using a Chrysler Marine engine crank, it is possible that the knurled area is actually drawing oil out of the engine since those crankshafts were built to rotate opposite and the knurled area was machined opposite. I want to call Shenanigans on that folklore.

Where does it end.

 

[AR67GTX]

Please note - I understand that oil stop leaks have a snake oil reputation. And in full disclosure I have not had the nerve to try this stuff yet - but I do have a couple bottles sitting on my shelf. I have a 66 Corvette and frequent the Corvette Forums and there have been many, many positive reports coming in from even usually skeptical members and mechanics, about this BlueDevil product really working at drying up oil leaks without any evil consequences. My 66 Hemi is dripping everywhere and it’s going to be awhile before I can get to replacing gaskets, so I’m planning to put this in it shortly in hope of slowing down some of the leaks in the meantime.

So, not advocating but just throwing it out there for thought.

https://www.amazon.com/BlueDevil-Products-49499-Stop-Leak/dp/B000OAEN7C/ref=asc_df_B000OAEN7C/?tag=hyprod-20&linkCode=df0&hvadid=312141533517&hvpos=&hvnetw=g&hvrand=7601430947039249356&hvpone=&hvptwo=&hvqmt=&hvdev=c&hvdvcmdl=&hvlocint=&hvlocphy=9025810&hvtargid=pla-569800665003&psc=1&tag=&ref=&adgrpid=61941536837&hvpone=&hvptwo=&hvadid=312141533517&hvpos=&hvnetw=g&hvrand=7601430947039249356&hvqmt=&hvdev=c&hvdvcmdl=&hvlocint=&hvlocphy=9025810&hvtargid=pla-569800665003

 

[Lexi]

Please note - I understand that oil stop leaks have a snake oil reputation. And in full disclosure I have not had the nerve to try this stuff yet - but I do have a couple bottles sitting on my shelf. I have a 66 Corvette and frequent the Corvette Forums and there have been many, many positive reports coming in from even usually skeptical members and mechanics, about this BlueDevil product really working at drying up oil leaks without any evil consequences. My 66 Hemi is dripping everywhere and it’s going to be awhile before I can get to replacing gaskets, so I’m planning to put this in it shortly in hope of slowing down some of the leaks in the meantime.

So, not advocating but just throwing it out there for thought.
https://www.amazon.com/BlueDevil-Pr...t=&hvlocphy=9025810&hvtargid=pla-569800665003
https://www.amazon.com/BlueDevil-Pr...t=&hvlocphy=9025810&hvtargid=pla-569800665003

I would appreciate it if you can post an update with results, once you give this a try. Thanks

 

[Potts]

I hear ya, but for me, kinda hard to pour a stop leak into a fresh build.
Let us know how it works for you.

 

[68 HEMI GTS]

From my experience the rubber seal and a knurled crankshaft = a leak. Last few motors I built I had the machine shop polish off the knurling. Used a rubber Felpro seal and no leaks.

The knurling on a crank doesn’t bother anything long as it’s going the right direction. Machining it off and reducing the diameter sure could though.

 

[1STMP]

Be careful with that Blue Devil stuff. It eats paint
and some plastics almost as bad as brake fluid.

 

[AR67GTX]

I’ll follow up when I can. The car is still somewhat apart and waiting for parts being plated. It will be a good test as it drips everywhere.

 

[BSB67]

After ruling out VC, found out it was the Rear main, slinging oil to the right side and exhaust manifold.

Hmmmmm. I wonder how a rear main leak would sling oil any where other than in the bell housing. If it’s on you exhaust manifold, it probably is VC.

 

[Potts]

No.
Addressed the VC in great detail.
Maybe sling isn't the correct term.
Oil runs out from the clutch area and burns up on the right side exhaust.
Thinking it Prob gets pulled over that way while driving.

 

[Beekeeper]

So I did find some things on this whole rear main seal leak ordeal some from reading and some from looking and checking my own engine. First thing I see most while reading is these fancy billet retainers are not the best route to go in most cases mainly for the fact there is not any room to speak of between the main cap and retainer to allow oil drain back. So I see Mancini’s new retainer addresses this by milling out some material like the factory retainer was and here’s something I found on my own big block engine. After tearing this thing back down to the bare block I installed the #5 main cap and torqued it down and find that in order for the seal ends to line up correctly the retainer is against the #5 cap.That makes the alignment of the seal ends easy to locate but here is something very interesting I found keep in mind this is a factory block with its original main caps. I put the factory retainer against the #5 cap and slide it down into place over the seal but it did not seat correctly because one of the bumps where the pan bolt holes are is hitting the main cap.I know your like impossible! But I assure you it hits I have two factory retainers and both had interference with the #5 cap in the same spot. I’ve read numerous threads here and elsewhere where someone was on #2 3 or 4 seal and still leaks
so I say all this to say check that there is no interference whatsoever between any retainer and the #5 cap or you will have a leak now or at some point. Offset the ends or the seals or clock them at 6 and twelve or whatever you feel you need to do to be successful but if there’s interference with the retainer and cap you either get lucky or it will leak. I will post some pics of what I found on my engine as soon as I get back to the shop to take the pics and do my best to make of video to help explain what I found.

 

[Fran Blacker]

I've posted a few times (not lately) that's a problem when guys have leaking rear main seal. A friend worked at Secord Chrysler Plymouth rebuilt a motor and had rear main leak because of pan bolt bumps. He helped me assemble my first Hemi and told me about that. Glad you found and fixed it.

 

[Potts]

I have a persistent rear main BB leak.
Please post a pic or something.
Desperate.
Thanks
Potts