Hot Rods Rear Main 1st Gen 392 Hemi

Been here before with this topic. I'm baaaaack.
Just replaced rear main seal "again" on my 1st Gen 392 Chrysler Hemi. Immediately started to leak, and I am 99.44 % sure I did it correctly.
What else could be causing it to leak if the seal is good and correctly installed. Any ideas and suggestions solicited and greatly appreciated.
Jack

 

There is a thread in hemi tech index on rear main seals for 392 hemi. Make sure you get your seals from hotheads they have the correct parts rope or neopreme.

 

rear main seal thread

Technical - 392 Hemi rear main replacement | The H.A.M.B. (jalopyjournal.com)

 

Hot heads has it,,,,,I think they are the only one that is correct for 392 .
Did you purchase your seal from them ?

Tommy

 

Best gaskets has rope seal but, it is questionable at sealing the crank due to the material used. None of the 'good stuff' is allowed these days. Current rope is a far cry from the good-ol-days.
If you scour swap meets you may find some old rope for some other application. Generally, the cross section will be similar so you only need enough length.
Sometime back I sourced a manufacture that would make a one-piece rubber seal but I found little support for the project and at my age I was/am not interested in adding inventory.
If anyone with reasonable finances wants to take on that project I'll hook you up with the mfgr. Give me a call.

Hot Rods - 392 HEMI rear main seal | The H.A.M.B. (jalopyjournal.com)

 

Sorry Gary,,,,,I wasn’t trying to leave you out .
I assumed you had never pursued your plan for the seal,,,,because of the amount of capital involved and the potential return on investment.
Also,,,,your retirement plans,,,,age .
Sorry .

Tommy

 

Hi Tommy, no worries. I certainly don't feel left out of anything unless I choose it! I would like to do other stuff before I check out....

 

Yes.
When I talked to Eric at Hot Heads, he said apparently crank had been turned would be only reason seal would leak. Eric said probably needed shims, which came with the seal. They did not help. Anyone have any ideas what would be a good material I could use to make thicker shims than the ones that came with the seal?

 

Good question,,,I can’t help at all .
Maybe like Gary suggested,,,if you could find some good old style rope seal material and leave it a little extra long when installing ?
I can’t imagine a crank seal area being cut down that much,,,,unless,,,,it had been severely damaged.
Some 392 cranks have seen a lot of severe service,,,,,,,you never know what has been done to them .

Would it be possible to add some shim material in the cavity in the block and cap like Eric suggested ?
If he suggested it,,,I would definitely try it ?
What was the shim thickness ?

Tommy

 

First of all, in this group you don't need to say "1st Gen 392 Chrysler Hemi". If you simply say 392 Hemi we'll all know what you're referring to.

Second, and it's a long shot, but I don't recall if the hemis had angled knurling on the crankshaft seal area. If they do and it's a reverse rotation marine crank the knurling could be your issue, as it would push oil out the seal.

 

All rope seals will drip a little... I have one in mine and when I install them I leave them a little long and use a brass punch to pack them.... I have had better luck with rope seals over the years than two piece neoprene ones....

 

Built my '52 331 hemi 30 years ago using the good old rope seal that came in my JC Whitney gasket kit. Still sealing good. As I recall the seal area had tiny diagonl grooves scratched in it to 'pump' oil bak to the sump as the engine turned. Does yours have those scratches? Regardless, the rope has plenty of crush so should seal on a mildly turned surface.I'm guessing it is a material problem like the other comments.

See here
https://www.jalopyjournal.com/forum/threads/hemi-crankshaft-rear-main-seal-surface.85173/

 

This may be way off, but are you 100% sure it's the seal? I have seen cam plugs leak and look like a rear seal leaking. Just a thought.

 

As noted, the diagonal knurl is a critical component. If it has been removed then the rope, any rope, will leak.
If removed, then you are stuck with neoprene. Conversely, if the knurl is intact it will destroy a lip seal. The problem with current lip seals is that the block was not designed for them so the available seals are only 'close'. This is why I started the split seal project that would have a seal designed for the exact groove in the block/cap.

 

When you align hone a 400 SBC, you have to cut the lip down that the rear seal fits into. A special thicker seal is available to compensate or you could cut some thin strips from aluminum sheet that is the same thickness as the cut you took out of the block. I doubt the early Hemi's had that same procedure when align honing, but you could try something like that. As has been said, it'll be tough to seal if the knurl is gone.

 

All three that I have in the shop right now have those tiny grooves.

I wonder what would be a plausible means to recreate them, or even how they were put there at the factory.

 

I have found that excessive oil clearance on the mains will contribute to oil leakage at the rear seal. For a street engine I would try for .002" clearance. Greg

 

A lot of cranks have a flange between the rear main and the seal to prevent direct oil pressure spray from blowing past the rear seal. A lot of engines also had tin shields that fit on the crank snout between the lower timing gear and harmonic balancer to also prevent oil spray from the front main from doing the same.

 

A machine shop might be able to knurl them. Would take a shop with knowhow for sure.

 

No, not sure, but I believe it to be thes seal. The valve cover (PS) was leaking. I installed new gasket, still have "a" leak.
Was considering gasket material to make a shim?
I'm on a tight budget, so last resort is removing the engine and having machine work done.
Jack

 

...and the correct tooling....

 

Thanks for everyones advice. Always know I can count on you guys.

Going have to put it on hold, but I am going out on a limb and make a shim out of gasket material. Hell, what could go wrong ?? .
Going to put the ole DeSoto (Odd rOd) in body shop to make some touch up body work. If lucky, will have it back by the end of March, then back to the rear main.

Again, Thanks
Jack

 

Is this normally aspirated or supercharged? Is the crankcase venting properly? Does the seal surface mic out at the low end of the specs?

 

My racing GMC’s always leaked. Added a vacuum pump. My Y-block did the same with a Best seal and spacer sides properly installed. Added a PVC system with has 1.5” of vacuum at idle and problem is all but gone. It can drip but it’s next to nothing and I can definitely live with it.

 

What about cam plug or oil galley plugs in the back of the block?

 

Normally aspirated, 2 500cfm Edelbrock carbs.

 

Strange things can happen if the crankcase isn't properly vented. Blow-by can pressurize the c/case. Thermal expansion occurs as the oil, coolant and the engine in general come up to operating temperature creating more pressure. And then there's turbulence created by the crank spinning around and the pistons displacing air as they travel up and down their bores.

If enough pressure builds up it will try to find a way to escape. It will push its way past the front and rear crank seals, pan gasket, v/c gaskets, dipstick tube, oil fill cap, anywhere it can find and take some oil with it. And this happens when the breather, road draft tube or PCV system are plugged or otherwise restricted.

A working draft tube system is better than nothing. But switching over to a PCV system as Jimmy Six mentions above is even better. In a racing application a separate vacuum pump might be required, though for a street driven engine you can get the same results using the engine's manifold vacuum. And as an added bonus it will help keep your oil cleaner by drawing out moisture and unburned fuel vapors by running the c/case under a slight vacuum.

You may in fact have a defective seal, but a poorly vented engine will only make matters worse.

 

I do have PCV from breather on the valve cover to port on the back carb. Educate me, what is proper PCV syatem?
I am running an 8 quart baffled oil pan.

Jack

 

How does fresh filtered air get into the crank case?

 

Don't know what you mean??
How does "fresh filtered" air get into any crank case?

I am considering running the hose from the PCV to rear and bottom of the engine. Is that a viable option?
I saw an article in Good Guys Gazette about a PC Valve that has adjustments to regulate the function of the PCV?