Is there any way to PERMAMENTLY eliminate rear main oil leaks?

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cruiser

cruiser

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Hi Guys/Gals: Cruiser here. I've been enjoying driving my slant six 1974 Duster with its newly rebuilt engine. The motor runs very well, but I just cannot get rid of a persistent rear main oil leak. The shop that rebuilt the engine is very experienced and reputable. They installed a new rear main seal in November of 2024, which failed a month later. On Dec. 12th, they installed a new seal which is now leaking after about 1500 miles. So I'm looking at putting in my third rear main seal in about three months. So what's going on here? Does anyone out there own a slant six that DOESN'T leak oil out of the rear main? Does such an animal even exist? I could really use your advice, especially Slant Six Dan if you're out there. If you did cure your leaky seal, what product did you use and how did you install it. Is there some kind of super duper seal that I need to use this time? My expectation is for the engine to go 100,000 miles without leaking. Your thoughts? What worked for you? Am I nuts to expect the floor under my Duster to be clean and dry?

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Keep in mind, the Slant-6 (like most other engines of its day) was not well known for keeping the oil on the inside. They could've done a lot better job designing that oil pan gasket arrangement, for example. But no, the rear main seal will not necessarily leak.

The rear main seal halves have to be installed right way round, not inside-out. The halves of the seal should not be quite lined up with the halves of the metal where they sit (the split in the circle of the rear main seal should not align with the split in the circle of the rear main seal housing). There should be a small dab of suitably good RTV on the seal-half ends to seal the halves together, and another small dab on the corner pieces on the lower rear main seal housing.

ETA: I really like the look of that 1-piece seal RRR just posted. That has to be rightside-in, too, and I'd put the installation split at 12:00 with a small dab of RTV.
 
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They are a pain in the patootie to install, but the OEM factory "rope" seal works well. The newer type doesn't work as well as the original from the factory.
 
Is your mama yelling at you again? :lol: Next time say please and thank you.
 
Charrlie_S said:
They are a pain in the patootie to install, but the OEM factory "rope" seal works well. The newer type doesn't work as well as the original from the factory.
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Yes, but I've heard that the original style rope seals are no longer available. Whaddya think?
 
There's an easy way to stop the rear main from leaking permanently....

Drain the oil.... No oil = no leak...
 
Rope seal is still available.
Chrysler part number 2084411.
AMS Obsolete shows in stock.
Also many on eBay.
 
A properly designed modern Viton/Silicon seal has to go in the right way. It has a front & back. It is designed this way so that crankcase pressure [ blowby ] puts some force on the seal lip to seal it.

If the slant crank has a knurled seal area, I would have that machined down if using a Viton/Silicon seal.
 
Bewy said:
A properly designed modern Viton/Silicon seal has to go in the right way. It has a front & back. It is designed this way so that crankcase pressure [ blowby ] puts some force on the seal lip to seal it.

If the slant crank has a knurled seal area, I would have that machined down if using a Viton/Silicon seal.
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Yes I was wondering about the knurled area where the seal touches, that knurling is supposed to wind the oil back into the engine as the crank is turning.

Knurling works good with the rope seals because it is a wider sealing area.

The newer seals have a point of contact, and would seal better if the knurling was gone and the crank was smooth in that area.

Also sometimes the seals can wear a groove in the crank, like what happens to leaky torque converters.

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☆☆☆☆☆
 
cruiser said:
Yes, but I've heard that the original style rope seals are no longer available. Whaddya think?
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From what I understand, the original type rope seal is no longer available, and the "newer" ones are not as good a material. Something about asbestos being removed. You need to find some NOS seals. I have some of the old NOS seals in stock for my projects.
 
i used one of these

BOP 1 piece rear main seal got a 3 inch and cut it to size for my 2.5 inch seal diameter

BOP Engineering Engine Accessories
because the knurl on the crank that facilitates use of rope seal was worn away.

Process
cut seal. its got a metal core... solid in all but 1 place, which is marked. use a mini grinder hand tool with the thinnest cutting disk at highest rpm.

curve seal to nominally the right shape
cut off most of the excess
put in housing and slowly clamp down the beraing cap
when the cut ends of the seal lip pucker stop take it out trim a little bit off
continue until you can get housing on just at the point of the seal lip puckering
do 1 last tiny cut to get good ends

make sure you put it in the right way. check direction of the profile on the lip...will it drive oil back into the pan when the crank rotates? i think some of those pontiac/buick engines spin the wrong way, so work it out yourself.

put the join at the top.
glue it in like you would any other rubber seal



kinda worked
leaks with no PCV connected
doesn't seem to leak with PCV connected
I believe slant 6 is like my hemi 6. designed for rope seal
in which case there is go guarantee that the seal housing is truly concentric with the seal surface on the crank
a rope seal will conform to cover that issue
a rubber seal won't
i will say if you want to use rope you are better off with NOS ferguson tractor seal....
its the old asbestos rope, that worked.
Rather than that fibreglass like stuff with putty in the middle

you could also of course choose from a range of gland packing.

Graphite Gland Packing for sale | eBay

choose one where the inches/second of shaft rotation fits with RPM range and of course in a cross sectional area that is deeper than the depth of the V in the seal housing.
bash it into both halves using a nice round bar
cut a seal wide slot in an old credit card
put that around the end of the seal at each surface and use it as a depth gauge to cut the seal off cleanly with a credit cards worth standing proud
pull out seal
move it round slightly so it stick up at 1 side and is low at the other

daub ends with sealer
cover seal surface in lube
put cap on with offset ends of seal inter locking so the join is not at the parting line.
do not let the splayed ends of seal get into the parting line between cap and block, if you do the cap will sit cocked slightly fore or aft, removing any clearance on the close side and you will seize that bearing


gland packing.......you get 1 meter for half the cost of buying 2 pieces of exactly the same stuff in a baggy with a cardboard tag saying "slant 6 rope seal on it", that's some expensive bag and cardboard tag...

but of course this will only work properly with a well defined knurl on the crank
if its worn another solution is needed

Dave
 
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