Rear main seal leaking

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brodphish

brodphish

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I have a 340 punched to 417 attached to a 727. It appears they is a small leak at the main seal when the engine is running. To correct this does the engine need to come all the way out? Or can it be loosed / unbolted and pulled forward a bit to access and change the real seal? I assume the answer would have a major impact on the cost involved.
 
Never heard of one having to come all the way out. Never done one myself, always had mechanic do it on several of my smallblock 360's. I know he's loosened motor mounts to move engine up some. I guess it also depends on what oil pan you have too.
 
it can be done in the car but first make sure your 100% sure its the seal . first check the valve covers oil sending unit and the back of the intake manifold for leaks .wipe everything down good first .
 
Also make sure you have proper crank case ventilation, The system needs to breath, not pressure up.
 
The center link and tie rods from side to side need to come out and the motor lifted and blocked between the motor mounts and K as high as it allows.
Then the pan can come off and the seal replaced.
I have done it a couple of times on different cars.

Don't forget to remove the distributor cap first so it doesn't get jammed against the firewall and broken.
 
Also, pay close attention to what way you orient the seal. The lip of the seal should face the engine...not the transmission. That seems backwards but it isn't. I think a lot of SB rear main leaks are caused by the seal being installed backwards. My Challenger rear main is leaking. My guess is that I installed it incorrectly. Not very enthused about pulling it apart.
 
burdar said:
Also, pay close attention to what way you orient the seal. The lip of the seal should face the engine...not the transmission. That seems backwards but it isn't. I think a lot of SB rear main leaks are caused by the seal being installed backwards. My Challenger rear main is leaking. My guess is that I installed it incorrectly. Not very enthused about pulling it apart.
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if u ain`t got a pcv system, try that first .
 
Mines a stock restored car, so all the factory PCV system is in place. It started leaking right from the first start-up.

I've also read where oil can leak between the main cap and block if both aren't completely flat. Some people even recommend a little RTV on the ends of the seals where they butt together.
 
burdar said:
Mines a stock restored car, so all the factory PCV system is in place. It started leaking right from the first start-up.

I've also read where oil can leak between the main cap and block if both aren't completely flat. Some people even recommend a little RTV on the ends of the seals where they butt together.
Click to expand...

I ALWAYS put just a little tiny dab where the seals come together as well as slightly clocking the seal AND a film from the edges of the seal all the way across between the main cap and block.
Like this but with the seal slightly rotated so one end sticks up about 1/4 inch and the other side sunk down about 1/4.
Slightly rotating the seal keeps the seal seams from matching up with the cap to block seams possibly allowing a leak.
Also on the inboard side of any pan bolt holes, unlike the way I marked the top of the cap. :D

seal.jpg
 
If the leak is indeed small, just make a bracket that holds a baby diaper and drive it until a good reason for engine removal arises.
 
Logan said:
If the leak is indeed small, just make a bracket that holds a baby diaper and drive it until a good reason for engine removal arises.
Click to expand...

This is what I did except I just let it leak on the ground. Very irritating but that's what I did. I had to pull the engine recently because I changed to a rear sump pan and there was no way to seal the back of the pan easily. Keep in mind this engine already had the rear main replaced twice with the Fel-Pro single lip seal. This time I used Superformance double lip seal from Mancini along with Right Stuff sealant. I coated the cap surface with a VERY thin coat of sealer, like you can see through it thin. I did a very small dab on the ends of the seals and 3 rear mains seals later in 700 miles of use, the Superformance seal did the trick. This is the first time I haven't seen this engine seep from the rear main. I will not use the single lip Fel-Pro seal ever again and I'll recommend anyone to not use them. I know guys use them with no leaks, but after my experience, no way. Never again. I had a thread on it here: 340 Rear Main Seal Install with Superformance Seal?
 
I finally had some time to look into this further. My favorite local speed shop has an old-timer whose replaced a lot of Mopar big - block main seals, they said it would be 1 -2 days of labor. That seems expensive to fix what is just an irritation. I would likely do it but it seems the issue may arise again if not done exactly right with the right parts (ands that does not seem clear).

Maybe I'll go the baby diaper route. But it's starting to make me a little crazy.
 
Ya...think I to got replace the rear main on my 340 as well. Started small, just a few drips after driving it....now slinging oil from the flywheel inspection cover, especially after spirited driving. Ugh...always something.
 
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brodphish said:
I finally had some time to look into this further. My favorite local speed shop has an old-timer whose replaced a lot of Mopar big - block main seals, they said it would be 1 -2 days of labor. That seems expensive to fix what is just an irritation. I would likely do it but it seems the issue may arise again if not done exactly right with the right parts (ands that does not seem clear).

Maybe I'll go the baby diaper route. But it's starting to make me a little crazy.
Click to expand...
I was watching this thread in hopes of simpler solution. I get the crazy part. now I guess I'll get the diaper part... :-(
 
I would like to see what you guys used as a bracket for a diaper. Mine has a slow drip, and assuming I find it is actually the main seal, I might need a band-aid until fall.
The leak is so small it's mostly a nuisance, but leaves a nickle-sized spot that almost got me sidelined at the track last week.

Anybody got a good trick for tracing the source of a leak in that area? I have laid under the car waiting for it to drip and nada...then I give up, and there it is on ground, and one little droplet on the bottom edge of the inspection cover!
I never can tell where it starts!
 
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KnuckleDuster said:
I would like to see what you guys used as a bracket for a diaper. Mine has a slow drip, and assuming I find it is actually the main seal, I might need a band-aid until fall.
The leak is so small it's mostly a nuisance, but leaves a nickle-sized spot that almost got me sidelined at the track last week.

Anybody got a good trick for tracing the source of a leak in that area? I have laid under the car waiting for it to drip and nada...then I give up, and there it is on ground, and one little droplet on the bottom edge of the inspection cover!
I never can tell where it starts!
Click to expand...

A trick I use sometimes is to clean the area and spray it with a little fresh spray paint then drive it.
The oil will leave tracks in the new paint and you can most times find the source right away.
 
I seal the engine then pressurize with a source of regulated air;no more than 4 psi. Then with a spritze bottle with a good load of dish-soap, I start spritzing everything in sight. Course, the first time I do this,the engine is still on the stand,lol.
 
brodphish said:
I finally had some time to look into this further. My favorite local speed shop has an old-timer whose replaced a lot of Mopar big - block main seals, they said it would be 1 -2 days of labor. That seems expensive to fix what is just an irritation. I would likely do it but it seems the issue may arise again if not done exactly right with the right parts (ands that does not seem clear).

Maybe I'll go the baby diaper route. But it's starting to make me a little crazy.
Click to expand...
Find a different place to replace the rear seal cause if an experienced guy can't replace that seal in 4 hours he is having some very long naps. Kim
 
Any diaper bracket pics?
I'm sure I could come up with something, but yours might be cooler!
 
jimjimjimmy said:
it can be done in the car but first make sure your 100% sure its the seal . first check the valve covers oil sending unit and the back of the intake manifold for leaks .wipe everything down good first .
Click to expand...

I second this.... had the same issue, thought it was the rear main.... but closer inspection showed that the oil pressure sender was leaking.... installed a electric sender... don't have to worry about that crap hose anymore!
 
Internet hearsay... I've always heard foot-spray, like Desitin, was a great leak finder.
Sprays on white, dries quick. Leaks show up easily. Cleans up with water.

Steve
 
Valve cover gasket, hidden by the brake booster and headers.
Cleaned it off and got it installed correctly, no goo of any kind.
Let it run for 15 minutes and cool for 30 with cardboard under it. Not one drop!
VERY happy I'm not pulling my pan in the car!
 
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