Well It Leaks AGAIN!

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superchargeddrt

superchargeddrt

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Well,
The rear main seal leak on the Dart gas returned. I am beyond frustrated. I have had this engine out 3 times already. I put the Superformance seal in and it worked great for several months but now the leak has returned and I had to have the Dart flatbeded home. I am currently in Larry's truck heading to Carlisle, I'll have fun but it's just not the same without your car Larry's brother Bob thinks it could be the fact that the Dart runs at 70 PSI at highway speeds and the high pressure coupled with the temperature caused the main seal to fail. He thinks I should go with a stock pump, what do you guys think?
 
Wow that sucks! Sorry to read. In my opinion 70 psi ain't high. Not sure that helps you. Our 273 runs around 60 I believe.
 
superchargeddrt said:
Well,
The rear main seal leak on the Dart gas returned. I am beyond frustrated. I have had this engine out 3 times already. I put the Superformance seal in and it worked great for several months but now the leak has returned and I had to have the Dart flatbeded home. I am currently in Larry's truck heading to Carlisle, I'll have fun but it's just not the same without your car Larry's brother Bob thinks it could be the fact that the Dart runs at 70 PSI at highway speeds and the high pressure coupled with the temperature caused the main seal to fail. He thinks I should go with a stock pump, what do you guys think?
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Has NOTHING to do with high oil pressure. Why? Because there is a steel lip or "shield" that is part of the rear main journal that ensures a direct jet of oil does not hit the rear main seal directly.

I would be more worried about blowby or cylinder seal if it were mine. J.Rob
 
Try the rear main seal out of a Magnum engine.

The crank rear main seal journal is slightly smaller on the Magnum versus the LA making the seal slightly larger creating a tighter grip on the crank when used on the LA.

It is also made of a softer silicone rubber.

It worked on my '69 340.
 
how is the surfaces it is sealing against? Polished, smooth or a groove worn in from decades of use? was it turned at any time? what does the old seal look like when you take it out? PHOTOS when you get back?
 
The crankcase ventilation (pcv) is one place to look, need to have good crossflow and make sure you don’t have positive pressure internally.
 
If it worked for a few months, then failed to the point where it leaked so bad it needed to be flat bedded home.......my guess is you’re going to find an area of the lip thats worn away.
Look at it carefully with a magnifying glass.

My experience has been when it’s an installation issue, they start leaking pretty much right away.
 
RAMM said:
Has NOTHING to do with high oil pressure. Why? Because there is a steel lip or "shield" that is part of the rear main journal that ensures a direct jet of oil does not hit the rear main seal directly.

I would be more worried about blowby or cylinder seal if it were mine. J.Rob
Click to expand...

Yep. It's building crank case pressure and finding the least path of resistance to get out. If you do fix that leak for good, it will find another path.

I bought a used engine in 1981. That thing would leak oil from everywhere. Sitting at a stop light that thing would have 3 or 4 leaks at one time.

I pulled it out and every single top ring was broken. Some joker had used a ridge reamer on it and then ran a hone through it. Took a .040 over bore to get it back to straight.

Look for blow by issues.
 
yellow rose said:
Yep. It's building crank case pressure and finding the least path of resistance to get out. If you do fix that leak for good, it will find another path.

I bought a used engine in 1981. That thing would leak oil from everywhere. Sitting at a stop light that thing would have 3 or 4 leaks at one time.

I pulled it out and every single top ring was broken. Some joker had used a ridge reamer on it and then ran a hone through it. Took a .040 over bore to get it back to straight.

Look for blow by issues.
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The engine is my brand new 418 (340 Based) Stroker. The engine has 700 miles on it. The bottom end was built by a highly recommend builder near me. I am running a PCV on one valve cover and a breather on the other. I wasn't pushing on the car but I was going 65 - 70 MPH and revving at 3000 RPM for an extended period of time.I wasn't leaking for the past several months (after installing the Superformance seal) but I was only driving it to and from a car show near my house and usually not over 50 MPH. I will investigate further when I get back from Carlisle. Thanks for everyone's help.
 
Sometimes a leaky oil pressure sending unit can look like a rear seal problem. I'd double check that too.
 
My question is also what does the crank look like, was it polished, if not that is your problem. You have to get rid of the grooves for the lip seal to work.
 
Sure it’s not the rear cam bearing seal? I can tell you from experience that if it ain’t in there right you’ll be thinking it’s the rear main seal over and over again.

Jake
 
superchargeddrt said:
Well,
The rear main seal leak on the Dart gas returned. I am beyond frustrated. I have had this engine out 3 times already. I put the Superformance seal in and it worked great for several months but now the leak has returned and I had to have the Dart flatbeded home. I am currently in Larry's truck heading to Carlisle, I'll have fun but it's just not the same without your car Larry's brother Bob thinks it could be the fact that the Dart runs at 70 PSI at highway speeds and the high pressure coupled with the temperature caused the main seal to fail. He thinks I should go with a stock pump, what do you guys think?
Click to expand...
not------
 
The rear main seal is not an area that sees oil pressure, so I don't think that has anything to do with it. Has this particular engine/crankshaft ever been leak free at the rear seal? Could it be a marine crank?
 
I should stay out of this conversation but had a Carlisle trip issues as well. The roads around there suck! On arrival I found a body plug laying on the floor of the trailer. Looked and wondered put in my pocket. Thought a bit it and it was from the driver door front wing window adjustment access and Also had the left rear wheel cylinder blow for no good reason. The car was strapped down on tire bonnets.

For your issues I am not a SB guy but sounds like a assembly or crankcase pressure issue.
 
Dana67Dart said:
how is the surfaces it is sealing against? Polished, smooth or a groove worn in from decades of use? was it turned at any time? what does the old seal look like when you take it out? PHOTOS when you get back?
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So true. You can replace main seals until you turn blue in the face, but you are wasting your time if the sealing surface isn't right.
 
harrisonm said:
So true. You can replace main seals until you turn blue in the face, but you are wasting your time if the sealing surface isn't right.
Click to expand...

I will look at the surface when we have it apart but this is a fresh engine (700 miles) with a brand Molnar crank in it. I am betting that my PCV system (stock style with a breather) isn't up to the task of a 418 stroker. Anyway you look at it the main seal has to be replaced do the engine has got to come OUT AGAIN aaaaarrrrgh.
 
Before pulling motor out why don’t you try the 2 pcv system one on each bank but one with the inbuilt breather, just to rule out pressure build up.
 
67 gt said:
Before pulling motor out why don’t you try the 2 pcv system one on each bank but one with the inbuilt breather, just to rule out pressure build up.
Click to expand...

I`d like to see a pic of that valve -------------------never heard of one like that !
 
superchargeddrt said:
Well,
The rear main seal leak on the Dart gas returned. I am beyond frustrated. I have had this engine out 3 times already. I put the Superformance seal in and it worked great for several months but now the leak has returned and I had to have the Dart flatbeded home. I am currently in Larry's truck heading to Carlisle, I'll have fun but it's just not the same without your car Larry's brother Bob thinks it could be the fact that the Dart runs at 70 PSI at highway speeds and the high pressure coupled with the temperature caused the main seal to fail. He thinks I should go with a stock pump, what do you guys think?
Click to expand...

Definitly something wrong if it blew so bad u had to trailer it home , sounds like u messed it up, or a plug blew _???
 
What PCV do you have now, OP? BTW, new parts is not a 100% guarantee.

Was the oil blowing in large volume past the seal, i.e. blowing out a lot? Knowing that is part of the diagnosis. If so, then look carefully to see if the seal actually moved out of place. That would seem like a lot of crankcase pressure, or the seal moving in the groove for some reason.
 
If it was line honed and they removed more than .003 or .005 off the rear cap..the seal becomes too big, needs shaved on ends , then install it offset with black rtv on ends.
 
MOPAROFFICIAL said:
If it was line honed and they removed more than .003 or .005 off the rear cap..the seal becomes too big, needs shaved on ends , then install it offset with black rtv on ends.
Click to expand...


This is another thing often missed. You MUST fit the seal. You don't need much crush on the seal. Too much crush is bad.
 
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