Rear Main Seal Install

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Mike69cuda

Mike69cuda

Mopar Moron
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Guys,

I am struggling with rear main seal replacement on my 74 360 engine in my 69 cuda. I am doing it with engine in the car. I have the red viton one. The seal is about 0.050 inches proud or so when installed out of the box. It is way to big. My 68 FSM says to cut it off flush. I have read a lot of posts on this that say 0.010 in is max. It is very hard to trim that much off with the big steel retainer in the seal. I butchered the first one with a dremel.

How do I trim the seal?
 
Mike69cuda said:
Guys,

I am struggling with rear main seal replacement on my 74 360 engine in my 69 cuda. I am doing it with engine in the car. I have the red viton one. The seal is about 0.050 inches proud or so when installed out of the box. It is way to big. My 68 FSM says to cut it off flush. I have read a lot of posts on this that say 0.010 in is max. It is very hard to trim that much off with the big steel retainer in the seal. I butchered the first one with a dremel.

How do I trim the seal?
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The FSM is talking about trimming a "rope" type seal. You're using a Viton one. Just make sure the lip is facing the correct direction and you're good, if it's not it'll leak like a sieve.
 
With all main seals there a certain amount of "crush" when installing the cap. This keeps it tight.
 
That’s way too much crush and it will likely leak.
You need to CAREFULLY grind a little of each end of the seal until you get about .010 or so proud. Same for the cap.
 
I need to ask a question. Is there a bit of a groove and/or ring mark in the crankshaft where the journal spun against the seal? If there is, there is a chance that the new seal could leak too. After a hundred million revolutions, the seal will wear down, but it can wear a bit of a groove in the crank too. I once replaced one in a Jeep 4.0 straight 6, and there was a pretty good groove in the crank. After several hours of nasty, dirty work, the new seal leaked also.
 
harrisonm said:
I need to ask a question. Is there a bit of a groove and/or ring mark in the crankshaft where the journal spun against the seal? If there is, there is a chance that the new seal could leak too. After a hundred million revolutions, the seal will wear down, but it can wear a bit of a groove in the crank too. I once replaced one in a Jeep 4.0 straight 6, and there was a pretty good groove in the crank. After several hours of nasty, dirty work, the new seal leaked also.
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I will look. I have replaced it once and botched it. I am going to tear it down again and be more careful.
 
Mike69cuda said:
Do I need to cut both sides, or can I take it off one side? Any techniques suggestions?
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Yep...take a little off easy side very slowly. You don’t want to melt the rubber. You want to take as close to an equal amount off each side because the seal isn’t perfectly round out of the box. That’s so when it gets crushed when the cap is bolted on it will be round.

That’s why having too much crush is a bad thing...it forces the seal out of round when you put the cap on and it leaks.

If you get too little crush it will leak. So just sneak up on it. Make sure once you fit a half to the cap or block don’t switch the, as the cap may not be the same as the block.

I use a 1 inch belt sander to get my seals to size. Go slow, keep some water handy to cool it off and don’t melt the rubber or polymer or whatever they are made of.

Also take care to keep the ends square. This stuff doesn’t need to be perfect, but the more square you can keep it the better.

It’s actually easier than it sounds. So .010-.015 on each end proud and do the both halves and you’ll be golden.
 
Just got off the phone with Felpro tech support. They told me that the 360 rear main seal was designed to be used as supplied with no trimming. This is part# BS 40651.

I have been researching this a lot and have found no evidence of anyone trimming this particular seal. It is designed with the metal ring slightly below the surface of the seal half ends to allow for the Viton to compress slightly when put together. I could not figure out a way to duplicate this after trimming, so I kept searching for more info. According to felpro, the seal is designed to protrude .060 inches or more prior to assembly.
 
Mike69cuda said:
Just got off the phone with Felpro tech support. They told me that the 360 rear main seal was designed to be used as supplied with no trimming. This is part# BS 40651.

I have been researching this a lot and have found no evidence of anyone trimming this particular seal. It is designed with the metal ring slightly below the surface of the seal half ends to allow for the Viton to compress slightly when put together. I could not figure out a way to duplicate this after trimming, so I kept searching for more info. According to felpro, the seal is designed to protrude .060 inches or more prior to assembly.
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Call that moron back and ask him how you fit the seal when the block has been line honed. Then ask the moron how many engines he has personally assembled that has been lined honed and didn’t fit the gasket. See what he says.

I can tell you I’ve fixed so many of them it’s really insane that stooge doesn’t know better.

That’s why the one piece seal is a bit better. It’s not nearly as sensitive to line honing as the 2 piece seal is.

It doesn’t matter to me if you fit it or not. But this I’m sure of. If your seal is more than .010 proud of the block or cap, when you torque it down it will go out of round.

If you run into the issue of the seal being too proud, put it the cap and block and torque it on and look with your eyes and see if it’s round. The more crush the seal has the more out of round it will go.

If you do that and it’s not out of round, chances are it will seal.
 
yellow rose said:
Call that moron back and ask him how you fit the seal when the block has been line honed. Then ask the moron how many engines he has personally assembled that has been lined honed and didn’t fit the gasket. See what he says.

I can tell you I’ve fixed so many of them it’s really insane that stooge doesn’t know better.

That’s why the one piece seal is a bit better. It’s not nearly as sensitive to line honing as the 2 piece seal is.

It doesn’t matter to me if you fit it or not. But this I’m sure of. If your seal is more than .010 proud of the block or cap, when you torque it down it will go out of round.

If you run into the issue of the seal being too proud, put it the cap and block and torque it on and look with your eyes and see if it’s round. The more crush the seal has the more out of round it will go.

If you do that and it’s not out of round, chances are it will seal.
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I am not an engine builder, so I have little experience in this area. How much would be typically machined off the caps prior to a line bore?

Engine is in the car, so I can’t see anything with the cap on.
 
Mike69cuda said:
I am not an engine builder, so I have little experience in this area. How much would be typically machined off the caps prior to a line bore?

Engine is in the car, so I can’t see anything with the cap on.
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It depends. But cutting a couple off the cap will move the hole...damn I don’t remember. How far is the seal proud of the cap since you can see it?
 
Here is the 360 seal I have. Not sure why there is an extra 1/2. Maybe 1 is shorter or u get a second chance to get it right. Kim

2CC65D2A-8848-4994-B0CA-7CF97D78579F.jpeg


E7E8D4AD-737C-4CDC-83AE-FC109F0108AD.jpeg
 
Mike69cuda said:
Just got off the phone with Felpro tech support. They told me that the 360 rear main seal was designed to be used as supplied with no trimming. This is part# BS 40651.

I have been researching this a lot and have found no evidence of anyone trimming this particular seal. It is designed with the metal ring slightly below the surface of the seal half ends to allow for the Viton to compress slightly when put together. I could not figure out a way to duplicate this after trimming, so I kept searching for more info. According to felpro, the seal is designed to protrude .060 inches or more prior to assembly.
Click to expand...

They are correct. Also, the "correctest" to do this is with the engine out and upside down on a stand. Good grief man. You're talking about maybe 20 bolts here. With what you're trying to do, it's probably going to leak no matter what.
 
Just take the seal back out and try it in the cap if u havent already. How does it fit there? How does the other 1/2 fit in the cap? Shorten it if it needs it. In all my years I have never had to shorten a rear seal. I have never had a leak either. Even on a line bored block. Kim
 
I am going to put it in as is & see how it goes. As you can see in the picture it has a pretty large steel stiffener in the seal. It sets several thousands below the end of the seal on each end.

I tried to cut off the first one and it is really difficult. Messed it up. No way to recreate the rod Clearance below the seal end Surface doing that (assuming that is an intended feature of the part to help sealing).

No info anywhere on the internet about trimming it. All the feedback on the sales I found said it works great. My conclusion is that this particular seal is not designed to be trimmed.

I am a shade tree mechanic at best, so my opinion on this has very little merit at best. However even in in the case of align boring where they shave a few Thousandths max off the caps, I can’t see where the seal at 3 inches ID would be sensitive to that.

Going to assemble this week, so I will post results. Success for me will be a few drips rather than a puddle....

45F3A8B8-CDFB-413B-8C72-9317C571E319.jpeg
 
yellow rose said:
Are those 3 seals the same? Could just be the picture but that bottom seal looks bigger and it is a different diameter.
Damn glasses may be tricking me. That happens.
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YR, I haven’t used it yet and never paid very close attention to it. Just found it odd that there are 3 pieces. Kim
 
Mike69cuda said:
I am going to put it in as is & see how it goes. As you can see in the picture it has a pretty large steel stiffener in the seal. It sets several thousands below the end of the seal on each end.

I tried to cut off the first one and it is really difficult. Messed it up. No way to recreate the rod Clearance below the seal end Surface doing that (assuming that is an intended feature of the part to help sealing).

No info anywhere on the internet about trimming it. All the feedback on the sales I found said it works great. My conclusion is that this particular seal is not designed to be trimmed.

I am a shade tree mechanic at best, so my opinion on this has very little merit at best. However even in in the case of align boring where they shave a few Thousandths max off the caps, I can’t see where the seal at 3 inches ID would be sensitive to that.

Going to assemble this week, so I will post results. Success for me will be a few drips rather than a puddle....

View attachment 1715562427
Click to expand...

If you have a few hours I’ll go out to the shop and pull a cap off of a block and stick a seal in it and see what it looks like and take some pictures.
 
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