The Official Rear Main Seal replacement thread

[Rick69]

Hi! Hope everyone is healthy.
Doing my first rear main in a 440 on my back in the garage. The engine is stock.
The leak was not there at idle but started to drip when increasing the RPM.
All dry above from the valve covers and pressure switch.
I dropped the pan and windage tray. Removed the seal cap. Surprised at how easy the upper half came out!! It is a Fel Pro part #P-91020-1. Black.
Also, I noticed there were no side seals. The grooves were filled with black RTV. Anyone doing that?
I have a Mr. Gasket Seal Kit #1968. Is this a good option? Should I order a Fel Pro kit?
I am planning to install using the side seals. Should I be putting RTV on the side seals when I install?
I do have Locktite 518 for the seal ends when I reinstall.
Any comments and advice are welcome. All the posts are great.

 

[4406bbl]

For a while the rear main seals came without side seals. They gave you a tube of rtv, and some pipe cleaners to push the silicone in and had you fill the groove. I never tried that but that may be how yours was done.

 

[67MPRFAN]

I use a fel-pro two piece and I don't use the two side groove pieces they come with. Instead I just use a bunch of silicone on the sides. I don't offset the two half seals that ride on the crankshaft either I have heard some people suggest that but I don't

This is a text from the guy that built my last engine never had a leak in 4 years of owning the motor

 

[CompSyn]

So I've read through this tread. My question remains, is there any solid evidence to suggest one type a seal material is better or lasts longer than another? My time is now to decide on the right rear main seal combo for my build. I currently have the common black rubber seal with wax side sticks that comes in the Mopar engine tear-down gasket set. Is this completely inferior to other available options today?

Looking at Summit Racing, I see these other options...

Fel-Pro - Fluoroelastomer #2947
Fel-Pro - Rubber #BS40240
Fel-Pro - Rope #BS117480
Cometic - Viton #C5686
SCE - Silicone #16405
Mr. Gasket - Silicone #1968

Also, the side seals? Straight up silicone sealant, blue plastic strips or wax cardboard???

 

[khryslerkid]

I used the Viton seal kit from 440 Source. Following the directions to the letter and its been great with no leaks. The only thing that I found out after I installed it was to make sure you fill the seal retainer bolt holes with sealant. If not it will leave a void for oil to seep through under the gasket.

Mancini has the Viton seal kit also. Download the instructions from the first page in this thread.

 

[khryslerkid]

This pan gasket is really nice also. Mancini is the only place I could find it. I had to wait for awhile to receive it because of the Covid 19 shipping slowdown. I'm really pleased with it also.

 

[CompSyn]

Nick's Garage just did a great segment on fixing a big block rear main seal leak (start at 16:08):

Does anyone know the part number of the blue Fel-Pro side seals Nick used in the video? I’ve looked around but can’t seem to find them?

Also, has anyone made they’re own locator pins like Nick’s. What size bolt is that? I see that Indy offers the pins with their kit. Seems like a good way of lining up the seals...

 

[Stereolab42]

Interesting update to the Nick's Garage video above... in a subsequent video he had the engine on the dyno and admitted the rear main he thought he fixed started leaking again. Stated it wasn't a bad leak and that he had done his absolute best and some engines just can't be made leak-free. (I hope his customer was equally as understanding.) I was actually glad to see this since the very same thing happened to my engine... started leaking a small amount again after a few weeks. I "fixed" the issue by buying a Summit engine diaper and cutting it to fit around just the trans pan and bottom of the bell housing. Inconspicuous and with the leak being only a thimbleful or so every 100 miles it will take the diaper pad 100 years to need replacement. Oh well.

 

[Pistol Pete]

In my 383 I had:

one black seal (installed by a shop) and it leaked.
one Viton seal (installed by a shop) and it leaked.
one Viton seal (installed by me) and it leaked.

I finally gave up and installed a rope seal and viola, no leaks.

Sometimes you just gotta go old school.

 

[Challenger340]

So I've read through this tread. My question remains, is there any solid evidence to suggest one type a seal material is better or lasts longer than another? My time is now to decide on the right rear main seal combo for my build. I currently have the common black rubber seal with wax side sticks that comes in the Mopar engine tear-down gasket set. Is this completely inferior to other available options today?

Looking at Summit Racing, I see these other options...

Fel-Pro - Fluoroelastomer #2947
Fel-Pro - Rubber #BS40240
Fel-Pro - Rope #BS117480
Cometic - Viton #C5686
SCE - Silicone #16405
Mr. Gasket - Silicone #1968

Also, the side seals? Straight up silicone sealant, blue plastic strips or wax cardboard???

In my experience the Seal 'material' itself makes absolutely no difference whatsoever, because the 'Seal" itself is NOT the problem with Rear Main Seal 'leaks' in BB Mopars.
I've posted this many times here and over at DC.com.... 90% of the Rear Main Seal leaks in BB Mopars is NOT paying attention to the Seal Groove 'offset' presernt in ALL the Blocks, which if you just slap it together without paying attention to it will leak to some extent about 40% of the time..... Seal 'material' don't matter a hill 'O beans and if you believe it does because some 'expert' told ya so..... that guy is a moron !
You Can believe whatever you want ?
All I'm saying is all I've ever used is the cjheapest std Seal... and the stock Seal Retainers.... heading North of 300 BB Mopars and the lasty 250 or so didn't leak after I figured it out....
But again, you can believe whatever or whomever you wish.

Go LOOK for yourself....
* Put a Seal half(any seal) in the block flush with the part lines
* Put the Crank in the Block with a couple of main brgs.... just sit it in there with no caps
* LOOK at how compressed the Lip on the Seal is on the Crank on Both sides and compare
* SEE how one side is sealing up against the Crank.... and the other side of the Lip Seal is barely touching/sealing against the Crank ?
How the F**k is the Seal 'material' used going to change THAT ????????

 

[luvthyapril]

Well I read this thread with great interest as I will be building my first mopar big block but not sure which way to go yet other then using what was originally used for the rear main seal but I do know I don't want a leaker.

 

[CompSyn]

In my experience the Seal 'material' itself makes absolutely no difference whatsoever, because the 'Seal" itself is NOT the problem with Rear Main Seal 'leaks' in BB Mopars.
I've posted this many times here and over at DC.com.... 90% of the Rear Main Seal leaks in BB Mopars is NOT paying attention to the Seal Groove 'offset' presernt in ALL the Blocks, which if you just slap it together without paying attention to it will leak to some extent about 40% of the time..... Seal 'material' don't matter a hill 'O beans and if you believe it does because some 'expert' told ya so..... that guy is a moron !
You Can believe whatever you want ?
All I'm saying is all I've ever used is the cjheapest std Seal... and the stock Seal Retainers.... heading North of 300 BB Mopars and the lasty 250 or so didn't leak after I figured it out....
But again, you can believe whatever or whomever you wish.

Go LOOK for yourself....
* Put a Seal half(any seal) in the block flush with the part lines
* Put the Crank in the Block with a couple of main brgs.... just sit it in there with no caps
* LOOK at how compressed the Lip on the Seal is on the Crank on Both sides and compare
* SEE how one side is sealing up against the Crank.... and the other side of the Lip Seal is barely touching/sealing against the Crank ?
How the F**k is the Seal 'material' used going to change THAT ????????

Bob, previously, I have read your posts here and at dodgecharger.com about the rear main seal channel being improperly offset in the the block to the the determent of the sealing capability of the rear main seal. I appreciate you sharing your experience with this. Thank you. It's something I don't know that I would have looked for under my own volition. So I will be looking at that for sure with my block. To clarify, are you saying that once one addresses this issue with this offset, that the common (1) black rubber seal, (2) factory retainer, and (3) wax-cardboard side seals makes for many years of leak-free happy motoring? No need to overthink it beyond that?

Also, since this tread specifically relates to rear main seal leaks, so I don't hijack it, I'd like to start another thread on trips and tricks for sealing up the rest of the short block assembly as it relates to the oil pan gasket and with windage tray, timing chain cover, fuel pump, distributor, other?, etc...

The Official B/RB Short-Block Leak Free Thread - LINK

 

[khryslerkid]

In my experience the Seal 'material' itself makes absolutely no difference whatsoever, because the 'Seal" itself is NOT the problem with Rear Main Seal 'leaks' in BB Mopars.
I've posted this many times here and over at DC.com.... 90% of the Rear Main Seal leaks in BB Mopars is NOT paying attention to the Seal Groove 'offset' presernt in ALL the Blocks, which if you just slap it together without paying attention to it will leak to some extent about 40% of the time..... Seal 'material' don't matter a hill 'O beans and if you believe it does because some 'expert' told ya so..... that guy is a moron !
You Can believe whatever you want ?
All I'm saying is all I've ever used is the cjheapest std Seal... and the stock Seal Retainers.... heading North of 300 BB Mopars and the lasty 250 or so didn't leak after I figured it out....
But again, you can believe whatever or whomever you wish.

Go LOOK for yourself....
* Put a Seal half(any seal) in the block flush with the part lines
* Put the Crank in the Block with a couple of main brgs.... just sit it in there with no caps
* LOOK at how compressed the Lip on the Seal is on the Crank on Both sides and compare
* SEE how one side is sealing up against the Crank.... and the other side of the Lip Seal is barely touching/sealing against the Crank ?
How the F**k is the Seal 'material' used going to change THAT ????????

Bob, previously, I have read your posts here and at dodgecharger.com about the rear main seal channel being improperly offset in the the block to the the determent of the sealing capability of the rear main seal. I appreciate you sharing your experience with this. Thank you. It's something I don't know that I would have looked for under my own volition. So I will be looking at that for sure with my block. To clarify, are you saying that once one addresses this issue with this offset, that the common (1) black rubber seal, (2) factory retainer, and (3) wax-cardboard side seals makes for many years of leak-free happy motoring? No need to overthink it beyond that?

Also, since this tread specifically relates to rear main seal leaks, so I don't hijack it, I'd like to start another thread on trips and tricks for sealing up the rest of the short block assembly as it relates to the oil pan gasket and with windage tray, timing chain cover, fuel pump, distributor, other?, etc.

The offset is covered in the instructions in post #13. You can download the instructions from post #9 in this thread.

 

[demonram]

I’ve got a leaker. The engine was put together 9 years ago. It’s a stroked 400 to 451. It is a Viton seal installed by the shop. It started about two years ago, very small, now it’s bad. Of course it’s got to be change. What are my options while it’s in the car. I did do a factory rope seal on big block many years ago, no problems. This scares the crap out of me. Thanks in advance!

 

[hotroddinwillie]

Hi Guys,
I have experienced many of the trials and tribulations all of you have experienced with our beloved b/rb engines. I've had a few leakers for sure. I forget which issue of Mopar Action I read that offered a suggestion I have used two times with success. Chuck Senatore from Muscle Motors wrote the column and he stated to simply grind .010 off the parting line of the aluminum seal holder in a cap grinder. I used a file in a bench vise in my garage. I installed the black rubber standard fel pro seal. I did this on two engines that had no rear main seal leak.

 

[MarPar]

Hi Guys,
I have experienced many of the trials and tribulations all of you have experienced with our beloved b/rb engines. I've had a few leakers for sure. I forget which issue of Mopar Action I read that offered a suggestion I have used two times with success. Chuck Senatore from Muscle Motors wrote the column and he stated to simply grind .010 off the parting line of the aluminum seal holder in a cap grinder. I used a file in a bench vise in my garage. I installed the black rubber standard fel pro seal. I did this on two engines that had no rear main seal leak.

Willie, would you have an illustration or pic with arrows for us simpletons to visualize the area you speak of?

 

[themechanic]

I believe that technique was mentioned earlier in the thread.

 

[RAMM]

Interesting update to the Nick's Garage video above... in a subsequent video he had the engine on the dyno and admitted the rear main he thought he fixed started leaking again. Stated it wasn't a bad leak and that he had done his absolute best and some engines just can't be made leak-free. (I hope his customer was equally as understanding.) I was actually glad to see this since the very same thing happened to my engine... started leaking a small amount again after a few weeks. I "fixed" the issue by buying a Summit engine diaper and cutting it to fit around just the trans pan and bottom of the bell housing. Inconspicuous and with the leak being only a thimbleful or so every 100 miles it will take the diaper pad 100 years to need replacement. Oh well.

View attachment 964617

Well I have built many many big blocks over the last 20+ years and I ran into one that was a leaker. There is a thread on Moparts, this was back in 2015. I was blessed with a dyno and a VERY understanding customer. If this customer wasn't the original owner of a 4speed Roadrunner--I may have given up. I singlehandedly depleted all of the Mopar Bigblock oil pan gaskets in the warehouses Ont/Alberta that I have access to. I dyno'd and replaced the rear main seal 7 times. I went to a rope seal I think on attempt 3 or 4 and even it didn't work. I even sent the crank out for chrome build up on the seal surface $$$$. I watched the above video on Nick's Garage and he is grasping at straws and doesn't really understand the root problem--his guide pins aren't a bad idea but if you use the method that the late Monte Smith (RIP) shared with me you will have 100% success.


I could not stop the leak until I took the following measures: Use the stock retainer--The billet pieces are no better and actually may cause misalignment because they provide no "wiggle room". In order to line up the seal halves you need "wiggle room". First step I take is to glass bead rear main seal retainer to ensure 100% cleanliness. I mount the retainer in my Sunnen cap grinder and remove .004-.005" just to provide a perpendicular and fresh surface and maybe to add a little "crush" to the seal. Then I drill the retainer bolt holes oversize to provide aforementioned wiggle room. I use two chemical sealers in this process. With the crank in the block apply plenty of oil or assembly lube to the seal surface << very important. I use a clingy lube by Lucas so it doesn't drip into the seal receiver channel/groove in the block. Take one seal half (Doesn't matter the brand or part #) and apply Permatex Red anaerobic "jelly" to the back side of the seal and with the lip facing towards the front of the engine slide the seal around the crank and into the block groove. Align the seal parting line so the seal half is in the 6 o'clock and 12 o'clock position. Yes you read that right , where the seal halves meet will be "up and down" I know I was skeptical too until I realized what happens next. Take the other half of the seal, apply the same Red jelly to the back side AND the parting line faces (just a little blob) and slide it around the crank until it butts up against the seal you already have installed. You will now see the entire seal staring at you wrapped around the crank. Adjust the seals so the faces are aligned perfectly and you should even see a little jelly squeezed out. Now I take the seal retainer which is empty and clean and apply a little Permatex Right stuff black to the retainer 2 block face and I will even apply it to the sides of the retainer where the cardboard thingys used to go. Don't worry about sealing the sides yet-that comes later. Now when you go to install the seal the "wiggle room" I keep talking about comes into play. When you install the retainer use a light touch and as you slide it down onto the seal you will "feel" the seal pull and position the retainer into its natural position whether its right left for or aft. Now when you drop the bolts down the oversized holes will allow the retainer to stay in the position the seal halves "want" it to. Torque the bolts down to 10-15-20 lbs whatever snug and we're almost done with this process. Now I install a new tip on my tube of Right Stuff so I can "inject" sealant down into the side channels of the retainer. I pump it into the channel until I see it meet the block face and start to come out at the back of the block a little. I then take my finger and smear it downwards on each side of the crank flange and you're done. Let it set up for a couple days if you can and you shouldn't have a rear main leak as long as you don't have something else going on like too much crankcase pressure from poor cylinder seal. Oh and before you do this please make sure the #5 main is installed. J.Rob

 

[ChargerBob]

In my experience the Seal 'material' itself makes absolutely no difference whatsoever, because the 'Seal" itself is NOT the problem with Rear Main Seal 'leaks' in BB Mopars.
I've posted this many times here and over at DC.com.... 90% of the Rear Main Seal leaks in BB Mopars is NOT paying attention to the Seal Groove 'offset' presernt in ALL the Blocks, which if you just slap it together without paying attention to it will leak to some extent about 40% of the time..... Seal 'material' don't matter a hill 'O beans and if you believe it does because some 'expert' told ya so..... that guy is a moron !
You Can believe whatever you want ?
All I'm saying is all I've ever used is the cjheapest std Seal... and the stock Seal Retainers.... heading North of 300 BB Mopars and the lasty 250 or so didn't leak after I figured it out....
But again, you can believe whatever or whomever you wish.

Go LOOK for yourself....
* Put a Seal half(any seal) in the block flush with the part lines
* Put the Crank in the Block with a couple of main brgs.... just sit it in there with no caps
* LOOK at how compressed the Lip on the Seal is on the Crank on Both sides and compare
* SEE how one side is sealing up against the Crank.... and the other side of the Lip Seal is barely touching/sealing against the Crank ?
How the F**k is the Seal 'material' used going to change THAT ????????

That makes sense to me, do you recall what side of the block the retainer needs to be tweaked over to, (ie like tweaked over to the starter side) Thanks

 

[khryslerkid]

That makes sense to me, do you recall what side of the block the retainer needs to be tweaked over to, (ie like tweaked over to the starter side) Thanks

Hey Bob. It has to be measured. Post #13 explains how.