Author Topic: *THE* definitive guide to FE rear main seal installation  (Read 21200 times)

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*THE* definitive guide to FE rear main seal installation
« on: November 29, 2012, 10:26:38 AM »
Folks, I'd like to start a thread topic here on how you personally install your FE rear main seals to insure there is absolutely positively no leak.  I've done my rear main on my new 428 three times now and I'm still getting a 3" puddle under the car after a few days of sitting, so obviously I'm not doing something right.

On my last attempt I used the following process with no better results than my prior attempts:

1.  Clean the rear main cap spotlessly. 
2.  Install the upper seal in the cap, dab a small bit of Right Stuff on the upper seal surface that will contact the seal on the bottom (actually the top) seal already in the block.
3.  Use a super, super thin coat of copper coat sealant on the cap mating surface that will contact the block horizontally.  Never did this before, but figured with two failed attempts prior it was worth a try but obviously didn't help this time.
3.  Install cap into the block and torque to spec.
4.  Sand the side seals down until they will slide with a little effort all the way into the side seal bores.
5.  Lube up the side seals with Right-Stuff sealant and install them all the way in, minus 1/2" exposed above the cap surface.
6.  Drive the pins in and thus drive the side seals the rest of the way, use a small pin punch to make sure the pins are below the pan rail surface.
7.  When installing the windage tray and oil pan use a small smear of Right Stuff over the main cap edges and side seal holes.

There is this topc on the rear main crush, which I've never really paid attention to before, but maybe it's time to look into?

What are everyones thoughts on offsetting the upper and lower seals so they are not in line with the block and main cap mating surfaces?  Is this the secret trick?

I think this thread would be very beneficial to those searching out there for how to do this right.  There is a correct proceedure, step by step that we should be following to do this correctly and I know I would personally love to know what it is to make sure the rear main install goes smoothly the first time.  Thanks all!


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Re: *THE* definitive guide to FE rear main seal installation
« Reply #1 on: November 29, 2012, 12:41:09 PM »
I guess I have several random comments on this topic that weren't mentioned above:

- If you are using an aftermarket crank, they are not usually cut with the angled grooves in the crank where the seal rides.  Those grooves really help in pumping the oil away from the seal and preventing leaks. 

- With our engines, where they may be "exercised" more frequently at higher engine speeds, crankcase pressure can build to fairly high levels, and one place the oil will come out is through the rear main seal.  You need to look carefully at the amount of ventilation area you have for the crankcase; a lot of the breathers out there have two tiny little holes for air to escape the crankcase, and they are probably not big enough to prevent large pressure spikes in the crankcase.  I will see this a lot on the dyno, especially with large cubic inch, high horsepower engines, where the rear main will start showing some leaks after a few dyno pulls.  Also, on engines like this where a vacuum pump is used, you will rarely see the problem because the vacuum pump keeps a vacuum in the crankcase.

- Some stock blocks have a pin in the bottom of the seal bore to hold the original rope seal.  Engine builders will remove this pin to install a neoprene seal, but often not do a good job, and leave a nub at the bottom of the seal bore.  This pushes the seal out of shape, and can cause leaks.

- The seal vent in the rear main cap must be clear, or you will have leaks.  This often requires trimming the oil pan gasket and/or the windage tray to make sure the opening in the cap is clear.  On some Shelby blocks I have machined the rear main cap to enlarge this passage.

I always offset the rear main seal from the cap parting line, because that is what the instructions that come with Fel-Pro seals say you should do.  However, I have quit using the side seals, and have opted instead for sealer in these grooves.  I use Ford TA-31 sealer nowadays, although the Right Stuff is probably just as good.  After the cap is installed and torqued (and I make sure I put some sealer on the block between the seal groove and the corner of the cap), I just squirt some of that TA-31 into the side seal holes, and then use the side seals themselves to push it down into the bottom of the hole,  You will apply pressure to the side seals and can see the sealer coming out between the block and the cap as you go.  Squirt in more sealer and repeat until the hole if filled.  Then I will usually smear the sealer that has come out between the block and the cap over the joint, just for a little extra insurance.

Having said and done all this, I hate to say it but I still get minor rear seal leaks on some engines; I suspect its the aftermarket cranks without those grooves machined in, but it could be my technique too.  I'm also interested in comments from others on this topic.

Jay Brown
- 1969 Mach 1, Drag Week 2005 Winner NA/BB, 511" FE (10.60s @ 129); Drag Week 2007 Runner-Up PA/BB, 490" Supercharged FE (9.35 @ 151)
- 1964 Ford Galaxie, Drag Week 2009 Winner Modified NA (9.50s @ 143), 585" SOHC
- 1969 Shelby Clone, Drag Week 2015 Winner Modified NA (Average 8.98 @ 149), 585" SOHC



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Re: *THE* definitive guide to FE rear main seal installation
« Reply #2 on: November 29, 2012, 12:53:28 PM »
I used a thin coat of right stuff on the sides, bottom and especially the corner of the cap as well as the side seal seat. I ended up doing my rear main twice as I could not ensure the side seals were fully bottomed out after the pins were driven home. Turns out they were.. but I wanted to be sure and the few $$ for another seal were worth my piece of mind. To get the side seals in I installed the cap with the side seals almost fully seated on the cap(just 1/4 inch protruding) and made sure they stayed there as I installed the cap. Gotta go slow but it can be done. After that when I drove the pins home and saw the side seals get pulled in the remaining 1/4 inch by the pins, I knew they were all the way at the bottom.

I offset the upper and lower as well as putting a small dab of right stuff on each end. It does not need to be offset much.. just enough so the seal is not perfectly in line with the main cap. I'd also recommend using a small amount of engine or assembly oil when installing the upper half of the seal if doing so while the crank is installed. It's a tight fit and you don't want to damage any of the seal seating surfaces as it's being installed. I would not recommend using right stuff on the outer sealing surface as it might actually interfere with the seals functionality.  I also put a thin coat of right stuff at the front of the cap with my finger along the cap/block interface at the sides and bottom. Did not take many pics of the rear cap.. but you can barely make out the right stuff smeared at the seam in this pic.

Overkill perhaps.. but I'll take the cheap additional insurance as opposed to trying to do that seal on the car.


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Re: *THE* definitive guide to FE rear main seal installation
« Reply #3 on: November 29, 2012, 06:55:44 PM »
I too have fought and lost this battle more than once.

The technique I have developed which works well for me is pretty much a combination of several of the previously detailed techniques.

First, I clean everything to the point where I wouldn't feel bad about putting the stuff in my mouth.

Then I'll install the seal halves cocked at about 2 o'clock/8 o'clock. I'll put a small dab of silicone on the end of the mating points of the two seals.

Then I'll drop the cap in, putting a small smear of silicone on the mating faces first.

Once the cap is in place and torqued in sequence with the other caps, I'll inject some silicone into the end seal slots, using the pencil tip extension that comes with the tube to get down as deep as I can.

After that, I'll push the rubber end seals in as deep as I can, which usually forces some silicone out through the mating surfaces of the cap and block. Once the rubber seals quit progressing, I'll use the little metal nails and a small hammer to drive the seal the rest of the way in. This will typically force more silicone out, which I'll then wipe off. If the seals and nails don't go all the way in, I'll cut off the excess.

Then, before I drop the gasket on, I'll put a little extra dab of silicone on the main cap parting line.

Works for me so far.

Interesting to read the thoughts on breather cap efficiency and the lack of cross-hatching on aftermarket cranks. These both make a lot of sense.


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Re: *THE* definitive guide to FE rear main seal installation
« Reply #4 on: November 29, 2012, 08:37:13 PM »
I had my aftermarket FE crank prepped by Gessford machine, one of the procedures they did was to machine the diagonal sipe groves on the rear main seal surface.
as for crankcase venting on hi compression FEs, I install a hose nipple in the mechanical fuel pump block off and tee it into my evac tube to the header collector.
1956 Ford Gasser 427FE
1966 Fairlane
1966 Bronco supercharged