Two-piece rear main seals

[D60]

This is a Dodge 318 but obviously applicable to the 350, Jeep 4.0 etc

Do you recommend "offsetting" the seal so the split is not at the seam of the bearing cap?

I was always told to do this, but then do you worry about nicking it as one side of the seal must travel into the upper half without the benefit of the "Sneaky Pete" tool?

I'm wondering if it's safer to install it dead even with the cap halves and just rely on a couple dabs of silicone?

 

[PontiacHO]

No. It does nothing. Install the seal in the factory method. (Both halves seated in the block and main cap). Apply a very slight glaze of RTV on the seal ends where they meet as well as the rear main bearing cap and block. Cocking the seal opens the door to assembly issues and a really bad oil leak.

 

[Trav]

You may find this helpful. the only ones I ever trimmed to the joint were old rope seals, on front rope seals in the cover they were trimmed on a slant and pieced together so there was no split.

https://www.felpro.com/technical/tecblogs/how-to-install-rear-main-seal.html

 

[SwampSurvivor]

I'm just happy to get the top half in without tearing or ripping it.

My jeep 4.0 had the winged seal on it so I didn't have an option to offset.

 

[NYEngineer]

When I was young I worked in a marine engine machine shop. During the winter we built countless small block chevys for the Mercruiser warranty program. I was shown to offset the rear main seal slightly, like 5/16 of an inch. Add a slight dab of RTV to the ends and carefully assemble the main cap. Never had an issue. No leaks, no comebacks. That being said, I'm sure Pontiac HO is also correct in saying just do it as the factory does.

 

[emmett442]

Doesn't make a difference either way, in my opinion. Done right, the traditional method of installing flush doesn't leak, so I don't try to reinvent the wheel by offsetting.

 

[D60]

You may find this helpful. the only ones I ever trimmed to the joint were old rope seals, on front rope seals in the cover they were trimmed on a slant and pieced together so there was no split.

https://www.felpro.com/technical/tecblogs/how-to-install-rear-main-seal.html

It's interesting because Fel-Pro specifically says 3/8" offset.

They also say to use the tool to install the top half, so it still begs the question of why the tool is necessary for the top half but never mind when starting the bottom half

 

[Trav]

It's interesting because Fel-Pro specifically says 3/8" offset.

They also say to use the tool to install the top half, so it still begs the question of why the tool is necessary for the top half but never mind when starting the bottom half

Some sort of Chinese finger tool? No needed for the lower half.

 

[t1snwrbrdr12]

I’ve done a lot of jeep 4.0s and never installed them any way but flush / even. Never had a comeback in the 11 years I worked at the Jeep dealer.

 

[Dinoburner]

The concern here is that offsetting the seals could end up with a gap then leak however no one here so far has had a problem. If I ever do another rebuild I`ll flush mount the seals.

 

[D60]

Some sort of Chinese finger tool? No needed for the lower half.

Just saying it's gotta go in 3/8" on one side if you clock it 3/8" lopsided.

No matter, I'll play it by ear and see what I think

 

[Trav]

I cant see any problem doing that with rubber seals, it isn't happening with rope seals though.

 

[Exhaustgases]

When I was young I worked in a marine engine machine shop. During the winter we built countless small block chevys for the Mercruiser warranty program. I was shown to offset the rear main seal slightly, like 5/16 of an inch. Add a slight dab of RTV to the ends and carefully assemble the main cap. Never had an issue. No leaks, no comebacks. That being said, I'm sure Pontiac HO is also correct in saying just do it as the factory does.

RTV ? So then zero oil was present when doing this?

 

[clinebarger]

It's interesting because Fel-Pro specifically says 3/8" offset.

They also say to use the tool to install the top half, so it still begs the question of why the tool is necessary for the top half but never mind when starting the bottom half

I install them straight up & use a little Hylomar M on the seal & main cap.....You can get weeping through the main cap to block interface.

The blue Fel-Pro material swells in service/contact with oil, I pretty much stopped using Fel-Pro if I can help it.

All 2 piece seals will weep oil, It's the nature of the design.

 

[D60]

I install them straight up & use a little Hylomar M on the seal & main cap.....You can get weeping through the main cap to block interface.

The blue Fel-Pro material swells in service/contact with oil, I pretty much stopped using Fel-Pro if I can help it.

All 2 piece seals will weep oil, It's the nature of the design.

I have a Mahle set but it didn't come with the little shoehorn. I believe FailPro does so I may order one just to get the plastic shoehorn.

I could probably fashion one if I felt like messing with it. I guess some guys use a plastic straw.

The instructions included with the Mahle say nothing about offsetting, but does say to leave the ends of the seal halves dry. I may use a little anaerobic on the seal joint anyway as I doubt matters. I'll probably use anaerobic on the bearing cap, too (vs RTV). I don't have any Hylomar and keep meaning to order some.

 

[D60]

Also, appreciate all the perspectives here. I think it's cool to hear people's various approaches. In time we develop our own methods, usually based mostly on experience and maybe a touch of superstition along the way, at least for me.

I've helped friends replace 2-piece rear mains before but let them make their own calls on things like this because I don't want to "own it" if it leaks. Yet somehow this is the first one I've done myself.

 

[Olds394]

Best Gaskets Co. has saved me numerous times.

 

[t1snwrbrdr12]

I’ve always installed with sil-glyed or assembly lube to aid and reduce chance of damage. Also used the tip of a zip tie where the upper seal is initially going in to shield the new seal from the sharp edge of the block.

 

[NYEngineer]

RTV ? So then zero oil was present when doing this?

These were always on new engine assemblies on an engine stand in the shop. I don't ever remember replacing a rear seal in a boat. (I'm sure it can't really even be done. The engine would be pulled but we never replaced rear seals.)
We added a slight film of grease to the surface that touches the crankshaft. The back of the seal got the lightest application of blue RTV as did the ends. I mean LIGHT. None of these ever leaked.
The very few rear seals I have done with an engine in place ( in a vehicle) were done the same way. I would spray starting fluid around the top of the crank so it was clean when the new seal was rolled in. Grease on the sealing surface, light RTV on the back, cap goes on with the other half.

 

[D60]

Ok well I wound up installing it flush with the bearing cap seam.

My belief/theory after this research is that it doesn't really matter, and the old one came out flush.

After a brief test drive to get it up to temp I shut it down on my concrete floor and haven't observed any leaking yet. One vid I watched noted you may see "residual leaks" for up to a week due to oil in the bellhousing, etc. I thought that was actually a good reminder to not panic immediately if some leaking occurs shortly after the repair.