1950s New rear main seals not sealing?

[Caddy Wizard]

There have been posts on the Forum about new rubber rear main seals not sealing (failing) on 40s and 50s Cadillac engines.  I have personally experienced this recently, as have others.

It has been speculated that the reason for the seals not sealing correctly is that the trough or recess into which the seal fits is not precision made (not held to tight tolerances when the engine was manufactured), while the new rubber seals are held to tight tolerances.  I believe this is the cause.  When the engine blocks were cast, the seal that was going in there was a rope seal that would be pounded/pressed into the trough, filling the trough very completely.  In short, it was jammed in there tightly.  So no oil could flow around the seal. It might flow past the face of the seal (between the seal and the crankshaft journal), but it was virtually impossible to flow around the seal.

Fast forward to today and the seals we are using (well, lots of us anyway) are dynamic lip rubber seals (with a steel wire core to hold shape).  These seals are made to precise dimensions and are not able to conform to the exact shape and size of the trough the way that the rope seals did and do.  If the seal doesn't fill the whole profile of the trough, pressurized oil can flow AROUND the seal and bypass the dynamic lip.  This is what I believe we have been experiencing when the dynamic lip rubber seals fail to seal completely.  Recently, I have even seen a new rubber seal fit so loosely in the trough that it can slide side to side a noticeable amount (this was on Bob Kielar's 55 FW).

To help the dynamic lip rubber seal fit tightly in the trough, we can use thin gasket paper (1/64" or 1/32") between the bottom of the seal and the trough and/or between the back of the seal and the trough.  We want to seal the 3 points of contact between the rubber seal and the 3 surfaces of the trough.  A key point to understand is that we want the forward point of contact (the one closest to the lip of the seal) to seal tightly against the side surface of the trough.  The attached drawings illustrate this point.

I believe that careful attention to this perhaps will prevent a new seal from leaking (but we are still having trouble with Bob Kielar's car). Maybe...

[The Tassie Devil(le)]

Not sure if this is the case with Cadillac or LaSalle, but I have found on many crankshafts that use the rope seal, there are small angled grooves machined into the crankshaft sealing surface, to promote the spinning crankshaft to keep the oil moving back into the engine.

These are not required with the new formed seals, and therefore there is always the possibility that oil could seep out, as the rubber does not go into these grooves.

Bruce.  

[Dave Shepherd]

Not sure if this is the case with Cadillac or LaSalle, but I have found on many crankshafts that use the rope seal, there are small angled grooves machined into the crankshaft sealing surface, to promote the spinning crankshaft to keep the oil moving back into the engine.

These are not required with the new formed seals, and therefore there is always the possibility that oil could seep out, as the rubber does not go into these grooves.

Bruce.  

Bruce,I have been dealing with that crank issue on cars in the shop over the years, best to stay with the rope type. Find a way, engine apart, to cutdown the grooves best possible. Will help the neoprene type seal work better, but not perfect.

[Chopper1942]

As I stated in an earlier post, there is nothing wrong with a rope seal. Of course they are easier to install when the crank is out, but I have replace many without removing the crank.

You need to soak the rope seal for a couple of weeks in oil. Use a small brass punch to start the upper seal out of the groove and then pull it out with pliers. Attach Chinese fingers to the seal and pull it into the upper groove. Cut seal off flush with the block surface. Use a wooden hammer handle, with a lot of pressure on the hadnle, to roll the seal into the main cap. Cut it off flush with the cap. Use some brake cleaner and clean the cap and block mating surfaces of all oil. Get some GMS sealer and put a very thin coat on the main cap and a small amount on each seal end. Install the cap and torque to specs.

Straighten any raised areas around the pan bolt holes. Clean all the oil off the block and pan. Put a thin coat of GMS on both sides of the pan gasket. Install the pan and gasket and TORQUE to specs. Let is set for 24 hours, so the GMS can fully cure, before adding oil and starting the engine.

[Caddy Wizard]

Not sure if this is the case with Cadillac or LaSalle, but I have found on many crankshafts that use the rope seal, there are small angled grooves machined into the crankshaft sealing surface, to promote the spinning crankshaft to keep the oil moving back into the engine.

These are not required with the new formed seals, and therefore there is always the possibility that oil could seep out, as the rubber does not go into these grooves.

Bruce.  

Cadillac OHV engines (1949 and up) don't have the "oil slinger" grooves machined into the rear of the crankshaft.

[Jay Friedman]

Cadillac OHV engines (1949 and up) don't have the "oil slinger" grooves machined into the crankshaft.

I don't think that is entirely correct.  I haven't looked at the crankshaft of a 1949 and up Cadillac OHV engine for some years, but if I remember there are oil slinger grooves machined into the FRONT of those crankshafts to keep oil away from the seal in the timing chain cover. 

[David King (kz78hy)]

Pictures stopped loading after 8.  I will add a few more once the site is fixed.

Yesterday my friend and I replaced the pan and rear main seals in the 55 I'm restoring.  I will post more photos on the restoration thread (if the photos will load).  The seals in place did not present with an obvious issue.  The seal to grooves in the block and cap were tight, no room for shim/gasket material.  I bought both of the seals discussed here to pick the one we thought would work best.  The seal removed looked to be the Best brand version.

We inspected the seals and we noticed the Best version did not match up well to itself where it meets.  There was an out of round condition and joint between the them was not molded with a perfect fit or matching surface, these had void in it.

The Felpro one was round and both halves matched together much better, so it was decided to use it.

The seal was slightly clocked in the groove to have one end extend ~3/16" to mate up the cap halve.

Once it was back together and tested, it was dry for the warmup run.  Fingers crossed this finally killed my oil leaking issue.

[Roger Zimmermann]

It seems that this is every body's problem, me included!

[Bob Kielar]

Pictures stopped loading after 8.  I will add a few more once the site is fixed.

Yesterday my friend and I replaced the pan and rear main seals in the 55 I'm restoring.  I will post more photos on the restoration thread (if the photos will load).  The seals in place did not present with an obvious issue.  The seal to grooves in the block and cap were tight, no room for shim/gasket material.  I bought both of the seals discussed here to pick the one we thought would work best.  The seal removed looked to be the Best brand version.

We inspecting the seals we noticed the Best version did not match up well to itself where it meets.  There was an out of round condition and joint between the them was not molded with a perfect fit or matching surface, these had void in it.

The Felpro one was round and both halves matched together much better, so it was decided to use it.

The seal was slightly clocked in the groove to have one end extend ~3/16" to mate up the cap halve.

Once it was back together and tested, it was dry for the warmup run.  Fingers crossed this finally killed my oil leaking

Hello David,
How did you trim the tabs off of the fel pro seal? Also did you use any sealant on the rear main seal?
Thanks,
Bob

[Cadillac Jack 82]

While I can agree to a certain extent that its due to the differences between then and now...I believe its because quite a few parts are manufactured by companies overseas who literally will take a photo and rough specs of a part and make a reproduction.  While this isn't always the case its the case with most parts I've sourced.  Too many manufacturers cut corners in order to squeeze out an extra bit of profit.

[David King (kz78hy)]

Hello David,
How did you trim the tabs off of the fel pro seal? Also did you use any sealant on the rear main seal?
Thanks,
Bob

Bob, the "wings" on the seal were trimmed off w/a razor blade.  A tiny bit of Loctite 518 flange sealant was used in the corners of the main bearing cap.  It will squeeze to nothing.  I have a picture of it and where it was applied, but the site still not allowing photos to load.  The pan gaskets were  installed dry as well.  Just a tiny bit of RTV in the corners where the gaskets meet.