1941 Cadillac rear main rope seal replacement with motor in car

[41coupe]

Here is my question: Has anyone replaced the rear main rope seal on the 346 c.i. Cadillac motor, with the motor in the car? I have all the parts to do the job, including a "sneaky Pete" tool, and read some suggestions on "tricks" to make the job a little easier. I watched videos on installing the rope seal with the motor apart on the work bench, but I wonder if it can really be accomplished working under the car. Will I be creating more oil leaks, or does it actually work?  Phil   

[39LaSalleDriver]

When I first got my LaSalle it had a leak from the rear main. It would drop at least a fifty cent piece size puddle within a couple of minutes so I decided it was one of the first things I needed to tend to. Lacking the experience and/or confidence to do the job myself I paid a local garage to do the job for me and provided all the instructions on how to do it and provided a new seal. It still leaks...Admittedly, not nearly as bad, but it still marks it's territory wherever I go.

Was it worth the few hundred bucks I paid to have the job done? I don't know...possibly. Did the shop even do the job or just take my money, tighten a couple of bolts and throw my new seal in the trash? I don't know.

If I were to do it all over again with the tools and experience I have now, I would likely take on the job myself but it's nowhere on my priority list at this time. I've just learned to live with the drip and keep an oil mat under the car.

Obviously, if the engine is out and you have full access to replace it I would think it better. But by all means if you feel good about doing the job in situ, give it a try. Just be aware that from what I can tell in reading other people's experiences and based on my own direct experience, it's going to be a crap shoot as to whether it fully solves the problem or not.

[Poncholover]

The modern graphite rope seals just do not work as well as the old asbestos rope did.
There are some modern alternatives but the magic bullet for many is to retrofit a 2 piece rubber seal.
Maybe it is possible to find one that could work in this application?
What a step forward this would be!

[jackworstell]

I understand that there is a modern molded seal that will work on 346 ci Cadillac flatheads
( except maybe the first rew years were "slinger types not meant for seals )

...See attachment.
I guess it is a Mercedes part
----------------------------------------------------------------------------------------------------
I have only tried this once....many years ago on a 460 ci out of a 1978 Lincoln
It was a job.   The main bearing caps and the connecting rod caps are have to be loosen

Getting the lower half of the rope seal out wasn't hard.

Getting the upper half out was tough....it wouldn't come out in one piece
It came out a piece at a time and also portions got stuck up in the seal grove
I finally cut off a section of speedometer cable...stuck it a drill
....and used this get get the remaining "stuck" pieces out.
It was slow going.
So far as I could tell the rotating speedometer shaft piece didn't damage any
of the machined surfaces


As I recall  getting the new rope seal back in wasn't easy but I finally got it
----------------------------------------------------------------------------------------------------
So can you do it ?  My guess is that you can.  if you have plenty of patience
and time. It's not as easy as it looks

By the way...I don't know when the 346 ci engines switched from slinger to rope seal
...our  1937 seris 60 has the slinger.
What year do you have

[fishnjim]

Won't know til U try.
Another one of those dying arts for auto mechanics.   They weren't made/anticipated to last this long either.   That's an octagenarian motor.
We still use rope type seals in industry, but there's so many kinds now, it's not easy to quantify.   
The main thing I learned over the years was the shaft and sealing surfaces have to be in good shape.   If there's any grooving, it has to be taken out and resurfaced.   One of my engineers was complaining about his horizontal reactor shaft leaking, kept adding packing, retightening, etc. and when we opened the unit and pulled out the shaft is was chewed up pretty bad.   Material and worn out packing gets in there and acts like abrasive and wears a groove where the seal is supposed to seat.   Worked flawless after repairs, but we had to institute regular inspection/repair intervals.   
No kind/type of seal will seal against that.   The seal surface has to be flat and running true.   So you need to check the run out to make sure it's nto a bearing/bushing issue at the root cause.   Any machine shop can build up and cut back to spec. but that means you have to remove and tear down.   You won't know that until you get in there - unfortunately.   
I suspect that's what's going on with that other guys slow leak.   Sealing these old engines is an issue and why I recommend to run them on the dyno or engine stad before they get reinstalled.   The modern sealants, etc. can cure them if the rebuilder knows his trade.

[z3skybolt]

I purchased my current 1940 LaSalle 5019 earlier this spring.  Before purchase the owner agreed to replace the leaking rear main seal.  He had a local mechanic, in Midland MI. who was familiar with the process, completer the repair..  Said it was no bid deal.  Did it of course without removing the engine. Stopped the leak.  900 miles later still not dripping.  Who knows about the next 1000 miles however.

Bob R.

[harry s]

There's been a lot of discussion on this subject previously on this forum. Do a forum search for "Mercedes seal". Given the amount of trouble to pull the engine just for the rear main seal I would be tempted to give the Sneaky Pete a shot.     Harry

[wheikkila]

pulling the pan is easy. And not a bad thing to do. You will be able to clean out of the sediment in the bottom. Now for replacing the rope seal. You can loosen the other two mains because you will have pulled the rear main. This will help to pull the old seal out and the new seal in. On the rear main there are two seals one on each side. Make sure you change them also. Make sure you don't undercut the seal. You will also want to put a small amount of sealant between the rope seals and the side seals. I have changed many of these and not had a problem with them leaking. Just take your time. Be sure to ware something that can get oily and safety glasses. you don't want oil in your eyes. If you have and questions please pm me.
            Thanks Wayne   

[jackworstell]

ERROR

In my previous post I said the rod bearing caps had to be loosened to do this repair
My mistake...just the main bearing caps have to be loosened

Curious...how many of you have sucessfully donne'this repair
( on any engine using a rope rear crankshaft seal )  ?

Jack Worstell

[Joe Jensen]

I replaced the rope seal on my 1949 series 62.  I used a lip seal to replace the old rope seal.  However it is leaking on me again (not as bad but still leaking).  I looked back through pictures and there appears to be some buildup (corrosion?) on the crankshaft jounal where the seal contacts that I failed to notice at the time.  I will probably need to remove the whole cranshaft to get this fixed right.

There is an excellent write up that was done in the '49 Time news letter that I followed.  I would expect there would be similarities to your flat head.

http://www.1949cadillac.com/stopping-an-oil-leak-update/

Good luck!
Joe Jensen

[Eric Voigt]

I tried several times, damaged several rope seals and two sneaky Pete's.  We loosened the rods and mains and no joy, finally pulled the engine and did the repair.  Good to go.

Don't waste your time, pull the engine, bolt it to a a stand and replace it.

[The Tassie Devil(le)]

The trouble with loosening the main bearing caps to try and gain crankshaft movement is negated by the transmission and front seal and timing chain stopping the vertical movement of said crank.

Bruce.

[Roger Zimmermann]

Even if the crankshaft is going down a bit, the distance between block and journal will not increase dramatically. Don't ask why I know that...

[Jay Friedman]

I've never done this on a 346 flathead motor.  I have done it 3 times along with another guy on 331 1949 and 1951 OHV motors with the motor in the car.  It is best done as a 2-person job. 

On 2 of the motors we loosened the main bearing caps to help get out the old rope seal; on one motor it was not necessary.  (Loosening the main bearing caps on a 331 does lower the crankshaft a few thousandths of an inch, which slightly eases pressure on the rope seal.)  To get out the rope seal we screwed a wood screw part way into one side of the rope seal, pulled on the screw head with pliers while pushing on the other side with a flat rod.  We replaced the rope seal with a modern neoprene seal obtained from Terrill Machine in Texas.  The neoprene seal must be installed in the correct orientation to prevent leaks.

As Joe Jensen wrote, Art Gardner, with whom I collaborated with on 2 of these jobs, wrote this up.

[41coupe]

Thanks to all for your comments. I think I might try to change the rope seal, if after I inspect and clean the pan, I'll make the decision. My current philosophy is, "it is only dripping a small amount", so maybe I should just live with it. I have owned the Cadillac since 2013, and it hasn't gotten any worse over the years. I'll keep you posted on what I decided. Probably start working on it in a day or two.  Phil

[LaSalle5019]

A lot of good comments in this thread. I will add one comment related to the two side seals on the rear main bearing. When my engine was rebuilt I used the Best Gasket kit but eliminated the two cork seals that go along side the rear main bearing cap/seal housing. Cork is okay but I wanted to eliminate two potential leak paths. Instead, I filled the void with Permatex The Right Stuff.  Stuck the nozzle down the square slot and filled it up to the top.....you can see it fill the void.  It worked great. Parts will need to be clean and oil free. Good luck with whatever you decide.