News:

Due to a technical issue, some recently uploaded pictures have been lost. We are investigating why this happened but the issue has been resolved so that future uploads should be safe.  You can also Modify your post (MORE...) and re-upload the pictures in your post.

Main Menu

rear main seal

Started by alzink, August 19, 2021, 01:35:15 PM

Previous topic - Next topic

0 Members and 1 Guest are viewing this topic.

alzink

The rear seal in my 390 is leaking more as time goes on. A local mechanic believes that after backing off the transmission  the engine pan can be dropped and after backing off on the crank bearings the seal can be replaced by pulling down the pistons. Just wondering if anyone might have experience replacing the rear main seal in this or other manner with the engine in place.
Thanks

Daryl Chesterman

Not sure what year your 390 is, but on a 1959 it is unnecessary to disconnect the transmission.  Just drop the pan, remove the windage tray, remove the oil pump, and rear main bearing cap.  From there, the rest of the R & R of the rear seal may be easy or difficult, depending on how difficult the upper half of the seal is to remove.  Not knowing the repair history or mileage on the engine, you might want to consider rebuilding the oil pump while it is removed.

Daryl Chesterman

Jay Friedman

I've never worked on a 390, but have done this 3 times on similar 331s ('49, '51).  I agree with Darrell.  To add to what he wrote:

1. You won't have to touch the pistons.  Instead, a good idea is to loosen the 3 middle main bearing caps somewhat, which with the rear main cap removed will result in the crankshaft dropping a few thousands, which will in turn lessen the pressure on the top half of the old seal;

2. Assuming the old seal is a rope type seal, to remove it screw a small wood screw into one side of it part way.  Then using a brass punch so as not to scratch the crankshaft journal, push the other side of the top half of the seal with the punch, while at the same time you pull on the screw head with a pair of pliers. 

3. Buy a replacement neoprene rubber seal from Terrill Machine, DeLeon, Texas rather than an inferior original type rope seal.  The neoprene seal not only lasts longer, but is easier to install since you don't have to trim it.  You just push it in, making sure it is facing the right way according to the instructions that come with it.

Besides rebuilding the oil pump as Darrell suggested, if time permits you might want to check the bearing clearances with Plasti-Gage. 
1949 Cadillac 6107 Club Coupe
1932 Ford V8 Phaeton (restored, not a rod).  Sold
Decatur, Georgia
CLC # 3210, since 1984
"If it won't work, get a bigger hammer."

Andrew Trout

A tip that came up when assembling my 390 was to slightly offset the edge of the seal from the block, so that the surfaces of the seal, the block, and the rear main cap weren't flush all with each other. I did not do that, but it certainly makes sense to help reduce the chances of a leak in the future.

Rochester, NY
1961 Convertible

fishnjim

If the surface where the seal seats is damaged,(grooved, etc) then crank will have to come out and go to machine shop or it'll just leak again, otherwise, a seal replace.  Ditch the rope if you can as noted unless the mechanic is skilled with it.
We've had people try this (rope) and then ask after, how to do it, so kudos for planning the job.   Some have done and still leaks, so inspect the seating surface!   
Historically, it's one of those damned if you do, damned if you don't things, and generally gets left undone too long, and makes matters worse/causes damage necessitates repair on its schedule not the owners.   
I guess one needs to assess if it's time for more engine maintenance on it while it's down.   ie, time to bite the rebuild bullet?   Seals usually go because the shaft they're sealing starts to move(bearing wear) and "wallows" out the seal material or seal material just wears down/ages/loses elasticity til it no longer adequately contacts and the liquid flows out.   

alzink

Thank you all!
I should have been more specific
The 390 is in my 1963 Cadillac Deville
From you'd suggestions I need to check for bearing wear, put in a new( rebuilt) oil pump any suggestions on new vs rebuilt, and use the Terrill rubber seal

I'm a bit surprised that I don't need to back off on the transmission, but Wonderful!

Thanks again.

russ austin

Fel Pro has the wrong seal, use Best gasket seal.
R.Austin