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Rear Main Seal - Can't get crank to drop
#1355385 Wed Apr 15 2020 06:42 PM
Joined: Jan 2003
Posts: 303
H
Shop Shark
I decided while I was doing some other work to see if a new rope seal would slow down the rear main leak. There was a neoprene seal that had been leaking for several years. I removed it and cleaned up the surface of the crank under the old seal with 600 grit paper and flushed it with carb cleaner. I have a new Best Gasket rope seal to install. I plan to pick up a Sneaky Pete tool tomorrow. I've loosened the other main bearings 1-2 turns but I can't get the crank to drop any at all even with prying. Any suggestions? Looks to be difficult to get the new seal started without a little extra clearance. How much can it move without damaging the front seal and the transmission input seal?


Harold Wilson
41 Chevy 3/4 Ton
Re: Rear Main Seal - Can't get crank to drop
Harold41 #1355389 Wed Apr 15 2020 07:00 PM
Joined: May 2015
Posts: 2,784
Housekeeping (Moderator) Making a Stovebolt Bed & Paint and Body Shop Forums
If the rod caps are still installed, you'll just have to pry harder to overcome the piston ring resistance. 1-2 turns on the main bearing bolts isn't really that much.
If you loosen the rod caps too, you should be able to get it to move.


Kevin
First car '29 Ford Special Coupe
#2 - '29 Ford pickup restored from the ground up.
Newest Project - 51 Chevy 3100 work truck. Photos [flickr.com]
Busting rust since the mid-60's
Re: Rear Main Seal - Can't get crank to drop
Harold41 #1355391 Wed Apr 15 2020 07:02 PM
Joined: Feb 2004
Posts: 21,018
H
Boltergeist
Loosen or remove the transmission-to-bellhousing bolts. You might need to move the transmission back a little to let the bearing retainer clear the hole in the bellhousing. The crank can drop quite a bit at the rear without damaging the timing cover seal. I'd loosen the main bearing bolts 1/4" or so.
Jerry


The murder victim was drowned in a bathtub full of Rice Krispies and milk.
The coroner blamed the crime on a cereal killer!

Cringe and wail in fear, Eloi- - - - -we Morlocks are on the hunt!
Re: Rear Main Seal - Can't get crank to drop
Harold41 #1355399 Wed Apr 15 2020 07:30 PM
Joined: May 2015
Posts: 2,784
Housekeeping (Moderator) Making a Stovebolt Bed & Paint and Body Shop Forums
I forgot about the transmission input shaft. That would restrict it from dropping down.


Kevin
First car '29 Ford Special Coupe
#2 - '29 Ford pickup restored from the ground up.
Newest Project - 51 Chevy 3100 work truck. Photos [flickr.com]
Busting rust since the mid-60's
Re: Rear Main Seal - Can't get crank to drop
Harold41 #1355406 Wed Apr 15 2020 07:47 PM
Joined: Jan 2003
Posts: 303
H
Shop Shark
Thanks, I knew there was something I was missing.


Harold Wilson
41 Chevy 3/4 Ton
Re: Rear Main Seal - Can't get crank to drop
Harold41 #1355443 Thu Apr 16 2020 12:07 AM
Joined: Jun 2001
Posts: 730
T
Bondo Artiste
I’ve done this job on my GMC 270. In my honest opinion it’s best to lower crank even from front to rear. I removed the radiator, crank pulley, dropped torque tube, and removed the transmission. Then it’s very easy to lower crank and remove the rear main seal. I also used the best gasket brand rope seal. Pack as much of it as possible in the block side to make sure it’s fat in the block, to make as much contact with the crank shaft surface as possible. Same on the bearing cap side. I used RTV lightly on both the bearing cap and block surface. I snugged it down tight. I let it sit overnight and then raised the crank back up the next day, torqued the caps and then put it all back together. Little to no leaks.


Phillip
1927 Chevy Capital 1 Ton truck - basket case
1941 Chevy Suburban - Parts only
1949 GMC Suburban - 10 year project
1945 GMC half ton truck - Driver
1946 Chevy COE - Might restore one day...
1959 GMC Half ton long bed NAPCO

https://photos.google.com/u/1/albums
Re: Rear Main Seal - Can't get crank to drop
Harold41 #1355693 Fri Apr 17 2020 02:00 PM
Joined: Dec 2017
Posts: 808
D
Shop Shark
You should be able to get the top part of the neoprene seal out without dropping the crank. Have you tried pushing on one end to see if it will rotate out? Just asking, because a lot of the guys here seem to be inclined to replace the better two piece neoprene seal with a new rope seal.

Was the neoprene seal leaking because it was installed in a motor that was not machined for a two piece seal? For example, the 56 235 was the first year for the neoprene seal and the 55 and earlier blocks cannot be retrofitted because the machining on the rear main cap is too deep for the two piece seal and so you have to use a rope seal.

The other thing is that the rope seals of yesterday had an asbestos component to them. Today’s rope seals are a fiberglass graphite and do not work as well and are prone to leaking themselves. Not every Installation mind you, but quite a few.

If your block is machined to accept the two piece seal, which is an improvement by the way which is why gm switched over, why are you going back to a rope seal? No criticism here mind you, just couriosity.


Mike
Re: Rear Main Seal - Can't get crank to drop
Harold41 #1355724 Fri Apr 17 2020 04:32 PM
Joined: Mar 2014
Posts: 1,656
J
Shop Shark
It seems Mike above is suggesting the neoprene seal is better and if that's what he's saying I agree with him 100%. I found some very old rear main seals in the attic last year, but I'm not sure they'd still be ok to use. They've been there over 35 years. I think they're the old asbestos fiber seals, but I'm not 100% positive. They would have been bought in 1977. I used the neoprene seal in mine...when I got the engine there was no evidence it had ever been disassembled and it had a neoprene seal when I took it all apart. It also showed evidence of leaking, so I compared the seal I removed from it with a brand new one. You can see what I found in the attached image. The edge on the new one sticks out 1.1mm further than the old worn one, so it shows this seal wears out over time. Was that enough to let it leak? I'm certain it was. Here is what I did and it has worked for me:
1. I cleaned up the crank area which rides on the seal with 600 followed by 1000 grit sandpaper until it was nice and smooth.
2. I cut strips of self-adhesive foil tape until I could tell the thickness was going to push the seal out of the groove by .006~.008. This as I recall was two strips laminated on each other. I wanted to be sure the new seal made decent contact with the crank surface. Using a 1/2" piece of common copy paper (.004" thick) I could tell the new neoprene seal didn't fit quite closely enough without shimming it a bit. In other words, that piece of paper didn't have much resistance.
3. I cleaned the back side of the new neoprene seal and applied those strips carefully to just the bottom part...not the part on the sides of the seal. Then I checked to be sure the metal rod inside that neoprene seal wasn't going to be sticking out too far now. Turned out I needed to grind a tiny bit off both ends of one seal piece using a Dremel tool and a very small bit.
4. Then I assembled applying some aviation gasket sealer to the part of the seal that fits in the groove. No leaks now.

Attached Files
rearmainendtoend.jpg (13.47 KB, 109 downloads)

Jon

1952 1/2 ton with 1959 235
T5 with 3.07 rear end
Re: Rear Main Seal - Can't get crank to drop
Harold41 #1355725 Fri Apr 17 2020 04:37 PM
Joined: Mar 2014
Posts: 1,656
J
Shop Shark
Oh and one other thing that hasn't been mentioned yet but I think should be said: the better your main bearings are (the less slop they have), the better job your rear main seal will do. Oil is going to be coming out there in all conditions but less is better than more and the 235 leans back at a pretty good angle, you know.


Jon

1952 1/2 ton with 1959 235
T5 with 3.07 rear end
Re: Rear Main Seal - Can't get crank to drop
Harold41 #1355730 Fri Apr 17 2020 04:48 PM
Joined: Feb 2004
Posts: 21,018
H
Boltergeist
The full circle seal I suggested has a lip that will accommodate a "Speedy Sleeve". The specifications on the seal state that it will expand up to .015" oversize from its nominal diameter of 3 7/8". A worn crankshaft seal surface that does not give the rear seal a smooth area to run on could probably benefit from a repair sleeve, which is stainless steel, and far more wear-resistant than the original crankshaft material, IMHO.
Jerry


The murder victim was drowned in a bathtub full of Rice Krispies and milk.
The coroner blamed the crime on a cereal killer!

Cringe and wail in fear, Eloi- - - - -we Morlocks are on the hunt!
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