The Stovebolt Site Forums The Shop Area Engine Shop 261 Rear Main Seal Leak Fix

Hello everyone
I'm looking for tips on how I can best fix my rear main seal. Details:

I had a 261 engine rebuilt by a local race engine shop, and I am really enjoying it. Problem is, the rear main seal leaks. A LOT. So I am searching for the proper fix, as I do not want to do this again, and I know those old rope seals were problematic. I know a one-piece seal is not an option, but I am looking for any tips/tricks that would fix my problem.

Any guidance is greatly appreciated!

Sorry for the delay - I lost my post due to lightning-caused electricity loss (oddly, only in the wi-fi router room).
Most of my post got scrambled

Get a Best Gasket 6100 rear main seal.
"each kit includes installation instructions, a special knife, and a few other trimming aids."

Read this Tech Tip on Rear Main Seal Replacement.
Installation procedure on oldGMCtrucks.com - different gasket
Another article that mentions the Best Gasket Seal,

Maybe someone here can also find a good post describing installation?

Ditto on the Best Gasket seal- - - - -it's the closest thing available to the old OEM seal with asbestos fibers in it. Getting the upper half installed can be problematic, but with the low mileage on your engine, it won't be terribly hard to remove the leaky one. You'll need to loosen all the main bearing bolts a couple of turns and let the crankshaft drop down a little to make it easier to snake the upper seal rope into place with a piece of wire or the "Chinese handcuff" that the Lisle "Sneaky Pete" seal installer kit includes.
Jerry

If this is one of the later 261s, wouldn't it have been built with a neoprene seal?

Yes some 54 and all 55 and up 261s I believe will /can have a neoprene seal. I just finished a 261 rebuild and assembly myself, used the neoprene and it is dry as a bone under there, if you can use the rubber seal use it over the rope in my opinion.

"can" might be correct, but "will" is not assured: 0.137 Seal: graphite-impregnated 1940-1957 that Parts Manual was up to 1957.

I'll look that part number on the GM parts wiki and report on later 261s. I think I used a rubber seal on my 1960 261 that I rebuilt in 1972 (and, it is still running with no leak).

added later
GM/Chevrolet part #: 3836774 [correct code is 3835774]
I cannot find a "cross listed" modern part?

Jim Carter Truck Parts shows a variety of types/brands of 261 rear main seals

My 1954 261 uses the rope seal not a neoprene seal.
Get on Ebay and type in "Victor JV650" they're the original type of rope seal with asbestos fibers.
I believe they come in a blue and white box, I had no luck with today's type of rope seals.

Tim

good info, Tim, you come with anything else??

Yes - Chevs of the 40s - rubber rear main seal

I do not have access to a 1960-62 Parts Catalog

If you have a 60-63 catalog, please look in in group: 0.137 SEAL, Crankshaft Rear Bearing Oil

Group 0.137 SEAL, Crankshaft Rear Bearing & Cup Oil

Take you choice - both styles are listed.

NOS part #3812855 (see it listed at the link on the first line, above).

Make your choice, take your pick, keep your fingers crossed.

I found an old post here where I indicated /confirmed that the seal I used in my 1960 261 (in 1972) was the rubber-style seal. That engine is in my 1954 Suburban, and, it is not leaking, yet.

I used a neoprene seal in mine and here is what I did:
polish the rear main seal contact surface really well on the crank (this is a must)
using a piece of wax paper or dollar bill determine how well the rear seal contacts your crank when it is installed...you want to feel resistance on top and bottom.
shim as needed...I had to shim mine about .006 on top and bottom seal...strips cut from high quality foil duct seal tape is very good to use.
if you have to shim more than .006 use a Dremel tool to remove some of the metal core (rod) from the two seal pieces
lubricate with motor assembly oil

Also...be really careful to check your side cover gasket (push rod cover). These are known for leaking and when they do (anyone can fail to get them sealed correctly), the leak mimics the rear main seal leak almost exactly.

Good luck!

Just to further confuse this matter: the 1960 Chevrolet Truck Shop Manual describes the installation of the braided wick-style seal:
1. When replacing the seal in without removing the engine from the truck.
2. When completely rebuilding the engine out of the truck.

That rubber seal must have been a later "improvement" (substitute part)?

I'm happy to hear of another source for rear main seals. I have also learned that there is a source for the neoprene seals, which IIRC is Best also.

In fall 2017 I did an in-situ crank reseal on my '55 235 truck engine. It was leaking badly. I had a rope seal in the original Fel Pro box and did a trial fit on the main cap. I decided that there was no way I could roll it down with a hammer handle or anything else to make it fit the crank. I remember when I built the engine many years ago that after I had the rope seal installed I couldn't turn the crank. Don't remember what I did instead at that time but somewhere along the line I pulled the rope seal to replace it and couldn't get the new rope seal installed so I used the neoprene lip seal. Eventually it began to leak and soaked the clutch, which brings us to fall '17. I could not get a new neoprene seal. One of the suppliers told me that the tooling had worn out and there wasn't enough demand to warrant retooling. So, digging around in my parts boxes I found two NOS Fel Pro seals in boxes: one was a two-piece and one was a one-piece that you sort of roll into place. I used the two piece.

Of course, having the rear main cap off, I plasti-gauged the bearing and it was loose enough to flood the seal with more oil that it probably could handle so I bought a set of main and rod bearings and set the rear main as tight as I dared to minimize the oil flow. The engine had around 200,000 miles on it but the crank was still round enough to hold the bearings with a little shimming. This engine has pinned mains so I had to drop the crank with all the attendant hassles.

After all this, it still leaks, not as bad as before but it's not bone dry either. Engine is quiet and runs like a champ with 200k on the rings and pistons. I have a new side cover gasket so I'll replace that and see if the leak dries up but I'm not holding my breath.

BTW do not start this job outdoors in late October.

Good information in this thread, thank you for everyone's input. And I definitely won't be starting this outdoors in the fall

Too bad we didn't have a chance to machine that block for a full circle lip seal while it was in the process of getting rebuilt. I machined Cosmo's 261 for that seal at Homecoming earlier this year, after doing a practice cut on a scrap spray-oiler 235. He just got the engine assembled a few days ago, so there's no "running report" on how well it works yet!
Jerry