The Stovebolt Site Forums The Shop Area Engine Shop Rear Main Seal

Has anyone used a Best Gasket 4519S, Rear main Seal for a 235/261. The 1960 235 I'm putting together has a rubber style seal factory setup.

I have not. But I have pondered the same question.

FYI - NOS GM versions of the rubber rear main (and NOS crosses to other manufacturers) are NOT hard to find on eBay. IIRC, there’s an OMC version of the same seal that is pretty widely available.

Generally speaking, when it comes to rubber parts, I look for NOS whenever possible. Old rubber formulations seem to be borderline eternal. New rubber starts going bad before it’s even removed from its box.

That approach has served me pretty well with things like suspension bushings, motor mounts, etc. But I’m not sure how transferable it would be to something like a rear main.

Seems that a NOS rear seal isn't rubber, it's Unatainium ...

I don't think I'd try using a NOS rear main seal, anyway. Depending on storage conditions for 60+ years, it's likely to be hard and brittle.

I don’t know that I’d try it either, but I’ve been amazed at how long older rubber can stay supple.

I’d bet it’s not as brittle as one might guess.

Craig - if you’re hard up for entertainment, here’s a list of crossover numbers from RockAuto’s listing for a 235 rear seal. Use them to search EBay if you wish.

If you find one of these seals made by Fel-Pro my experience is it will not be hard and brittle no matter the age. I have some I've saved for 50+ years by the way and they are still just like new. I have been told GM did not make this seal but outsourced it. Around 1999~2000 I spoke with one of the Fel-Pro engineers who had been on the team who had developed that seal. He said while it was commonly referred to as a neoprene seal it wasn't exactly that. He said it was a proprietary blend of compounds he couldn't discuss. We also talked about the practice of offsetting the two pieces by rotating one a bit in the channel. He paused and said something like "well as long as you don't exceed the offset about 1/16" it probably won't hurt." He added "I wish I could say that's a good idea but we don't suggest it because our research showed it was not necessary and we could not control how much people would rotate the seals." He said if you just follow the instructions on the seal package all will be okay. He added that seal had been designed to work on a nice smooth surface within a specific crank to bearing clearance and .001" would be ideal. I asked about a worn crank with a clearance of say .003". He said "you're on the outer edge of good practice there unless you are using a one-piece spring lip seal (which was never made for the 235)". He ended by saying he was less than a month away from retirement. Nice guy and very interesting. I was impressed he took as much time to discuss it as he did.

I would suggest doing this: install the right Speedi-Sleeve using red Loctite where your crank meets the seal. If you just have your crank polished where it meets the seal, then add some shims behind the seal piece until you can not draw a 1 inch piece of common copy machine paper out without it tearing. Unless you did the machining, you don't know how much metal was removed. You can use foil HVAC tape cut into long thin pieces if you need shims. Each piece should add about .004". Also no crank that was mated with a rope seal I've seen in the last 60+ years has had a smooth enough surface for the rubber type seal. Any roughness will wear that seal out tout de suite. I have images of some I've saved but I'm not where I can access them now. Dealerships commonly installed this seal when they could because they could do it without removing the engine. Often they failed pretty soon.

As for Best Gaskets, I don't know what they're made of and I think they're absurdly overpriced. Personally...I'd look for a genuine unused Fel-Pro seal if it were me. Get one made by the company who engineered them and not by somebody who just copied them. Good luck!

No matter how good the two piece seal happens to be, do yourself a big favor and get the block machined for a Timken 417210 one piece lip seal, or the equivalent made by some other manufacturer- - - -Outside diameter 4 3/4", ID 3 7/8", thickness 3/8",double lip seal with a garter spring. It will also work with a speedy sleeve, since the garter spring can accommodate a .015" +/- shaft diameter.

If you want to load up your block and bring it to Townsend this year, I'll be glad to machine it for you. I offered to do a demo of the procedure at last year's show, but the promoter shot the idea down. This time, I'm planning to ignore anybody else, and machine somebody's block, even if I have to do it off site with an extension cord from someone's motel room, or a generator. I'll probably be bringing one of my own blocks, as I plan to build several engines with that type of seal in the near future.

www.ebay.com/itm/116927189289?

Jerry

We used the Best Gasket seal when we built John's 261 in Charlie, about 6-7 years ago. So far, no leaks, I'm pretty sure. I made a seal installation tool from an old piston to pack it firmly into the block and the main bearing cap, which is something most people don't do.
Jerry

I've used a lot of the Best Gasket rope type seals, not one has ever leaked. It's nothing like the seals that come in the gaskets sets these days. The first one I ever installed was packed in like like the old Fel-Pro gaskets were, I followed the service manual procedure. The engine was a 462 cubic inch V8. It ran for a 20 minute break-in and a little while longer for the tune up checked. I shut it down and tried to restart it, no go, locked up solid! I put it in the garage frustrated, next day it fired right up and ran, it would not turn over again when hot. I pulled the pan and rear seal out, I found the rear of the crank was hot with a thermo-heat gun, that's why I pulled the seal. I installed another Best Gasket seal but followed their instructions, this time it worked like a charm, never leaked and never got hot again.

When installing them now, I use the crankshaft to seat the seal. I install the seal in the block then set the crank in in place and take a soft rubber hammer and whack it a few good times to form the seal. Take the crank back out, carefully remove the seal, add the second piece and repeat. The first piece goes into the cap, trim the ends just a Best suggests and don't add oil, grease, or sealer to the seal surface.

Just in case anyone is hunting for an original FEL-PRO 2 piece rubber (neoprene, whatever - lol) seal, I found this older 1928-80 FEL-PRO Parts Catalog on the interweb. It lists the FEL-PRO # "BS 13363" as their back then part number for the seal for both the 235 (1955-63 - their designation) and 261 applications from 1954-62. Oddly their catalog lumped Chevrolet and GMC trucks together under the "GMC Truck" category.

The link is a great potential source for identifying old FEL-PRO part numbers if you're hunting some no longer offered products.

Best of luck Craig in tracking your seal down.

This going in a 1960 235, it is not machined to use a rope type seal. JW51 sent me a link to NOS McCord rear seal on Ebay, it's $22.00 plus shipping. Has anyone used on of these?

https://www.ebay.com/itm/2568992339...r=&widget_ver=artemis&media=MORE

Either style of block can be machined for the full circle seal, not just the one with the rope. Cutting the counterbore for the lip seal takes the original shape out completely.
Jerry

Craig I've not used one of those sold under that brand however there may be a link and it is possible both were made by the same outfit. Federal-Mogul owns Fel-Pro and at one time also owned McCord and may still own them. I'd say the price looks okay (given what people are asking for a seal that ought to cost less than $10).

I think I'll pull the trigger on the McCord gasket, may even get an extra. ... Jerry, I have the 261 that would be a good candidate for your one piece rear seal conversion. I could bring the bare block and main caps to Townsend.

OK, glad to help if I can. I'm also considering bringing a junk block to demonstrate the preliminary work to convert to the same size main bearings front to rear on stovebolt engines. That involves boring all the main bearing holes to the same diameter, and installing reducer sleeves to fit small block 400 main bearings. Then the downsized bearing bores are line-bored and the crankshaft is reground to SBC 400 main bearing diameter. That procedure also saves a "worn out" crankshaft.
Jerry