Rubber Rear Main Seal
 

I'm trying to reproduce New Rubber Rear Main Seal kits for the V6 and V12 engine.

In order to do this I am in need of 2 Rear Main Bearing Caps. 1 of these Rear main caps will be destroyed in the process of reverse engineering the seal. Since this is the case I don't want to borrow caps from engines that are in the process of being rebuilt. I would prefer to buy (or trade?) caps from junk blocks so that I'm not at risk of losing something that is irreplaceable.

Does anyone out there have junk blocks that we can steal the rear main cap out of?

Re: Rubber Rear Main Seal
 

I have some caps, I never look at this but I would love a rubber rear mail seal

Re: Rubber Rear Main Seal
 

Are any of the Rear Main Caps from Junk blocks? My manufacturer will end up destroying 1 of the caps (i.e. they cut it in half to measure the journal) in the process of reverse engineering the rubber rear main seal.
Feel free to give me a call at the shop, you can get the phone number on the Olson's Gaskets website.
Thanks,
Richard

Re: Rubber Rear Main Seal
 

Thanks Richard for your work on this. Ive been by to see you guys a couple times in the past. Appreciate everything you do to keep our hobby trucks on the road. Steve

Re: Rubber Rear Main Seal
 

What might be interesting to know is that a rubber rear main seal has been produced in the past. I just scored one on Ebay, they are new old stock.

The number is Detroit Gasket 17091 (there are more numbers, BS40048 is used also, but in conjunction with the rope seal)

This is a lip seal, consisting of two halves with a steel backing for rigidity. I'll upload some pictures later today. I'd be willing to help out with any info you may need, as a good rear main seal saves a lot of grief and oil soaked driveways.

Re: Rubber Rear Main Seal
 

Here are some pictures of the rear main seal.

Re: Rubber Rear Main Seal
 

The fel pro number is correct but it's a slim chance it's rubber, I've ordered 4 of the same number and I got lucky and one was rubber the rest are rope, I think it was a later design

Re: Rubber Rear Main Seal
 

I assume so too, when was the last time you ordered the rear main seal and got the lip seal?
Maybe they are discontinued, maybe not? I'll see if I can reach out to Fel Pro and ask them.

Re: Rubber Rear Main Seal
 

6 years ago

Re: Rubber Rear Main Seal
 

Yeah, that's a long time ago.

Just got off the phone with Fel Pro, the guy said they only stock the rope seal and denied the fact that the lip seals had the same part number, which clearly isn't true.
At least he could find the GMC V6 engine in his computer.
I'm assuming the lip seals have been discontinued. They still produce the rope seal, so if you order one, that's what you get (P.S. the rope seals from FelPro are crap...)

If OlsonsGaskets can produce a quality lip seal then everyone would benefit!

Re: Rubber Rear Main Seal
 

One thing I'm wondering about:
For the rope seal to be lubricated, the V6 crankshaft has angled serrations cut in the crankshaft. I added a picture that I had, it might be difficult to see because of the assembly lube.

Do these serrations interfere with the sealing capability of the lip seal?

Should one have to regrind the seal surface on the crank for the seal to work properly?

Re: Rubber Rear Main Seal
 

The way the serrations is made on the shaft, as the crankshaft rotate the serrations try to pull the excess oil back into the crankcase. And the rope seal works very well with this because it has a wide surface for the seal to work with.

The rubber seal (as I understand it) needs a smooth surface, just like the front seal has on the crankshaft hub. It only has a thin lip that make contact with the shaft.

I don't know if placing a rubber seal on a shaft with serrations would be any better or not. In my opinions I think the rope seal is better and the rubber seal. The rubber seal on the serrations could be more prone to leakage due to the serrations.

Re: Rubber Rear Main Seal
 

I found this listing on eBay, do they look correct?

https://www.ebay.com/itm/38723916898...mis&media=COPY

Re: Rubber Rear Main Seal
 

Yes, these are the right rear main seals. Take a look: https://www.finditparts.com/products...el-pro-bs40048
I have the Detroit 17091.

@63GMC4x4 did you regrind the sealing surface before installing the lip seal? Do you have any leakage?

Re: Rubber Rear Main Seal
 

Do these Rubber seals also come with the water absorbing pipe-cleaner looking side seals, used with the rope seal kit?


I have never done this before and was curious on the procedure.

https://www.youtube.com/watch?v=Ieck...bGR3zH&index=4

Whole procedure on the Rope seal type of installation starting around 16:54.

Re: Rubber Rear Main Seal
 

Mine did not come with anything other than the 2 seal halves. No instructions in or on the box either. Looking at the Fel Pro pictures of the same seal, it seems like it came with the gasket/rope type side seals and the 2 rubber plugs.

The seal installation like he did in the video is sloppy, you're supposed to trim the seal with a clean cut. The pipe cleaners are soaked in water and RTV is squeezed in to form the seal. The water helps it to cure.
Equally important to put a little bit of RTV/sealer between the main bearing cap halves to prevent any leakage.
The 2 plugs are installed to cap off 2 holes in the bearing cap or block, can't remember what the purpose of the holes is.

Re: Rubber Rear Main Seal
 

Guys, look at this. I wonder if a rear main seal off a Pontiac 301 would work:

http://www.wallaceracing.com/rear-ma...erchanges.html

Re: Rubber Rear Main Seal
 

Interesting, I looked at this also. Going by the interchangeability, the seal groove in the block and cap should have the same dimension as the Pontiac I'm assuming.

If the assumption is correct, the only variable is the GMC V6 journal diameter vs the Pontiac journal.

To get a dimension for the sealing journal on a Pontiac I found this:

https://www.tinindianperformance.com...ontiac-engine/

3 inch main journal: 3.188" inch sealing journal
3.25 inch main journal: 3.436" inch sealing journal

Can anyone measure the crank seal journal diameter of the GMC V6? Don't have one apart to check right now.

Re: Rubber Rear Main Seal
 

I tried to look it up, but the service manual only gives the O.D. of the rear main bearing journal, which is 3.1239". It may be the same diameter where the seal rides.

Most Pontiac V-8's also used a rope rear main seal. I am rebuilding a Pontiac 326 for my cousin as we speak and can verify!. The 301 was a real oddball, most everything about it is different compared to older Pontiacs.

Re: Rubber Rear Main Seal
 

Looking at this Ebay listing I would say it is correct for the GMC V6. I can't be 100% sure without holding them in my hand. Also what is not clear to me is if these are new product or if they are old stock. I don't need to reinvent the wheel if this dealer has already got the solution. Will have to do some checking here.

Regarding Felpro BS40048: At some point 5 to 10 years ago they switched from rubber to rope and kept the part number the same. I got burned by that. Now BS40048 is discountinued altogether. So if you're trying to source an old Felpro set through Ebay it's a crap shoot as to whether you'll get a rope set or rubber set. A really old superceded Felpro part number for the original rope seal with cylinder block plugs and wedge shaped side caps was BS12946.

To my knowledge there is no one producing the round rubber cylinder block plugs that was originally provided in these rear main seal kits. I still provide these in my rope rear main seal kits because I've junked out a lot of old sets but my supply is running low. What I need to know is does the plug need to be designed exactly like the originals with the concave divot on one side or could I just produce a slightly thinner plug without the divot? Anyone out there with insight into this?
Thanks

Re: Rubber Rear Main Seal
 

Had a little time today to look into this Ebay posting. Looks like I was a little too hasty in my previous post. I sincerely doubt this will work (see picture for comparison).

Under "Item Specifics" of the Ebay listing it gives a manufacturer part number of RS29025 which is ROL brand. The interchange that they list is BS30136 (Felpro) and JV723P (Victor). I recognized these as the Ford V8 260, 289, 302 ci rear main seal. I have a BS30136 on the shelf so I thought I would compare.

Here's what I found. The Ford is much larger over all, however it has a thinner width .230" compared to the GMC seal which has a .290" width.

FYI. The old Victor part number for the rubber seal is JV616. I looked back in my Victor catalogs and this Part number doesn't appear until 1973. It appears prior to 1973 only the rope (Victor p/n JV716) was available, but the rubber should work retroactively for earlier engines.

Re: Rubber Rear Main Seal
 

What you say makes sense, when I rebuilt my 351 20 years ago I bought a FelPro full gasket set, and it included a 2 piece rubber lip seal and the wedge type soak in oil side seals. I do have a later issue FelPro BS40048 and it's a rope seal with pipe cleaners and a small tube of silicone.

As far as the round rubber plugs are concerned, all they really do is provide a smooth surface for the oil pan gasket where it goes over the holes for the rear main bearing cap bolts. The concave side goes towards the bolt heads, my guess is they made them like that because the bolt heads are not exact so the plugs would conform a bit to be the right height. I think you would be fine making the plugs flat, it they are a bit too low add a bit of silicone, if too high just shave them off with a razor blade.

Thanks for making the effort to furnish gaskets and seals for these old engines!

Re: Rubber Rear Main Seal
 

[QUOTE=OlsonsGaskets;78214]Had a little time today to look into this Ebay posting. Looks like I was a little too hasty in my previous post. I sincerely doubt this will work (see picture for comparison).

I actually bought that from eBay that posted to try it out , i pulled out my original one in my 401 this morning it was a rubber one and it's stamped GMC on it. I should have taken a picture to compare the two before I installed it and match it up to this one from eBay and it's exactly the same. I installed it this morning. Fit perfectly!

Re: Rubber Rear Main Seal
 

It is the correct seal, looks new old stock, I remove my GMC sale and held it up next to it. Exactly the same size so I installed it installed it this morning fit perfectly! It came in a bag and it said 17091 on the bag and I also confirmed with the seller before I purchased it. He confirmed it is the correct Seal and had about 10 of them left

Re: Rubber Rear Main Seal
 

[QUOTE=63gmc4x4;78220]Good to hear that it fits! Was the sealing surface left stock on your 401? (i.e. with the serrations?)

@Olsonsgaskets I believe the plugs is concave to clear the 12 point bolt head. Suppose you could make them a little shorter to cut down production costs.

If you need any measurements of the NOS rubber seal (17091) that I posted pictures of, contact me.

Re: Rubber Rear Main Seal
 

[QUOTE=Prowbar;78222]Yes very light, but looks like the old seal was sealing just fine!