Rear Main Seal Leaking

[jmfurgason]

Has anyone used a liquid sealant for the rear main seal leaks? would you reccomend a sealant? the only option is labor intensive. Thanks JF

[ilvracn]

i never heard of a liquid sealant for rear main seals. if your talking about the type that you add to the oil, it works by softening the rubber of the seal. the v-6 engine in our trucks had a rope seal from the factory. there used to be a replacement seal that is a lip seal, they are no longer available. the addtive might slow down the leak on the lip seal but will do nothing for the rope seal.

[James]

Part number for the rope seal is: BS40048
Can be found on ebay and other places: https://www.google.com/search?q=BS40...hrome&ie=UTF-8

You will need this tool: Lisle 27000 Sneaky Pete Tool: Lisle 27000 Sneaky Pete Tool
Can be found on Amazon and other places.
https://www.google.com/search?q=lisl...hrome&ie=UTF-8

I don't have the part number for the rubber lip seal. Some else might have that.

Here is a video on an engine build. In it he talk about the rope seal at about 17 minutes into the video. https://www.youtube.com/watch?v=Ieckq771rDU

Hope this help.

[jmfurgason]

james & ilvracn thanks for the info, appreciate the responce. The leak is not awful yet just daily drops. Blue Devil was refered to me me, Iwas not up on this product, so thanks alot for your help. JM

[tbucketnut]

Hello guys, I have done many rope seals in my 64 years. If you can get a rubber lip seal then purchase it from Best Gasket, the best out there IMHO. However, to my knowledge not available for our Big Block GMCs.
Next best thing and really only other choice to me is to pick up the phone and call Olson Gasket: https://www.olsonsgaskets.com/
These guys have rope seals available in bulk and of a material superior to anything available in any other gasket kit. I will absolutely not use the rope seals in the felpro kit. They are complete junk and will be a leaker, in my opinion. Thank you have a great day.

[Prowbar]

Originally Posted by tbucketnut

Hello guys, I have done many rope seals in my 64 years. If you can get a rubber lip seal then purchase it from Best Gasket, the best out there IMHO. However, to my knowledge not available for our Big Block GMCs.
Next best thing and really only other choice to me is to pick up the phone and call Olson Gasket: https://www.olsonsgaskets.com/
These guys have rope seals available in bulk and of a material superior to anything available in any other gasket kit. I will absolutely not use the rope seals in the felpro kit. They are complete junk and will be a leaker, in my opinion. Thank you have a great day.

I'm curious, did you have a bad experience with the Felpro rear main seal kit for the GMC V6?

[tbucketnut]

Prowbar,
I will share with you my experience in the last four rebuilds which I have done in the last two years. These engines were for a 1954 Chev 235, a 1956 Chev 235, a 1962 Chev 261 all inline stovebolt 6 cylinders, and the fourth is a GMC 305 V6 C engine.

The first engine I worked on was the 1956 engine that was originally assembled by me in 2015. This engine had the felpro rope seal, and it began leaking immediately after assembly. Now it didn't leak bad but it would have a teaspoon of oil on the floor after each drive cycle. This is when I contacted Olson Gasket which happens to be the next town down from me. They are known for putting together obsolete gaskets sets for antique cars and tractors, many which are remade by original stencils of original sets. Through speaks with them and many visits to their small factory, I was schooled up on the newer materials that big gaskets companies are using are not like the original asbestos type rope seals, but another material used that does not work near as well as far as sealing qualities. Like I said this engine originally had a felpro rope seal in it that was assembled by myself in 2015 and leaked badly immediately after startup - I resealed with a 2 piece lip style seal made by best gasket in 2020 and is completely drip free to this day and this engine now rests in a 1952 Chev five window truck that is owned by a good friend.
The second engine had a different rear main cap because it is a 1954 235 and only a rope seal will work on that. I assembled that engine with a special rope seal material provided by Olson gasket and threw the felpro one away. This engine was also assembled in 2020 and resides between the fenders of a 1946 Chev Fleetline, it too is leak free.
The third engine was the 261 and I used the Best gasket two piece lip seal and I have that in my 1953 Chev 5 window truck with many thousand miles on it and the garage floor is drip free.
The GMC V6 I'm in the process of assembling right now and have aquired the special rope seal from Olson gaskets and will be using it. My intention is to post up some pictures in the next week or so showing the difference on the felpro rope seal versus the olson rope seal. For others to see for themselves and also to document my build for this engine that is going into my 64 GMC 1/2 ton.

Thanks for your comment,

Steve

[MoscowMule]

Thank you for the insight on the felpro rear main seal.I hope to be getting our 305 back from machine shop soon.I have gasket sets.However I need the camshaft cover gaske still.I was told by lizziemeister'sV6 about Olson. Gasket .I will be ordering a rear main seal it seems too.

[Prowbar]

Steve, thank you very much and I understand it completely now. On the 478 engine I'm putting together I used the Felpro kit. Can't say I was very satisfied with the rope seal kit. I'll probably pull it apart and redo the rope seal.

Could you tell me which type/diameter rope you ordered from Olsen?