[Baba O'Riley]

Hello all, and happy three-day.

I've got a rear main seal on my '71 / 400 that has opened up badly -- my wife's new name for the car is "Exxon Valdez." I do some work on the car but I don't have the aptitude, tools and access to things like lifts that many of you do. So I'll be using a mechanic to do this RMS replacement. None of my usual mechs will warranty a RMS repair, which comes as no surprise to me since these cars are so leak-prone, but I wanted to ask you guys which would be the best way to go to minimize leaks there.

It's my understanding that the old rope / wick seals aren't as effective as they used to be because manufacturers aren't allowed to make them with asbestos anymore. Would a two-piece neoprene seal from Viton be a better way to go?

I'm also told that the one-piece seals, while more effective, often can't be used with the original crank and require an engine pull, which I'm trying to avoid. Is this true? (Mechanic says he can install a two-piece by simply pulling the oil pan and maybe dropping the crank.)

Thanks as always for your insights.

[kingbuzzo]

I had the same problem last year and also not mechanically inclined as most here.

My mechanic ordered the two piece BOP seal that is guaranteed not to leak if installed properly and of course it is still leaking however not as bad.

Upon reading, some of the cranks have a serrated edge that needs to be taken into consideration and some use a sealant in addition to the kit. Some swear by the old soap on a rope as well.

Good luck with old leaky. I'm just used to it as I have had pontipigs for 30 years now lol and sick of trying to fix it lol

[Sirrotica]

From someone that has done rear main seal replacements, many, many times your mechanic is mistaken if he thinks he can drop the pan on a Pontiac Stratosteak engine, in chassis, (a feat only for the very determined), pull the rope seal out, and replace it with a 2 piece lip seal, and then not have it leak.

The probability of success would likely be 10%.

If it has a factory crank in it the serrations will soon abrade the new seal. The crank should be pulled to smooth the serrations so they won't abrade the new seal. If you should somehow get the new seal to not leak upon fire up, it will leak soon after, simply because the serrations will cut the lip off of the seal.

Save yourself time and money in the long run, and remove the engine, put it upside down on a stand so you can work on it comfortably. You'll have a much better chance of success if the engine is out of the car.

If you don't want to pull the crank out, and smooth out the serrations for either the 2 piece seal, or the 1 piece seal, you would need to try the graphite impregnated rope seal. Best Gaskets makes them, as well as do other companies.

If your guy tries to do it in chassis, I can tell you he'll probably never do a second one, and the success rate is very low, compared to pulling the engine, and doing the repair on a stand.

My advice is to always pull the engine and in the long run save you time, money, and a great deal of frustration. That advice goes for any rear main seal you choose to use in your engine,

I can't truthfully comment on the 1 piece or 2 piece, as I've never used anything but rope seals, someone else will probably comment on their luck that has actually used them.

[kingbuzzo]

Exactly...I told him to replace the seal before he put the engine in the car...he didn't...then try to save his own time to replace it in the car

His lesson not learned and I'm living with it...

He wasn't too happy about the headers at least...lol

[Baba O'Riley]

Thanks to you both. Sirrotica -- okay, if I still go half-ass on this so the crank is dropped, or pulled altogether, what is the best tool for smoothing out those serrations?

[tom s]

With your situation I would use the Best Gasket Company Grafite rope seal.Do it right and pull the engine.JMHO,Tom

[Sirrotica]

Originally Posted by Baba O'Riley

Thanks to you both. Sirrotica -- okay, if I still go half-ass on this so the crank is dropped, or pulled altogether, what is the best tool for smoothing out those serrations?

Just a flat file to take the high spots off, I would then use a stone to finish it, it can be done by hand, or you could put it in a lathe. The main thing is smoothing the high spots off so they don't tear off the seal lip. The serrations are like saw teeth on a composite seal.

As Tom has suggested, the Best Graphite rope style is what the Pontiac engineers designed the block for originally. When they machined the groove it sometimes isn't square, or perpendicular to the crank. The composite seals need to be square in that groove to work properly, and if the factory did a half assed job, you usually have problems getting them to seal well. Usually when that happens, the mechanic ends up going back to a rope seal anyway. The serrations work fine with the Best seals, no modification needed.

It can be a real sore spot for your mechanic when it's all back together, and it leaks, because most of the money you spend is for labor, the seal price is insignificant. This is the reason no shops want to warranty a rear main seal, doing it free the second time, or the third time is costly for the shop. It's a tough job the first time, doing it 2 or 3 times after you were paid for it the first time could tie a mechanic up 1-2 full days each time it's done. A shop owner can't afford to pay someone to spend all that time, if it leaks after the first time. Anyone that is telling you no warranty, has already likely had to eat the labor at one time, or another.

If you work flat rate in a dealership, you do a rear main and it leaks, you get to do it for free the second time, doing one freebie in a week, will knock you down to 3 days pay, that you worked for 5 days. Been there done that, never would do it again, nor suggest any mechanic take a flat rate position.

Here's a link to Tin Indians website with information about their seals and the serrated crankshaft:

https://www.tinindianperformance.com...ear-main-seal/

[Formulabruce]

Only thing worse than changing these Rear main seals in the car, is doing it on Flat rate under warranty, and That I Did do...with asbestos rope seals too. Factory leaks were Not common, but rope pinched in the cap could cause it.
We had a "shoe horn" type tool with a "J" number on it I used to get the block side slid out.
Modern Rope seals have a pretty good rep, just cut them even and clean and use a dab of RTV at the ends.
Rear mains with rope rarely leak at the 'seam" .
Good luck!

[Baba O'Riley]

Okay good. Definitely one of those "manage your expectations" things if I do it that way. Appreciate each of you taking the time.

[kingbuzzo]

Are you going to pull it out or roll the dice?

[Baba O'Riley]

Still deciding, because I'm not the mechanic most of you are (nowhere near) so I'd have to find a shop I trust to do the pull and put it back without a bunch of new things flaring up like electrical bugs. My longtime mechanic retired recently.

[kingbuzzo]

Yes, it's hard to find someone that has seen a carb before these days...lol

Hopefully you can do some other maintenance to make it worth your while.

My old T/A leaked for twenty years and I just learned to live with it - built in oil change...lol

[Norwood]

Don’t take any shortcuts, do it right the first time.

[kingbuzzo]

Maybe if/when I hit the lotto and buy a butler block...lol

[76TA462]

Been through the RMS hassles too many times. Originally after the first build (1983 - first time I owned a Pontiac so I spun main bearings before I knew about the lower rpm 455 LOL) still using the rope, but it worked great for years until it didn't so that was okay by me. More recently (2010) I (the shop) used the BOP Viton RMS02 and it leaked. They did that pull the pan short cut and not only was it frustrating to deal with this idea, it didn't work very well. Had a shop experienced with this do it again (2012) to fix the leak, and also on the next build in 2020 and again both used the BOP Viton RMS02 and all four rotation holes were filled with silicone). No problems since the last two times, and after so many years of a runny nose RMS it sure feels good.

[Baba O'Riley]

If I go all-out, with the engine pull... if I opt for a one-piece seal, should I replace the original crank? What's everyone's take on the necessity of this?

[tom s]

If you want to use the lip seal just have the serrations polished.FWIW,im 100% with the 1 pc BOP seal and 100% with the Best Gasket seal and 50/50 with the BOP 2 pc seal.Tom

[Formulabruce]

Originally Posted by tom s

If you want to use the lip seal just have the serrations polished.FWIW,im 100% with the 1 pc BOP seal and 100% with the Best Gasket seal and 50/50 with the BOP 2 pc seal.Tom

/\/\/\ I agree 100% . I will add, follow the directions with the 1 pc seal.

[Formulabruce]

Originally Posted by tom s

If you want to use the lip seal just have the serrations polished.FWIW,im 100% with the 1 pc BOP seal and 100% with the Best Gasket seal and 50/50 with the BOP 2 pc seal.Tom

/\/\/\ I agree 100% . I will add, follow the directions with the 1 pc seal.
Also, while upside down, after you button it up, SMOKE it to be sure you nailed it.
Smokers are cheap leak insurance and are used for leak checking and vacuum leaks too.

[tom s]

We started using a chain fall with the crank suspended at both ends to do the one pc seal.Makes life much more EZ.Tom