VCCA Home Forums GENERAL DISCUSSION General Discussions neoprene rear main seal for 235 engines

has anyone come up with a neoprene replacement for the blue flame 6's? our daughters 54 corvette, with over 40K miles since I restored it in 1980s, is puking excessive amounts of oil. if available, can you all direct me to source? thanks guys, mike mccagh

The neoprene seal is for 1955 and up blocks only. The seal grove is too deep for it to "work" in previous years. If it is pouing out oil the wick seal is probably rusted on to the crankshaft and spiniing in the seal grove. This can happen on cars that sit unused for periods of time.

thanks gene. mike

Mike

Talk to Gene about the "improvised" neoprene seal he used on his '50 engine. I used his method on my 216 in 2015 and it has not leaked since. Thanks, Gene. Scares me sometimes to not find oil under the car.

Replacing the rear main can sometimes turn into a project involving more than just the seal. Don't ask me how I know that.

If the seal is used on a pre 1955 engine the seal wil drop too far into the grove and the lip will not contact the crannkshaft. My idea was to bring the seal out farther. What I did was use a piece of a nylon wire tie under the seal. Now this made the seal too long so I cut some off of the ends of the main bearing cap seal. I did put a light coat of RTV sealant behind the seal.
It is important the clean up the area thaat the seal rides on as it could have rust on it.
I did mine several years ago, drove it to Colorado etc. and stll not leaking. The engine has never been apart at 55,000 miles and used about a quart of oil in 2000 miles which was what they did when new and considered great at that time.

Agree with Tiny. The leak is often caused by the crankshaft dropping away from the top part of the seal. Packing the top piece tighter around the crankshaft then lifting it back to its upper limit, then put a extra packing in the lower seal groove.
Tony

That is the advantage of the neoprene seal. The seal lip has some give t it where as the rope seal does not.

Over the years I have replaced the rear seal (rope) twice (both upper and lower) with negative results. They leaked just as bad they did before I replaced the seals. Suspect it was because I stretched the upper seal while pulling it in. I have tried Tony's method once with the same negative results. Gene's improvised neoprene seal installation is the only method I've found that works unless you pull the engine and install the rope seal as the book sez. And with today's seals I understand that is questionable as they seem to deteriorate quickly. I have about 6.000 miles on my neoprene seal now and have yet to see the 1st drop from the rear main. Even my rope seals back in the day used to seep slightly when new. Gene, I did not use any "stickum" but offset the 2 seal halves about 1/2 inch so that they were not at the rear main cap split.

Mike, were you at the Central Meet in Indiana last summer - with your 1940?

gene: i wasn't at the central meet. i usually just make the 5 year meets. i've not owned a 40. i just sold the 29 convert. landau, still have the 39 woodie and a 30 roadster pickup in addition to corvettes and street rods. regards, mike

Sorry - I meant Mike Deeter.

Yes. Did not have the car judged this time. Also did not spend much time there as my family lives straight East on Hwy 26 in Fairmount, IN. Did help tab tho and made the awards dinner..

I saw this and it gives fuel for thought in the case of a complete rebuild.

I was there also and did not know the 1940 there was yours. First saw your name listed in the booklet AFTER I got home.

Greg H that was a pretty interesting video on modifying the rear main to accept a a neoprene seal. Thanks!

The key to success on rope seals is packing them. You have to really focus on packing them in there tightly. I made a "packer" using an old drum stick. I have a set of plastic seal press tools which I used in combination with the drum stick to mash the rope seal in as tightly as I could. I also am using BEST brand seals which have graphite impregnated in the square rope which shape also helps.

GMC engines are a bit different and modifying for neoprene seal would be hard to do, but here's the photos of the GM rope seal tool and drumstick I used to finally get in front of the "continuous undercoating system" that was my rear main leak. You have to really pack the seal in as tightly as possible before trimming the ends. Some of our GMC engine owners have had better luck with the old asbestos seals but they are now all but impossible to find. Packing the rope is key.

The few of these that I have done I mounted the cap in a vice and used a hammer handle in a sliding motion on the around the area the crank would run. Admittedly I havent done any of the top seals with the crank in place.
Tony

Someone I know had their top seal expanded by fishing a nylon tie between the seal and block after loosening the main bearing caps. I don't have all the detailed steps but it solved the leak problem for a well know Canadian member.

The problem with that approach on rope seals is that they will spin in the seal pocket. To solve the spin problem with the BEST square rope gaskets, I drilled a small hole in the bearing cap and then cut the end off a nail and tapped it into the bearing cap hole to pin the rope seal so it couldn't spin and that worked great. Been holding well for 13 years since.

As a dealer for Best Gasket Inc and their supposed rear main seal troubleshooting person, I though I better throw in my 2 cents worth of information.

Replacement of the engine rear main seal in chassis of any engine can be an ultimate bear. Even professionals with years of experience have a hard time doing this much less the weekend mechanic. The reasons for using a rope rear main seal is that the rope is molded and "rolled" into the seal groove which will fill in any irregularities such as with a cast rough finish groove and centers itself with the crankshaft seal journal once installed. The original ones were made to seep somewhat as this is what lubricated the asbestos rope seals. The rope seals sold by Best Gasket are made of Teflon braided rope impregnated with graphite and are industrial quality ropes. Any rope seal has to be installed correctly. If the rope seal is not 'rolled" in all the way to the proper dimension and has high spots will cause to much drag on the seal journal resulting in burning the seal causing a leak if not too tight or the crankshaft seal journal can move the rope causing is to spin in the groove and turn it into a bunch of pieces or shreds. This can easily happen when the groove has a nice smooth machined surface and the rope seal has nothing to anchor to. To keep this from happening, most or all the rear main seals that Best sells come with a 1/16 inch roll pin in them that goes in a hole you drill in the center of the groove in the rear main bearing cap. Attached is some information that we send out with all rear main seals.

Always remember that bearing wear or clearance will make a huge difference on how a rope seal will work.

The main reasons that a replacement rubber rear main seal with not work in place of a rope rear main seal are the depth of the seal groove, the width of the seal groove, the centering of the seal groove to the center line of the crankshaft and the condition of the seal journal face itself. The rubber rear main seals works with about a 10 thousands of an inch plus or minus tolerance. This is why they do not work on most of the earlier engines. The rubber rear main seal was made for 1956-62 235 & 261 engine that did not use main shims. If the groove is to deep, then the seal sides will not butt together to make a seal plus the seal lip will not contact the crankshaft correctly. If the seal journal is slightly off center from the center line of the crank, then the seal will be totally collapsed on one side and hardly if even touching on the other side causing the tight side to burn and melt from excessive pressure on the journal. If the seal journal has been ground because of a rough or corroded surface finish, then this can make the OD of seal journal to small for a rubber seal. This it why on the older engines, you can shim up a rubber seal as long as it contacts the crank seal journal correctly but this take some finesse.

I have heard may different tricks for putting rope rear main seals in chassis in the engine block. Using a piece of piano knotted on one end pushed through the rope seal, tying a piece of fishing line on one end, the use of a sneaky pete tool or a Chinese finger tool. The old guys in a pinch would just pack the engine block rope in tighter and then add some more rope to groove to fill it up.

For more information on rope and rubber rear main seal information, click on these Best Gasket website links https://bestgasket.com/about-our-products/ and https://bestgasket.com/fanfare/

Hope this helps all of you out.

The way Oldsmobile suggested to replace the rear main rope seal in their last V-8 engines was to use a blunt tool (and small hammer) to compress the upper rope seal and cut of a short piece of the lower seal and stuff it into the gap Then replace the lower seal.

Problem is sometimes the upper seal has turned to stone or seals are spiing with the crankshaft.

Thanks for taking the time to address this. Interesting reading and learning.

I talked to Armin Brown (owner of Best) many times as we worked together in '06 to improve the seal in both size and prevent it from spinning. I put this pin in my lower rear main cap which did end the spinning problem with the rope seal. My rear main seal is not completely sealed, but it's 95% and only an occasional drip and if BEST is now including a pin in the kit, then I would expect that came from our collaboration 14+ years ago. Pin definitely works and is highly recommended if you are using this type of rear seal.

Thanks for your post.

I am not currently working on a seal but I'm just curious. and as info, just how much of the pin has to stick up into the seal to keep it from turning. Its hard to tell from the picture... In case I need to do one in the near future...........or i could just order it from Best and there is probably some instructions in there. (yes, i know you don't want it to damage crank)

You can more or less tell from the photo that the pointy end of the nail and a slight amount of shank was all I was I after. I didn't want the end of the keeper to poke through the gasket and end up scoring the crank, but you can mess around with lengths and drilling depths to get it right. The addition of a pin from BEST is news to me but is interesting. If I were doing it again, I would use a cylinder and not a pointy ended stopper. The cylinder would probably hold and resist it from slipping the pocket better than the nail. I was unaware that they added that to the kit. Again for me, the key is compressing the living daylights out of the rope by pushing the ends in while using the rope seal tool to get as much density into the rope as possible. Just mashing it down with a socket or roller will elongate the rope and is counter productive to trying to make it fat in the pocket.