Rear Main Seal

[James_Douglas]

In a few weeks when I swap the trans out...

I want to replace the rear main seal as it is leaking way too much. I expect some leaking, but the seal on the new engine is leaking a lot more than the old tired one did.

I suspect that something is wrong with the seal or the person at the machine shop that put it in.

The engine block is from a 1953 Desoto (251 cu.in.). I think there are three seal types over the years.

1. two part seal.

2. one part seal.

3. neoprene seal.

The first one requires the fluid coupling (or flywheel) to come out to change. The second one does not. Both 1 & 2 require the all the mains to be loosened 3 turns.

I just read in a MOTORS Manual that Plymouth used a neoprene seal in 1953 and onward that did not require dropping all the mains three turns, just the rear main with the seal.

Does anyone know if any of these seals are inter-changeable and specifically, can the neoprene seal be used in a 251 block ?

Thanks for any help on this one.

Best, James

[blueskies]

James-

I don't have a direct answer to your question... but I used the neoprene seal on my '50 218/230 block.

My engine had the original seal still in place when I pulled it. It was a two piece face mount seal with a "rope" type material for the seal.

When I ordered a new seal, I wasn't sure if the neoprene type would work, so I bought two types. One of the two was a face mount similar to the original, but it had neoprene or some kind of rubber for the seal material. The other was the neoprene seal that fits into the groove in the block and rear main bearing cap. Both of the new seals are two pieces, top half and bottom half.

I had heard that the early blocks didn't have the groove for the neoprene seal. It turned out that my block did have the groove, and the seal fit perfectly.

This seal is installed by removing the oil pan, and the rear main bearing cap. The top half of the seal will slip into the groove around the crank. I don't think you would have to remove the flywheel to install this seal, but you probably will need to remove the flywheel to remove the old face mount seal.

One curious issue that I found with my rear main bearing cap... It had a hold about 3/8" diameter through the face of the cap. This hole was previoiusly covered up and sealed by the original face mount rear main seal. With the new neoprene seal, the hole was open from the outside face of the cap into the oil pan side of the cap, with no seal at all. I filled the hole with JB Weld so eliminate the problem. I don't know what the hole was for, but I've heard it had something do to with fluid drive or Hydrive transmisions. Does your rear main cap have this hole?

Here's some pictures. Hit reload on your browser if they don't show...

In this shot you can see the groove machined in the block for the seal just outboard of the thrust flange on the crank.

Here's the rear main bearing cap with the seal in place and the mystery hole. The three threaded holes are where the original two piece face mount seal bolted on.

The inside face of the cap-

And the cap with the hole filled-

Pete

[James_Douglas]

Pete,

Did the seal you put in have a steel backing (scrapper) on one side ?

James

[blueskies]

Pete,

Did the seal you put in have a steel backing (scrapper) on one side ?

James

James- The seal I used was rubber on both sides, but it might have had a steel core... can't remember now.

I bought it from Vintage Power Wagons.

Pete

[Don Coatney]

This is what my rear seal looks like. I did not have the mystery hole in my

bearing cap that Pete had. I believe the seal had a metal ring but it was

several years ago when I installed it. My rear main seal weeps but does not

drip. I went about 6,000 miles between oil changes and never had to add

oil. I used super glue to affix the rubber pieces as pictured.

[grey beard]

You're getting good advice here. The early blocks all used the rope seal, which worked much better on these engines than they did for Ford's motors. Their 272/292 family Y blocks leaked from almost brand splinter new. The second generation seal had a metal plate made as part of it and used three screws in the three holes Pete showed in his one photo. To replace the top half of that type seal you would of course have to remove the flywheel to get to the three screws. It is my belief that the later style slide-in neoprene seal also shown in Pere';s photo is a later design made to work in all but the earliest blocks - any of them that had room for the seal to go in the groove in place of the original rope or in place of the earlier style neoprene. If you can find someone who carries the neoprene seal without the metal brackets, that would be the best of both worlds for a leak repair - offering the better seal design without the need to pop the flywheel. JMHO

My engine was the early block design, so I used the rope seal - hope it never leaks.

Good Luck

[James_Douglas]

Thanks Guys,

I found a photo of the rear main and I think it is the type that used the two part rubber with the metal reinforcment. I think I can change this without taking the fluid drive out.

Thanks, james

[greg g]

does anyone have a non leakig rear seal?? On my 218, the crank was corroded in the seal area. It was sent out for spray welding and machining and a newer style seal put in. Started seeping about a month later, the whe the 230 was rebuilt, it got the new style deal as it is a 56 block. That one is seeping a bit also. In my 1/2 quart avery 500 miles usage, I'm betting 90% of it leaves via the rear main.

So all you guys who have no leaks step up and be counted.

[40phil41]

does anyone have a non leakig rear seal?? On my 218, the crank was corroded in the seal area. It was sent out for spray welding and machining and a newer style seal put in. Started seeping about a month later, the whe the 230 was rebuilt, it got the new style deal as it is a 56 block. That one is seeping a bit also. In my 1/2 quart avery 500 miles usage, I'm betting 90% of it leaves via the rear main.

So all you guys who have no leaks step up and be counted.

Mine leaked from the day I installed it.

Phil

[blueskies]

So all you guys who have no leaks step up and be counted.

My rear main doesn't leak, but my tapet covers are leaking quite a lot... One of my spring projects. They aren't easy to seal because of my Langdon tube headers... The heater box, intake, and exhaust has to be removed in order to get the tappet covers off... Which is why they have been leaking for the last 8 years...

Pete

[old woolie]

I replaced the two part seal with the metal plate and three bolts in each half on my 218 without removing the flywheel and while it was still in the car. Had to heat and bend a thin box end wrench two or three times to get the right combination,7/16, I think. Used a thin telescopic magnet and a long thinflat blade screwdriver to start the top center bolt. Lots of patience required. And yes it does leak slightly but nothing like before.

[Don Coatney]

Pete;

My valve covers initially leaked as I used rubber gaskets.

I switched to cork and fixed it. I found the leaks while I

was running my engine on the test stand before I installed

the engine in my car.

[blueskies]

...

I switched to cork and fixed it....

Don-

I have the cork gaskets, but I didn't use any kind of sealer on them as I knew I'd be doing a valve adjustment after break-in... . Haven't done that yet either, and it needs it. On my to-do list.

Pete

[grey beard]

Mr. Old Wollie's story almost reminds me of the gynacologist who did a ring job on his engine working through the exhaust pipe . . . (just kiddin . . . )

[James_Douglas]

Pete,

I got a set of those finned valve covers and just put cork gaskets across the entire thing using sheet cork. Then you don't have to worry about getting the gaskets on correct...just bolt the cover down.

I sent back the Langdon tube headers for Q & A reasons one of which us that they are so close to the valve covers that they would have to come off to remove the covers.

James

[blueskies]

Pete,

I got a set of those finned valve covers and just put cork gaskets across the entire thing using sheet cork. Then you don't have to worry about getting the gaskets on correct...just bolt the cover down.

I sent back the Langdon tube headers for Q & A reasons one of which us that they are so close to the valve covers that they would have to come off to remove the covers.

James

Thats a good idea James. With the stock tapped covers, the gasket fits around the stamped cover, and stay put for the most part.

I knew that the Langdon headers were a tight fit to the block when I put them on. I didn't think it would be too big of a deal to take them off when I needed to, but now that they are on, and the heater and heater duct are in place, I'm not too excited about taking the whole thing apart... Can't really even see the headers without looking for them...

Someday I'd like to replace the headers with Fenton type cast iron headers, and redo my exhaust. But for now, it will have to do.

Pete