Rear Main Seal Question

[oilleaker1]

I'm in the middle of overhaul and I'm confused as to which type rear main seal my '51 MC L head motor should use. Rope?, 5/16 inch wide seal neoprene?, wider seal neoprene?. Do you measure the crank machined surface for width to figure out the type? The engine was previously all messed up by a mechanic that knew nothing about it. I don't want to go by what was in it, cause it's probably wrong. He did alot of things wrong. Too much to go into detail. The motor is definately a early '51 military motor. The well of knowledgw here is what I appreciate, that is why I ask. When I say width: I mean front to back of the crank, not diameter of the crank. My CJ3A or civilian shop manual just shows a seal in the parts break down and that's not enough info. HELP!!!! John

[oilleaker1]

TM 1804 A says rope. It doesn't talk about rolling in the rope with a dowel, or leaving one end short and the other long with a similar arrangement on the other side bridging the gap. It simply says to push it in and cut it off flat with the surface. My motor had the narrow neoprene lip seal. What's the vote out there?

[Oldsalt]

I think I'm confused on this. I had thought that all the MC engines used rubber seals because of sealing for the fording system. The TM 1804A that I just downloaded speaks of Rubber packings in paragraph 143. Where did you read about rope?

The advice I've read here many times is to put back the same as you took out. Since you took rubber out, I'd put rubber back in.

[wesk]

The TM 1804A that I just downloaded speaks of Rubber packings in paragraph 143. Where did you read about rope?

John just confused the two vertical round rope like seals for the two sides of the rear main cap with the early rope seals used around the crank journal. TM 9-1804A only covers the late lip type seal which uses the same two main cap side seals that the earlier rope type seal engines used.

Here's the long and the short of it all.

WWII and early post war CJ's used a rope seal.

The MC and MD blocks used the lip type two piece seal.

In the 1990's the Victor Lip type seals were improperly sized and had a high failure rate. Avoid buying old NOS surplus seals. Seals in current issue victor and Felpro kits are fine.

A pitted or otherwise damaged sealing area on any of the cranks will result in either type seal leaking. Machine shops often overlook cleaning up and polishing this seal area

The same crank fits all the gear drive cam 134's. But the early manufactured cranks used in the rope type seal blocks did not have the dimension of the sealing area kept to a close enough tolerance to work with a lip type seal if that crank showed up in a later lip type seal block. Since you have no way of knowing where your crank originated from, you must check this dimension to be sure the crank you have can be used with a lip type seal. This strict crank sealing surface diameter tolerance is 2.302-2.312". Smaller and the lip seal will not have enough tension on the surface. Larger and the lip seal will be too tight and will fail from heat build up.

The bulletin below makes this quite clear:






This sealing surface is pitted and unusable.



Here's a properly finished sealing surface.




Here's the crank & seal dimensions we are talking about.



Here's the cap dimensions.

[RHarris]

I could not find anything but the rope type seal from Fel-pro around here. I used this in a 53 model and no leaks yet. Robert

[artificer]

I would be careful using any neoprene seal which straddles the groove & hangs in toward the flywheel....these have been troublesome & cost folk heaps of $$$.
There are narrower LIP neoprene seals which fit only in the seal groove & these are good.
The rope type seals are fine but will not last so long & they MUST be rolled into place then trimmed carefully to dimension WITH a little crush.

IF IT FEELS TOO TIGHT TO TURN THE CRANK, IT IS TOO TIGHT.

[oilleaker1]

I saved my narrow lip neoprene seal and I'm copying this to take to the machine shop. The Felpro kit only had the rope seal in it, so the shop owner ordered a neoprene seal------20.00 each. I think my seal surface needs to be polished cause it looked worn and grooved. Thanks for saving me again! Wes, excellent !!! You get 20 points credit at the next show now, so your lug nuts will pass! This really helps, if any of you guys are doing yours, copy this and take it to your machineist!!!! John

[wesk]

I agree with John that the narrow seal is the better choice. Just make sure it is not a NOS 90's vintage Victor.

[oilleaker1]

Well, the crank seal area is polished nice, but the lip seal was the fat one with the extended lip. Does anyone know who has the narrow ones??????It may be rope time for me. John

[artificer]

Pic courtesy of J Barton's tutorial G503



There are 3 seals shown above....my experience & that of many others is the top one [also shown below]
1st which is a Victor which is a full "WIPER" seal is no good....in my case three seals were damaged when received new, with the flashing bad.



Also if fitted up the Victor will generally be too tight on the crank causing eventual seizure of the rear main bearing. There are numerous example in the Jeep community.

Wipers contact a large area of the crank & when too tight cause copious amounts of frictional heat.


2nd is a thin narrow neoprene 'LIP" seal & I would recommend, if obtainable. It has very little contact or drag on the crank & the crank must be clean.

3rd is the rope type woven "WIPER" seal & there are 2 types only the thin narrow style [as shown in Barton's pic] which fits & slides into the groove is acceptable.

@ the end of the day it is all about feel & knowledge....the shaft when all fitted up must feel & turn very smoothly with acceptable drag. Like I said earlier if it feels too tight it is too tight

[wesk]

The war story on the Victor seal debacle and the crank problems associated with it came from the bad batch of Victor seals put out throughout the 1990's. Victor refused to acknowledge there was ever any problem with their seals. Most vendors were smart enough to stop selling them but even today they show up as bargain NOS. Its buyer beware when you buy anything not current.

Of course any seal from any maker that arrives at your door damaged should not be used. I am not aware of any current production seals that have any on going problems when properly installed.

Do take the time to read through these two threads before making your decision.

http://www.g503.com/forums/viewtopic.ph ... 15e93eb721

http://www.thecj2apage.com/forums/engin ... page1.html