rear main seal m38a1

RHarris · Post by **RHarris** » Tue Aug 09, 2011 5:51 pm

Anyone with ideas on the best rear main seal? Rope or rubber what is the best / easiest? Thanks for any input, all I can find around here is the rope type. RHarris

Post by **wesk** » Tue Aug 09, 2011 11:40 pm

If your crank is dimensioned for the rope seal you have to use the rope seal. Do a search for rear main seal both here and on the G503. There's thousands of words in several threads about this topic already written. The formed lip type seal is of course the easiest to install but it has a very narrow tolerance of crank dimensions at the lip's sealing sealing surface. Also many machine shops fail to polish this lip sealing surface when they turn cranks.

RHarris · Post by **RHarris** » Wed Aug 10, 2011 4:29 am

Thanks for the reply. I went through a lot of the posts and will probably have to take it apart and check it out. Robert

Post by **wesk** » Wed Aug 10, 2011 11:06 am

A lot of chest thumping folks will tell you just do it laying under the jeep.

Well for the couple of hours taken to remove the engine and mount it on a stand and rotate it upside down and do a proper job of it makes the 2 or 3 hours worthwhile. Also gives you a chance to get a good look at the overall engine while it's out.

artificer · Post by **artificer** » Wed Aug 10, 2011 1:40 pm

Agree with Wes engine should be out & if you have the right seal I would use the narrow style neoprene which fits in the grove like the rope style....the problem ones are the ones which are wide & straddle grooves.
The journal the seal runs on needs to be perfect if a good seal is expected.

madmike · Post by **madmike** » Thu Aug 11, 2011 12:31 pm

I just went thru this too and did a lot of research. The engine builder/machine shop I use mentioned the later neoprene seals are better to use and last longer. But...I spoke to John at Midwest Military and he related that his builder has had problems with SOME of the neoprene seals produced now. His gaskets kits have the rope seal, and if installed correctly, will provide years of trouble free service.

I also heard that if you are installing the seal to stop a leak, and not as part of a rebuild, it is much more difficult to get the neoprene seal in without damage. You really need to drop the crank slightly (probably for both types) and put some silicone on it to slide into place. The rope seal must be cut long enough to ensure a complete seal between the halves and I suppose this may be the hardest part of an engine-in -the-Jeep installation.

I suppose it would be better if I posted this reply after I started my engine and looked underneath but I am not quite there yet. I recall using and installing rope seals many years ago and not having a problem with them. The neoprene is easier to work with if it does the job. Good luck no matter what you choose.

Post by **wesk** » Fri Aug 12, 2011 8:22 am

The main issue with seal selection is the condition of the sealing surface on the crank. Most important is it's dimension. Many original rope seal cranks do not have the correct dimension required for the lip type preformed seals. There is a published service letter with the dimension issue listed on it. Any pitting, scratches or excessive wear by lip of seal in journal will result in a leaking installation.

An under the jeep installation is without any guarantees.

It also pays to remove the engine and make sure your probable rear main seal leak is not really a rear cam journal expansion plug leak.