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Rear main seal - which one?

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JeepSaffer View Drop Down
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    Posted: 11 Jan. 2019 at 3:39am
I have three different rear main seals available to use from my parts stash, and want to know if there is a clear winner that I should be using on my new engine build.



On the left is a seal that came in Walcks "engine gaskets and seals kit". Looks like neoprene rubber.

In the middle is a seal that is apparently NOS, that came from QTM a few years back. It appears to have some kind of fabric or material on the seal area, which would actually form the wearing part of the seal.

On the right is a rope type, which came from Peter deBella. 

Here is a close up of the NOS seal. Some part numbers and some installation arrows are visible.



That's what I have available. Is there a clear winner as to which one I should be using? My seal area on the crank is not brand new, but not terrible either.

Thanks,

Mike

 

1948 CJ2A #204853 in South Africa
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swmoboy View Drop Down
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Post Options Post Options   Thanks (0) Thanks(0)   Quote swmoboy Quote  Post ReplyReply Direct Link To This Post Posted: 11 Jan. 2019 at 8:18am
Following cause I'm fairly certain I need a new rear main seal.  Every other time or third time I park the ole girl she leaves me a puddle on the floor and sometimes it's a significant amount.  
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Post Options Post Options   Thanks (0) Thanks(0)   Quote JeepSaffer Quote  Post ReplyReply Direct Link To This Post Posted: 11 Jan. 2019 at 9:23am
I found this thread from some back, but it has some pretty useful information in it:

In summary, Sean (who else? LOL) indicates how to tell an original Victor Gasket seal from a cheap imitation:

  • Old-style Victor seals are marked  : "VG  49650  800093 Install -->"
  • New-style Victor seals are marked: "xx  VG  49650  800093 Install -->"
I don't have the numbers before the VG, so it seems I do have an original older style. I guess that is  good news. 

I also found this, which makes a lot of sense:




In summary:
  1. Some of the early L134 blocks provided more space for a seal than the later blocks, and were designed for a rope seal. Meaning that forcing a Victor type seal designed for a later block into an early block designed for a rope seal, can mean that there is not enough clearance for the crank to turn in the seal. This can lead to failure of the seal.
  2. Measure the seal area dia of your crank. If it is within the limits shown, you can use the later type seal. If it is larger than the limits shown, you need to go with a rope type seal.

I will wait for anybody else to chime in, but I think my way forward is exactly as above: measure my crank seal area dia and if it is within the limits above I will go ahead and use my NOS Victor seal. If my crank is larger I will use my rope type seal. My block is serial number 153955, so is not "early" for L-head, but certainly early for F Head.
I have also picked up that when installing your seal you should not feel more than a slight drag due to the seal on the crank, when the caps bolts are torqued down. If there is anything more than this, you are trying to force too tight a seal into too small a gap and you will likely have problems with failure in the not too distant future.

So I will go with the NOS Victor seal if my measurements on crank dia check out, unless someone thinks this is a terrible idea! Key being also to rotate the crank by hand after installation and see how much drag there is.

Any other good ideas?


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Post Options Post Options   Thanks (0) Thanks(0)   Quote Spinnas Quote  Post ReplyReply Direct Link To This Post Posted: 11 Jan. 2019 at 11:02am
Personally I like the rope seal, it's more forgiving.
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Post Options Post Options   Thanks (0) Thanks(0)   Quote Mark W. Quote  Post ReplyReply Direct Link To This Post Posted: 11 Jan. 2019 at 11:57am
A key to getting this to seal up is the condition of the seal surface along with as the above bulletin states the diameter of the narrow sealing surface. My crank was a little messed up in this area and after the original machine shop determined the mains and rods were within spec to not grind the crank. I noticed they also did not mess with the seal surface. I ended up taking my crank to a true old school (been around since before WWII) crank grinder. There I was told that yes my crank was usable as is but it was on the last 20-25% of its life at that dimension. SO I had the crank ground to .010" under and then he cleaned up the seal surface to the min 2.302 to get as much of the rough surface out as possible. I am running a Fel-Pro Rope seal. Sometime this summer I will find out if its working.
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1948 2A Body Customized
1949 3A W/S
1957 CJ5 Frame Modified
Late 50's 134L 9.25"clutch T90A D18 (1.25") D44/30 flanged E-Locker D25 5.38 Since 1962
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Post Options Post Options   Thanks (0) Thanks(0)   Quote athawk11 Quote  Post ReplyReply Direct Link To This Post Posted: 11 Jan. 2019 at 3:35pm
JeepSaffer,
I think you have a perfectly reasonable plan of action.  Based mostly on what I've read on the forums, and in Bob Westerman's book, my personal dividing line is...

If the engine was built in the period prior to the development of the M38, I will stick with the rope seal.
If after the M38, I will use the NOS neoprene seal... if the seal surface measures out good and the surface is not all beat up.  Of course this assumes the crank is original to the engine, and hasn't been 'improved'.

I am not lucky enough to have a later engine or an improved crank surface.  I use the rope seals.  And unfortunately, mine all leak a little.  Particularly after pushing the engines to their limits.


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Post Options Post Options   Thanks (0) Thanks(0)   Quote JeepSaffer Quote  Post ReplyReply Direct Link To This Post Posted: 12 Jan. 2019 at 8:51am
Thanks Tim, you raise interesting points...

My block is from a CJ-2A engine, so was definitely built prior to development of the M38. According to your mantra that would mean "use the rope seal".

However the crank came loose in a pile of parts and was not installed in the engine (I bought a bare block), so it is possible the crank is later than M38. There is no way of knowing.

My seal surface is pretty good, but could do with a little polishing. The surface looks more "stained" than scored or grooved or chipped.

I did mic out the seal surface. The AERA Tech Bulletin says 2.302-2.312 = OK for neoprene seal. Mike mics out at 2.307. Can't get more perfect than that. 

My current understanding is that you have two options, each with their own advantages and possible downfalls:
  1. Use a rope seal. More forgiving, less chance of heating up and failing. But less chance of a "tight" seal and hence expect a few drops of leakage from your rear main.
  2. Use a conventional seal. Less forgiving, only fit in certain engines/cranks, seemingly some bad reproductions out there. Too tight will lead to heat and early seal failure. BUT, if you get it right, you get an improved seal over a rope seal and hence better chance of less leakage.

Based on the only definitive measure out there that I have found, which is the AERO Bulletin, and the fact that I seem to have a genuine NOS seal, I plan to test fit it and check the drag on the crank. If the drag is minimal I will go for it. If the drag is concerning, I will swap out for the rope seal.

I've got a few more days before I actually try this out, so chime in if you think any differently. 
1948 CJ2A #204853 in South Africa
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