I noticed over the summer month my truck had started marking its spot where I have been parking it. Nothing really drastic at first but it kept getting progressively worse. Today I noticed a drip trail out of the garage and a small puddle where it was parked. Looked underneath and noticed the front of the pan and the differential cover was dripping after I returned home from a ten mile trip. Cleaned everything off and found that the front seal is the culprit. Then I took a large screwdriver and visually checked the crankshaft end play. Well the book says it should be around .012" max which without using a dial indicator would be slightly noticable. That is not what I found. With my uncalibrated eye I would have a guestimate of somewhere in the neighborhood of .030" - .040". Plan is to get a true reading tomorrow. While checking the endplay I can hear the crankshaft shift position on the main bearing thrust surface. I remember reading about a mainbearing problem in the 4BT engines that was causing excessive endplay. Could there be a similar problem in the 6BT's? Also, for those who have replaced a leaky front seal, did you check your crankshaft endplay and was it within the specified tolerance? Can the engine wear out the thrust bearing surface on the main bearing without destroying the crankshaft? This engine has 122K miles.

 

Yes.

While I have no experience with it, from what I've read here in these forums, the manual trans clutch thrust is the culprit.

Others with 1st hand knowledge will chime in shortly.

 

Sure, you can wear out a thrust bearing without damaging anything else. I just put a new thrust bearing in an M11 and didn't find anything else out of spec.

The 6BTA I'm using for my conversion (pics in a thread posted below) I measured 7 thousandths. 7 Tho is enough to hear a slight clunk and you will be able to detect it by eye.

 

my friend had the same problem,and had to install new main bearings. his wasn't leaking,but he noticed to much end play while replaceing the clutch.

 

You don't have to install all new main bearings, unless you want to. Cummins does sell a new thrust bearing in several sizes, std, .010, .015 and.020 I think they are. Automatic trucks don't put much of a thrust load on the crank and the thrust bearings last much longer, usually as long as the engine does. A manual trans truck is another story all together, they may go through two or three thrust bearings in sever duty before the engine needs to be overhauled.

I would put a dial indicator on the crank flange or snout and see how much you really have before condemning the thrust bearing. Most likely the crank snout has a grove warn into where the seal rides. If this is the case you can put a speedi sleeve on it to restore it to like new condition and give the seal a good surface to ride on.

 

yep your right,you don't always need to change all main bearings,but his had over 300,000 miles on them and he decided while he was at it that he would change them all. I think he changed the rod bearings too.

 

Well we got the endplay checked today. It's not as bad as as I first thought. We checked it a number of times and depending upon position of the magnetic base it was .012" to .015" so it's definately at it maximum allowance. I ordered a Cummins seal yesterday so the first plan will be to see what happens when I replace the seal. Second plan is to get a main thrust bearing ordered and put it in this coming Summer.