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Topic: M-11 Oil Pan Threads (Read 364 times) previous topic - next topic

M-11 Oil Pan Threads

During an oil change, the threads in the oil pan drain of our 1998 U-320 came loose.  This is apparently a common problem with the Cummins M-11, because it has a steel drain plug and an aluminum pan.  If your pan threads have not failed, it might make good sense to replace the drain plug with a Fumoto valve, a No Spill or other drain device.  One time and the treads will be preserved.

This issue has been addressed in several threads, but information was incomplete.  There seemed to be room for a procedure.  Other people have taken different routes for a remedy, and I respect that.  Likewise, I welcome your comments on corrections, amplifications, etc.  It is all about us leaving a nice trail for other forum members.

It took some research to find the details necessary to repair the pan with the Cummins-supplied repair part 68749.  It comes with no instructions, nor could I find instructions online.  The part is a threaded plumbing-type  adapter.  The inside is threaded with one-inch machine thread.  The outside is one-inch NPT at 11.5 threads per inch.

The adapter could be installed more easily with the oil pan removed, but that requires a new gasket, the removal of LOTS of bolts, and additional chance of introducing dirt and debris into the engine.  I chose to install the adapter with the oil pan in place.

Here is my procedure:

1.  Inspect the drain hole for cracks, chips or other issued that might make it unsuitable for continued service.

2.  Liberally grease a 1-5/32 drill bit, and drill the hole out.  (Other people have used a 1-1/8 inch bit with success.  The bit hung up and bucked a lot.  This might be a good application for a stepped drill bit.)

3.  Using a finger, feel inside the pan through the hole for chips.  There will be a few.  They are non-magnetic, so a magnet is of no use.  Clean any chips from the hole surface.

4.  Use a NPT Tap, 1"-11 1/2" (1907ZR) to thread the hole.  Note that the Cummins repair manual specifies a 1-inch NPTF for chasing spoiled but serviceable threads.  This might work better, but I do not know that.  I could not find a source for one.

Carefully start the tap.  Thread it in about one half turn, and out a quarter turn to keep the new thread way clear.  I removed the tap at about 1/3 completion and 2/3 completion to check the threads with the adapter.  Do not work the tap completely into the oil pan – I imagine it very difficult to realign the threads to remove it, should it fall in!

5.  Clean the area thoroughly, including the accessible part of the inside, removing all fragments.  An ungloved finger is very good for feeling the bits.  Paper towels are good for sopping up the residual oil.  Cloth does not dissolve well in oil, so I have been told.

6.  Remove the side plug from the pan.

7.  Using a fluid transfer hand pump, spray a quart of oil into the pan.  Again check the inside of the pan for fragments.  I found one large additional fragment.  Repeat two more times, or until no fragments are found.

8.  Use a borescope and flashlight to visually inspect the inside of the pan for fragments.

9.  Replace the side port plug, after cleaning and applying RTV.

10.  Clean the insert thoroughly with brake cleaner.  Clean the chosen drain plug or valve with brake cleaner.

11. Install the plug into the adapter.  Use Loctite red if the plug is semi-permanent.  Consider anti-seize if conventional

12.  Carefully install the adapter and plug into the carefully cleaned pan hole.  Snug up with a socket on the plug or valve.  Don't go crazy – we are still threading steel into aluminum.

13.  Liberally apply Loctite 290 to joint between the adapter and the pan.  It is designed to wick into already assembled parts.  Let "dry" for minimum of 20 minutes, preferably 24 hours.

14.  Refill oil and check for leaks.  I added just a couple of quarts for a quick leak check.
Matt B
1998 u-320