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Topic: M-11 Exhaust Manifold (Read 1455 times) previous topic - next topic

M-11 Exhaust Manifold

Well, I just left a few coach bucks in Boise.  Looking over the engine for anything that looked amiss, I noticed black soot on the side of the head next to where the number one and two manifolds bolted on.  Then I realized that the two bolts for the number one cylinder were missing.  Actually they had fallen out and were wedged in a nook down below.  The gasket was completely gone. 

I was at the Gowen National Guard base at the time and thankfully there was a Cummins coach care facility less than three miles away.  The exhaust manifold on the M-11 is in three pieces, the center section with the turbo covers the middle four cylinders and separate pieces cover number one and six.  To remove any piece all three must come off.  On examination, the mating surface for the number one and two cylinders were quite pitted so I opted to replace the entire manifold. 

The mechanics there could not explain what might have caused the two bolts to break but said it sometimes happens. 

Richard
Jan & Richard Witt
1999 U-320  36ft WTFE
Build Number: 5478 Motorcade: 16599
2011 Jeep Wrangler Unlimited w/Air Force One
Jan: NO5U, Richard:KA5RIW
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Re: M-11 Exhaust Manifold

Reply #1 –
Exhaust manifolds usually have small ears where the studs/bolts go but your manifold has long bolts. Any shrinkage of the manifold may allow the bolts to vibrate and then crack. This is also found in diesel fuel injection pipes where owners remove the small bracket that ties all the pipes together. They pick up a resonance and will crack inside the nut that secures them to the pump. The original 8.3 exhaust manifold were prone to shrinkage and cracking. The design looked to be out of the 1800's.

Your M11 exhaust manifold looks to be an excellent design to avoid cracking and may only need to have the bolts checked for torque occasionally.

Looks like the turbo was replaced some time in the fairly recent past.

Pierce
Pierce and Gaylie Stewart
'93 U300/36 WTBI
Detroit 6V-92TA Jake
1140 watts on the roof
SBFD (ret)

Re: M-11 Exhaust Manifold

Reply #2 –
I recently replaced the gaskets on our M-11.  I no longer have a loud hissing noise when I drive near a wall!  The coach was new to us, so I didn't know what to listen for.

Our coach had a black smudge around the cylinder #1 manifold connection.  Not the kind of thing one would notice with a casual look-over, but conspicuous with a good flashlight and an inspection.
Matt B
1998 u-320

Re: M-11 Exhaust Manifold

Reply #3 –
Richard

Could have the bolts drilled for safety wire and re-install. Then Safety wire will ensure they don't loosen, vibrate, then crack.
Future Foretravel Owners
2019 Jeep Cherokee Trailhawk
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Larry and Becky Rountree

Re: M-11 Exhaust Manifold

Reply #4 –
Quote from: master2301 –
Could have the bolts drilled for safety wire and re-install. Then Safety wire will ensure they don't loosen, vibrate, then crack.
When/if the manifold shrinks, the distance/thickness of the manifold becomes less from the shoulder of the bolt to the mating surface on the cylinder head. The bolt will not turn but also will not shrink with the manifold so will become loose over a period of time. So, the safety wire won't do any good since their is no rotation of the bolt.

Pierce
Pierce and Gaylie Stewart
'93 U300/36 WTBI
Detroit 6V-92TA Jake
1140 watts on the roof
SBFD (ret)

Re: M-11 Exhaust Manifold

Reply #5 –
My theory #1 is that the long bolts are used to allow the expansion and contraction of the manifold to be distributed over a longer area - several inches on the M-11, versus maybe 1/2 inch of bolt or stud outside the head on other styles.

My theory #2 is that the breakage often results from not letting things cool down a bit after a heavy run.  In my case, and others I have read, the bolt binds in the manifold holes, reducing the amount of bolt available to stretch.  In my case, the holes in the manifold were packed with debris and rust, and the amount of torque to remove the bolt did not change much when the bolt was "loosened."

Upon reassembly, I was shocked how low the torque spec was for the manifold bolts.  I imagine it is A LOT more when the engine is hot.
Matt B
1998 u-320

Re: M-11 Exhaust Manifold

Reply #6 –
Cummins learned their lesson from the 8.3 one piece exhaust manifold. It would shrink about 3/8" and bend the fasteners that then would break and also crack and break the ears off the manifold. The M11 manifold solves this being made in three pieces so the pieces slide to accommodate any shrinkage. There are also stainless studs available. Good info here: https://talk.newagtalk.com/forums/thread-view.asp?tid=3540&DisplayType=flat&setCookie=1  The cracked exhaust ports are not a pretty sight.

Your theory #1 and #2 may also be not far off the mark. Might pay to use Never-Seez on the threads for installation.

Pierce



Pierce and Gaylie Stewart
'93 U300/36 WTBI
Detroit 6V-92TA Jake
1140 watts on the roof
SBFD (ret)

Re: M-11 Exhaust Manifold

Reply #7 –
Richard good catch and resolution IMO. how many miles on the clock?
Scott

Re: M-11 Exhaust Manifold

Reply #8 –
Quote from: dsd –
how many miles on the clock?
Scott
My coach has just under 160,000 miles. I suspect that the manifold bolts have been broken for some time.

It might be a good idea to use a flashlight and look for black soot around your exhaust manifold. The problem is not one that will leave you stuck on the side of the road but is certainly one that should be addressed.

Richard
Jan & Richard Witt
1999 U-320  36ft WTFE
Build Number: 5478 Motorcade: 16599
2011 Jeep Wrangler Unlimited w/Air Force One
Jan: NO5U, Richard:KA5RIW
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Re: M-11 Exhaust Manifold

Reply #9 –
I believe this is an issue to catch early.  I got lucky.  If the issue persists, the exhaust erodes the sealing area of the manifold (bad) and/or the head (badder!).

I was able to replace the gaskets myself without disconnecting the rest of the exhaust.  Not easy, but easier.  The thread is around here somewhere.
Matt B
1998 u-320