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Old 10-14-2021, 09:33 AM   #1
Senior Member
Holiday Rambler Owners Club
Join Date: Apr 2020
Location: Farmington Hills, Michigan
Posts: 412
Exhaust pipe replacement on 2004 HR Imperial w/ISL 400

I got a hole in the exhaust pipe just below the first 90 deg bend down after turbo (I assume original Holset turbo).
FleetPride did not have this 3.5" pipe from turbo, only 5" dia elbows etc. Cummins said they do not provide those pipes, REV response was perhaps "PIPE TURBO EXHAUST ALUMINIZED 4IN TO 5IN Part # 10123042" but no details. I also heard from a diesel mechanic that those can be difficult to find.

So ended up cutting the turbo end of the pipe after the flare to 5" dia and had a truck shop weld that to a new shortened 90 deg elbow. I had to do this to get the pipe routing to fit, similar to the old pipe.

Does anybody have a source & pn. for this 3.5" (4" at turbo mating face) to 5" pipe should this pipe fail again?
The old pipe had been cut in a slight angle and welded but I don't know if that was original Monaco or Roadmaster design or something a previous owner had done.
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2004 Holiday Rambler Imperial 40PKD, Cummins ISL 400
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Old 10-14-2021, 04:39 PM   #2
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Monaco Owners Club
Join Date: Oct 2009
Location: On the road
Posts: 1,872
This place has your flared reducers...

All these coaches were pretty much custom pieces or at least changed almost every year, and different for each series of engine. Pipestore has all you need to make up a new one.
Happy Trails,
06 Dynasty Countess III ISL//3060
07 Hummer H3
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Old 10-15-2021, 04:35 AM   #3
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Monaco Owners Club
Join Date: Jul 2018
Posts: 98
Here’s some info on exhaust parts.

Maybe for you or anyone looking at doing something in the future.
05 Dynasty Platinum IV ISL 400
It the journey not the destination!
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Old 10-15-2021, 11:37 AM   #4
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Holiday Rambler Owners Club
Join Date: Apr 2020
Location: Farmington Hills, Michigan
Posts: 412
Thanks for the info.
I did look at some other pipe supplier sites but did not find a complete formed piece. Looks like it has to be built with clamps from individual pieces right from the turbo flared connector.
I did not have much time to get this done as the coach was on my driveway without exhaust and we have very limited HOA and city ordinances how long it can be there. I was not going to put the old one back with the hole in it.
The diesel mechanic who welded the pipe said that the preformed clamp (in my original pic) may not hold on the vertical piece and suggested a guillotine clamp. So I changed to that on my final installation once I got the routing and angles set up.

In hindsight knowing all that, I should have gotten all the pieces first and use clamps on the first horizontal pieces. This would have allowed me to adjust the vertical section as the pipe out of turbo was in a slight angle and had to be remounted in the same exact orientation. So the bottom end of pipe ended up very close to the frame.
2004 Holiday Rambler Imperial 40PKD, Cummins ISL 400
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ace, exhaust, replace, replacement

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