hump hose moves - why?

[Ron Hill]

Randy : Try the RTV Hi Temp sealant.  Just go to any automotive store and they'll sell you some. 
Then tell them what you are sealing.  If it's the threaded riser into the exhaust flange they'll probably tell you to use muffler paste - as that exhaust is HOT!!  After the raw water enters from the nipple and mixes with the exhaust gas - all cools down considerably!
Your boat - you make the choice.   

[Randy and Mary Davison]

Hi Ron,

The job's been done for several weeks.  Stu asked me earlier in the thread what I'd used.  It was a high temperature sealant recommended by my local diesel repair firm - North Harbor Diesel - but my aging memory can't remember the name and haven't been back to the boat yet to look at the tube. 

Randy

[Randy and Mary Davison]

This is my last - I hope - posting on my project to stop the play in my exhaust riser.  the purpose of posting this is for the benefit of future searchers.

After pulling the system apart the first time, I sealed the flange to pipe threaded connection with a product called Acousti-Seal, recommended by my local marine engine repair shop.  Put the system back together with the old "non-hump" hose place - all worked and there didn't seem to be any play.  Meanwhile, I ordered the blue hump hose from Catalina Direct with the intent of cutting away the old hose and using the flexibility of the new one to avoid pulling the system apart again.

You can guess...as soon as I put any real pressure on the riser it moved a few thousanths again.  I pulled the riser assembly back off, thinking my sealant had failed.  What I found was that the motion was at the other end of the short threaded pipe that goes from the flange to the stainless portion of the riser.  The flange to pipe seal was solid.  I had tried to unscrew the pipe section on the first removal but couldn't get it to turn with moderate force.  This time a really reefed on it and it came unscrewed.  The threads were good so I sealed the riser end of the pipe with Accousti-Seal and put it all together with the new hump hose installed.

It's completely solid now so I'm pretty certain the problem is solved.

I don't know how the pipe could move a bit in it's threads and still be that hard to unscrew.  It went back together with no problems such as being out of round.  The lesson is to make sure to get that short section unscrewed from under the wrapping and seal it along with the flange end.

Other notes - you can remove the riser without going through the aft cabin although cleaning the manifold flange mating surface is easier from the back.  I did it all from the front on the second removal.  Total project time for the second removal was 4 hours including cleanup. 

The drain plug on the aft end of the manifold would not come out so I opened up the end of the heat exchanger and also used a PAR hand pump to be sure all of the coolant was removed from the manifold so it doesn't run into the engine when the exhaust gasket is removed.

Thanks to all here for suggestions along the way.