Exhaust Leak - Onan 7.5 Diesel Genset- at the manifold

[Genevatexan]

I was servicing the genset last weekend and fired it up from the bilge after an oil change and fuel filter change. It has developed an exhaust leak at the joint where the manifold goes into a pipe that later feeds the through hull pipe. This union is behind the Genset, and right under the salon sole and against the bulkhead. It's hard to see, but it appears to be a fiber or asbestos packing that then goes into a metal collar, inside another collar, that then exits to the flexible exhaust hose that runs to the thru hull.

I still need to get pictures but after checking history have not found a direct match for a similar problem. Can someone guide me on how this union is constructed and what parts I will need to repair? On startup its blowing exhaust off the leak into the bilge compartment, and then seems to go back (more or less) to exiting normally. Not good.

GT

 

[BUSTER]

If it is wrapped with fiberglass it is apparently (before) the water injected and cooled elbow, which is joined with the rubber exhaust hose. It is quite possible that it is just a loose threaded pipe joint,but you won't know until you remove the insulation and have a look. If it is very tight you may need a mirror and a light to see it as someone starts the unit while you take a look.

 

[delta]

If there is a removable panel in the cabin sole above the generator access will be a lot easier. Recently had the same problem with a 81 model and was able to get factory replacement parts without any problem.

 

[Genevatexan]

The exhaust union looks like a jerry-rig. I got back in there and found the elbow joined to the engine manifold (ONAN 7.5 Diesel MDJE) with what looks like an asbestos wrap that joins two pipes of different diameters. The flange on the exhaust manifold looks like 1 5/8 and the exhaust elbow OD is 2 1/8 and the ID looks completely jacked up. (see pictures). I am guessing that there was a threaded pipe with OD 1 5/8 threaded into the elbow that gave up. so the FO just mated the OD of the elbow with this flexible material and necked it down from 2 1/8 to 1 5/8 with this material.
So question 1, does someone have the elbow they would part with for a fair price, and 2) can I assume that perhaps I could work the old portions of the threaded pipe out of the elbow and try to revive it?
See attached pics.
Thanks
GT

 

[Genevatexan]

trying to add picture of the packing

 

[rjdebellis]

I am new to this forum and am experiencing the same problem. It appears that the elbow coming off of the exhaust manifold that connects to the hose that goes to the exterior is cracked. I bought the boat 6 months ago and getting ready for a cruise and smelled diesel exhaust in bilge along with bilge pump going on. How does one get that elbow off as mine is severely rusted?

 

[Genevatexan]

The best approach is to remove the exhaust manifold first. The bolts that hold it to the engine came out surprisingly easy, probably because the manifold is water cooled. Otherwise I would expect it to be brittle and bolts to shear at the block. Those bolts are on the back side and can be easily removed. You must remove all the hoses and then disconnect the large hose to the elbow and remove the assembly. I think I removed the heat exchanger tank for better access. Its an hour or two of work, easy to do, just cramped in our boat. My manifold was badly rusted and the connecting pipe that threads into the manifold and elbow was shot. The elbow in my pictures above was also from a plumbing shop, not the Onan OEM. I took my manifold and had a hot rod shop put it on a cylinder boring press and bore it to the original threads. They were very good, and it ran me about $200. In the meantime, I bought a backup, which I still have. Private Message me and I will cut you a good deal on it. Then you must buy the threaded coupling, and probably the elbow and quickly re-assemble. The elbow includes a high temp cutoff switch connection, which I highly recommend reconnecting. Mine was completely disconnected. Don't run your engine with that leak, it could easily take you out. Beware of used manifolds, the owners will try to sell you those with ruined threads, rusted connections and the original threaded connector stuck in or broken off in the manifold. Almost all of these older onan manifolds are shot, and simply require a smart and savvy machinist to save them.