Exhaust Manifold- ONAN 7.5 MDJE 3CR 2268 AC

[Genevatexan]

I need an Exhaust manifold for my Diesel ONAN MDJE. The Cummins Diesel part number is 154-2122, which superseded the original part number 154-1058 for the heat-exhanger version of the manifold.

The end where the nipple and Exhaust elbow attach is rusted out. The inner threads where the 1 1/4" nipple threads in are rusted out.

Any help here appreciated, or ideas on how to patch up. I have ordered the exhaust elbow and nipple already (completely rusted out), but need the manifold, or some creative ideas on how to deal with the rusted out end....

Thanks,
GT

 

[Avenger]

Do you have enough material in the manifold to tap it to 1-1/2" and use a reducer bushing?

 

[sgharford]

Just a thought, I've seen a couple of MDJE's sold for parts on Ebay from time to time, maybe contact the seller and see if he will sell you manifold. Problem is you may wind up with one that is pretty shot as well. It’s a crappy job, especially if you have sound shield. If I recall correctly, front flywheel cover, belt guard, heat exchanger and starter have to come off to get at manifold nuts. There are special round gaskets between block and manifold you would need to replace at minimum. All my studs were shot, so I added new studs, nuts, and special nut locking tabs (have fun undoing the originals with a long screw driver and hammer) - so something like $100 in parts and shipping, plus cost of manifold. I did a bunch of other stuff while in there, but I'd say it's a 4 hour job if everything goes relatively smooth (so give it 8). With that said, find a good quality replacement when time comes.

 

[Boatsb]

Just a thought, I've seen a couple of MDJE's sold for parts on Ebay from time to time, maybe contact the seller and see if he will sell you manifold. Problem is you may wind up with one that is pretty shot as well. It’s a crappy job, especially if you have sound shield. If I recall correctly, front flywheel cover, belt guard, heat exchanger and starter have to come off to get at manifold nuts. There are special round gaskets between block and manifold you would need to replace at minimum. All my studs were shot, so I added new studs, nuts, and special nut locking tabs (have fun undoing the originals with a long screw driver and hammer) - so something like $100 in parts and shipping, plus cost of manifold. I did a bunch of other stuff while in there, but I'd say it's a 4 hour job if everything goes relatively smooth (so give it 8). With that said, find a good quality replacement when time comes.

well stated.

forget the used manifold idea.

 

[captddis]

It is just a pipe nipple!!!! Take a punch and punch it in until it pulls away from the manifold and pull it out. I do them this way all the time.

 

[Avenger]

I got the impression that he means the female threads in the manifold are shot.

 

[Boatsb]

I got the impression that he means the female threads in the manifold are shot.

If that's the case the manifold can probably be brazed and re threaded for about the same cost as buying a new one. I had a bad end cap on my 8v53's and could not locate a replacement at the time. Thank G-D for good machine shops.

 

[Avenger]

That's possible too. I was trying to find a Heli-Coil kit for it but they don't seem to make them that large, or at least the conventional machinery supply houses don't list them.

 

[captddis]

I got the impression that he means the female threads in the manifold are shot.

You can see the nipple sticking out. The elbow is just an off the shelf plumbing part.

 

[gbharrington]

I am buying an MDJE for the back end and will part out the rest. I should have it in my posession next week if that works for you.

 

[gbharrington]

I am buying an MDJE for the back end and will part out the rest. I will have it in my possesion next week if that works for you.

 

[Genevatexan]

I thought the piece on the end of the manifold WAS the manifold. If Captdis is correct and it is just a threaded pipe tapped into the end of the manifold, the short answer is to knock it away from the threads and see what's left. I did not understand that was not part of the manifold and the inside of that pipe is completely corroded away. Since the two pieces (manifold and elbow) were joined by an asbestos wrap in a rigged setup, i assumed there was no remaining nipple.

Let me get up there and give it another go. I have a new nipple and elbow coming, that are correct to the unit, but do not match what came out, supporting the idea that the old elbow is a bog-standard plumbing part. if I can knock out the bad nipple and thread in new nipple and elbow, I'm in, with the exception that the outlet of the new elbow is 1 1/4 and the rubber exhaust hose to the thru hull is 1 5/8, I believe. I also think the outlet on the new elbow is smooth and not threaded. Is there a good way to bush that up to the 1 5/8 flexible hose?
Thanks for the guidance,
GT

 

[Avenger]

Well, you said internal threads and seemed to know what a nipple was so I figured you'd already gotten the nipple out of the manifold. What I get whan I assume.

Good luck with the repair.

 

[Genevatexan]

Scrod,
My bad, it was cruddy enough that I could not tell what it was and thought it was really part of the actual manifold. The outer edge appeared smooth like a finished part of the manifold and was clamped around the OD with a hose clamp.
All advice appreciated, without this dialog I would have pulled the manifold.
I'll try to knock the nipped down from the threads and rebuild connection. New nipple arrived today, it looks like a good match for threads for both ends assuming I can save the manifold. Awaiting elbow now ($149). If this works its going to save me ALOT of work.
GT

 

[Genevatexan]

Re: Exhaust Manifold- ONAN 7.5 MDJE 3CR 2268 AC- Saga continues

The nipple fell off in my hands when I got ready to drive it off the threads in the manifold, rusted through. the manifold is messy on the end. depending on cost of a used unit, finding a machine shop to tap, or cut it to oversized threads may be more work than necessary.
Two questions: if you look at the photos, the manifold has two ends for exhaust (one is plugged) and appears to have tappable holes on the opposite side for the closed cooling connections. Could this unit be reversed, tapped on the two closed holes on the bottom, and one end welded up and the other used for the exhaust? It looks like it may be reversible, and tappable.
GT

 

[Genevatexan]

View attachment 10782


And here is the view where you see what appears to be tappable connections on the back side of the Manifold...

 

[captddis]

It still looks like the remains of the nipple can be peeled away with a nice sharp chisel. Maybe slice the nipple in two with a hacksaw too.