Offset Exhaust Manifold Adapter 766 w/ C291 Gas

[Ron 766]

Restoring 1972 766 with C291 gas engine. I need an offset exhaust manifold adapter to fit the large exhaust manifold in order to align the exhaust pipe through the hood panel. It is currently 2 inches off. I can find offset adapter for the smaller engines but nothing for the C291. Thank you for your help! Ron 766

[billonthefarm]

1 hour ago, Ron 766 said:

Restoring 1972 766 with C291 gas engine. I need an offset exhaust manifold adapter to fit the large exhaust manifold in order to align the exhaust pipe through the hood panel. It is currently 2 inches off. I can find offset adapter for the smaller engines but nothing for the C291. Thank you for your help! Ron 766

  I looked for one for my 766 a few years ago without any luck.  When I get ready to restore it I guess I may have to make something unless you find a source.  Good luck and keep us posted.

[Tobaccoman]

Get a couple of 45 degree pipe elbows and a couple or 3 pipe nipples of the right length and you should be in business. That's what I did on my 656 a few years ago. I used 2 inch but since you said large, the 766 may take 2 1/2 inch pipe.

[Ron 766]

I ended up cutting exhaust pipe at 22-1/4 degree angle to get it aligned with the hood panel. Thanks for your post.

 

[brahamfireman]

What's your plan for when the threads loosen up,  because they WILL loosen up. 

[HydroTek]

766 gasser used a flange to connect to the manifold
the flange was easily bent  -- hitting limbs and just normal vibration

Welding on a flange now before the threads loosen up would be a plus to the new adapter 
just slip the flange over the pipe and weld in place 

[Diesel Doctor]

On 9/7/2025 at 3:48 PM, brahamfireman said:

What's your plan for when the threads loosen up,  because they WILL loosen up. 

Yes, those originally were bolted to the manifold, as were the propane's to get the exhaust ahead of the LP tank.

 

[Mike56073]

On 9/7/2025 at 3:48 PM, brahamfireman said:

What's your plan for when the threads loosen up,  because they WILL loosen up. 

On my 656 gasser that did that, I welded a nut on the bottom of the pipe right above the threads, then lockwired it from the nut to the exhaust manifold. It's been that way for years now.

[brahamfireman]

3 hours ago, Diesel Doctor said:

Yes, those originally were bolted to the manifold, as were the propane's to get the exhaust ahead of the LP tank.

 

My 706 propane screws in, ****** me off, I wish it was bolted. 

[snoshoe]

Many years ago there was a service bulletin concerning loose exhaust pipes. Seems an exhausting study had determined they were not tightened enough. Best I can remember I think 100 lb ft was specified. Nowhere near enough. Soon we were putting M+W turbos on 8s. The screw in adapter under the turbo kept coming loose. I acquired a 24" chain wrench. Using that and the 4 foot pipe that came strapped to the frame with new tractors. I was able to solve that problem. Applying it to the older tractors that had been loose awhile. I found an application of moly grease to the threads and pulling on the pipe as hard as I could that it would hold. As long as thread would start no cleaning or tap was necessary. Never broke a manifold or had one come loose that I ever heard of. Had one SM that manifold hole was so worn out that pipe bottomed inside manifold. Had to replace that one.

Do not know how tight I was actually tightening them but have torqued enough wheel bolts to know it was at least 400 lb ft on a bad day. The moly is important. If pipe is to burnt out. It will collapse.

[brahamfireman]

2 hours ago, snoshoe said:

Never broke a manifold or had one come loose that I ever heard of. Had one SM that manifold hole was so worn out that pipe bottomed inside manifold. Had to replace that one.

My 756 gas was like that, so wore out it was sitting down inside manifold flopping all over. I had the neighbor braze it up/solid.

[Matt Kirsch]

15 hours ago, snoshoe said:

Seems an exhausting study

I see what you did there...