OldIHC

I'm having trouble getting a good seal from the exhaust header to the pipe that sweeps back. Replaced the exhaust flange gasket years ago, then tried again with some sealant, but no amount of tightening will make a good seal. Is there an extra thick option available? I've seen some on Amazon that are .2 inches thick, but not sure of fit. Do you know exhaust hole diameter and the bolt spacing?

Thanks

I don't know why you would ask about the measurements, you have your truck with you. Why not measure what you have? This is not the time to get aggressive with the tightening. Those old castiron flanges have been heat-cycled thousands of times and will have become nearly as brittle as glass.
My best advice is to make the contact surfaces as smooth as is possible then use a reasonable torque and an exhaust heat resistant gasket material to make the final seal. I do not know what you level of tooling is, but, if you have a lathe you might be able to make a sleeve that slips inside the manifold and the tailpipe to help with alignment and sealing.
On our original R120 with the 220SD, I did not use a gasket at the connection to the tail-pipe. I made and used a doughnut ring that fit a taper in the manifold and I had the muffler shop put a slight flare in the down-pipe. Our 220SD had 3 inch pipe at the manifold connection and all the way to behind the right rear fender. I installed a https://www.magnaflow.com/ muffler.
If you turn the exhaust out to one side your truck will not have the situation of following exhaust getting into the low pressure area behind the tailgate and wafting over the truck when you stop.
I never put any exhaust out the back. Our 1940 Fat Fender Ford design carries a low pressure area behind the trunk lid. Without a 100% seal, there will be exhaust fumes in the car. I built a custom canopy for our R120 and this added to the low pressure area. I had the exhaust turned out behind the left rear fender. The engine was an idi Diesel and smoked a little. You do not want the $hit in your cabin.

That material they use to seal wood stove doors will form to an irregular surface.
They sell it in a round or flat material that looks like asbestos rope. I have used it along with plenty of copper coat sealer to hold in place and help it seal.
I used it when a doughnut gasket wouldnt seal. It compresses well.
https://www.fireplacedoorsonline.com/fl ... asket.html

bring your old 1 in the a muffler or auto store to get the correct one. Worked for me, mine was 2-1/2" X 1/2", three bolt flange, there are many sizes.

It looks like I need an exhaust flange donut. Mine is split, probably from cranking it down too hard and trying to get a good seal. I did spend some time looking around for options for gasket and donut(muffler shops, NAPA, Advanced auto)- no luck. Last place I purchased exhaust gasket was Tractor Supply Center, however they've stopped carrying a lot of parts. I need a tapered ring 2.25 inches inside diameter, and I'd like something soft to make a good seal. NAPA has lead, but not tapered enough to squeeze in. I think I found an option on Amazon so will see how that works. I'm also wondering if I need spring bolts holding the flanges together when I finally install a donut.

Thanks for the fireplace gasket tip. I did play around with that a little bit, but didn't have any luck. Only cost me $6 for gasket kit at Menards.

check out this on Rockauto.com http://www.rockauto.com/en/moreinfo.php ... 18&jsn=436 WALKER 31394 2.25"; Sintered Iron Material

When you install the new one its best not to have the whole exhaust hanging there. Yuu need to be able to get the doughnut in place and tourq the bolts down evenly keeping the flange square with the manafold.
If you already know all this ,disredaurd .

I ended up trying multiple variations- donut ring with gasket, two gaskets, spring bolts, etc. What finally worked was a 2 inch inside diameter ring (Walker 31416 Exhaust Gasket) with no gaskets. This ring is tapered on both ends so it centered up btwn both flanges. I ended up with some Grade 8 bolts and tried not to torque it down too much.

In this application a grade 8 bolt will not be able to be torqued enough to make the bolt stretch. A grade 5 will stretch at a much lower torque and should help to remain tight over the heating and cooling of the connection. While grade 8 are very strong this is not an application for using grade 8. I would not be surprised if the OEM IHC bolts were grade 5. Longer bolts with springs were popular back in the day.
On our R120 with a 220SD, I made a triangle bracket that used three oil-pan bolts on one end, while the other end was bent up at approximately 90 degrees so I could attach an exhaust clamp. This was to help to keep the down-pipe moving with the engine and reduce strain on the manifold connection.