inline 6 exhaust flange ("donut") frequently failing

[cell]

So I have been having a recurring problem with my 292 inline 6. Where the exhaust manifold connects to the exhaust pipe, there is a circular flange (a "donut") and it has been failing about once per month. And when it goes out -- boy this truck is as loud as a dragster.

Has anyone else experienced this? Maybe my engine mounts are going out and the engine is moving too much, putting strain on that flange? Maybe my exhaust pipe is mounted too securely (maybe I need more of those exhaust hangers with rubber joints?).

I just recently learned to weld, so I think ultimately my solution will be to create my own set of headers.

sorry no pics -- its late (or early...).

['68OrangeSunshine]

I have a set of Clifford headers on my 292, so I don't remember that problem. I've been running the headers since 1978.
If you are having excess vibrations, you might check on the health of your harmonic balancer. A wobbly damper can throw a lot of things out of kilter, especially on these L6s. Over-revving (going over the redline at [only] 5000 RPM) can foul up the HB.
Before I had a shop weld up a set of dual exhausts -- back in my college days -- I had a pair of steel packs pushed into the header collectors and held up in back by bailing wire. Sometimes when crossing rural rail tracks, things would come loose. The headers would get loose and performance woud begin to suck.

[GruntyPants]

How is the donut failing? Does turn black and unravel? I had that happen on my '69 Vette and it was because it was running WAY rich. You can specify a solid steel donut that might help out.

[cell]

very interesting grunty -- as a matter of fact that is exactly how it is failing, and my carb (a single bbl rochester) is permanently jetted too rich (apparently torque was more important than fuel economy back in the day).

I never would have considered that a rich mixture could have been the culprit. Thanks for the suggestion.

[Brad]

Originally Posted by cell

very interesting grunty -- as a matter of fact that is exactly how it is failing, and my carb (a single bbl rochester) is permanently jetted too rich (apparently torque was more important than fuel economy back in the day).
I never would have considered that a rich mixture could have been the culprit. Thanks for the suggestion.

, interesting. I never would have guessed. Anyway, I've had some problems in the past with that and always thought it was a leak in that area and that the tailpipe wasn't aligned properly with the exhaust manifold along with being too rigidly held in place.

[68GMC454]

my chevelle used to blow out the donuts all the time..but this happened to me because the new dual exhaust i had was from a freinds camreo and they didnt exactly line up right. they cross members were different fromthe camero and chevelle,,i could put in new dountus, and be alright for miles,,bu tthe first time i got on it, i would blow them out. i finally just quit putting them in..maybe you pipe and the header are slightly out of line..they need to be straight and level...if slightly out of line you can blow them out...check and see if your pipe hangers are still good...
billy

[da-burb]

If you are using the compressed fiber and metal doughnut you might want to try the all metal version. When I had my 65 Impala I was having the same issue and changed them out to solid and never had the problem again. That was with a V-8 but it should still relate.

On a side note...is this the possible reason why some of these I-6 manifolds have 3 studs vs only 2 at the flange?

[BCOWANWHEELS]

heres how you fix the problem,
add a exhaust pipe mount off the engine to bellhousing mounting bolts. takes all the stress off the exh. pipe and doughnuts will last forever. been runnin I-6,S forever. old man taught it to me......
bob

[Big D]

I agree with Bob, I bet your exhaust pipe is flexing while you drive, which causes the donut to fail. This is one reason why all the newer stuff uses a 3 bolt flange. It doesnt allow the pipe to swing as much.

I fought the same battle with my 70 GMC w/250 six. It only had 1 hanger before the muffler, I added 2 more and the problem went away. Now if I can only get the exhaust manifold to seal to the head I'll be a happy camper.

[2bits]

That's good info for me to stop a problem before it happens on mine! Thanks!

[cell]

great replies guys -- thanks!

[cell]

funny, turns out the solid metal donut was even cheaper than the compressed fiber one. next time it blows i'll give it a shot.