Exhaust doughnut

[udidwht]

I replaced both exhaust dougnuts before my return trip home (HB,Ca. - Renton, Wa.) and the passenger side one started getting noisy again when close to home. Crawled underneath and I'll be damned the doughnut on the passenger side is nearly gone after roughly 1400 miles. Wondering if an flaky EGR can cause this. This RV has 454 with electric driven EGR on the passenger side of the engine below the air cleaner housing. This issue popped up while in southern Ca. and I bought (2) Fel-Pro Duralast doughnuts and replaced both. The passenger side one was completely gone except for the metal ring the gasket is attached to. Roll forward 1400 miles the same gasket is again having to be replaced. It still has some gasket material around the metal ring but not much.

One other thing I noticed...prior to removing everything the bolts the hold the flange up seem to bottom out on the threads before cinching down on the springs. Of the (3) bolts one of the springs could easily be moved up/down and or spun once tightened. I'm thinking the bolts did not tighten enough and air drawn in eroded away at the gasket. The drivers side looks great after the return trip.

Vehicle is in signature.

 

[Frank Enstein]

if it wasn't tight enough or dirty it will kill a donut gasket very quickly.

Clean both metal surfaces until brake cleaner on a white paper towel stays white.

A smear (too much will have rings of silicone bouncing around in your exhaust) of sensor safe silicone can fill the imperfections in the metal and gasket surface.

Don't let it skin over and assemble slightly more than finger tight and let the silicone cure overnight if possible. In the morning (after coffee) complete tightening of the bolts/studs and it should be fine.

Not a big fan of springs on the flanges but I would tighten the springs until they were nearly coil bound. Warm it up and let it cool down a few times (without driving it) and retighten the bolts when cool.

 

[man-a-fre]

Did it have the steel insert in the middle of the donut if not thats probably why it went out.

 

[kennythewelder]

Also FYI they make a steel donut gasket. These do not blow out. I have a set in my 97, 5.7L. I had to ask for them for a 1972 c-10 with a 350. You may be able to do the same thing with a 454 from the early 1970s.

 

[udidwht]

Did it have the steel insert in the middle of the doughnut if not thats probably why it went out.

Yes it did. Not much of the actual gasket material left. It was circular still but 90 percent gone. I finished replacing the gasket. It turns out the springs compared to new ones were 1/4in+ shorter allowing for the nuts to bottom out before applying the needed tension for the flange. I replaced all the springs and nuts and used plenty of copper seize.

Checked the one on the drivers side and it still looks new after ~1400 miles. Replaced the springs and nuts on it as well. Lots of copper seize. Now I'll let it run a few at idle then cool down and check everything.

 

[udidwht]

Here's a pic of the doughnuts from the passenger side. The one on the left was the original one I replaced while on my trip in southern Ca. The one on the right was the new one that replaced it after ~1400 miles home. I should have replaced the spring and nuts the first time. Lesson learned.

20210716_233244_LLS[1].jpg

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[man-a-fre]

I here ya , I had a full rebuilder gasket set for a early 350 that I did not use the whole set and it had the generic donuts without the steel inserts in them well, I put them on and they both blew out in a week. You have the right donuts with the inserts.

 

[udidwht]

Well after1,607 miles the passenger side donut let go again. Luckily I caught it before heading up the Grapevine. Stopped in armpit of Ca. and replaced it as well as the drivers side before continuing on.

I checked how tight they were before loosening and they were not 100 percent torqued. I'd heard the springs should not be compressed 100 percent. Is this true?

This time I torqued them down 100 percent then backed them off 1/8th a turn. Drove over the Grapevine and down to HB where im at now. I crawled under the following day and checked them and they appear in geat condition. I used a small mirror to allow me to see all around the joint. You can vusually see the donut with the flaired end of pipe mating it. Looks even all the way around with pipe sitting square.

I also retorqued them down 100 percent then backed them off 1/8th of turn. Used plenty of copper seize.

 

[udidwht]

With respect to the springs...do they go between the manifold and flange? Or between the flange and nut?

The flange that slides up the pipe over the (3) exhaust manifold studs.

 

[Nad_Yvalhosert]

I'd be looking at a partially plugged catalytic converter at this point. Too much back pressure and heat. Then the weakest point let's loose repeatedly.

Vehicle is in signature.

That may be so, but it's not available on my mobile device. So I'm gonna ask you to enlighten me anyway.