I replaced both exhaust doughnuts 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 a flaky EGR can cause this? This RV has 454 YBI 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 (passenger side)
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 that 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 the other springs spun once tightened. I'm thinking the bolts did not tighten enough and air drawn in eroded away at the gasket. The drivers gasket side looks great after the return trip.
Vehicle is in signature.
If you've got super hot exhaust blasting away at those donuts because there's a gap and not properly fitted, yeah, they're not going to last very long.
yeah lean exhaust would do that. Any codes or bad mpg?
But also loose bolts.
Get Tap and run the holes clean before you replace with new bolts. The bolts should have flange where they are then sitting at the correct depth.
Those springs shouldn't move. When I changed mine - they treads where compressed almost all the way.
Well if you have a smog pump engine.... a bad gasket seal issue will be greatly magnified. GM set up the timing so late about 25 % of the combustion process is burned up in the exhaust manifold. After Burners with no bite is very descriptive.
Manifolds on this engine have the studs coming off the manifold (3 tri pattern). The flange slides down the pipe once nuts/springs are removed. OBD-1 no codes and only 1 single wire O2 sensor way down stream after the Y in pipes.
No AIR pump/s on this engine. No auto park brake either. Thank god...simplicity is bliss.
When replacing the nuts/springs with new ones I coated everything with lots of copper seize. Then tightened until the springs were roughly 1/16th or so from fully compressed.
the last time I replaced manifolds on my 350 they came with steel crush doughnuts
(https://external-content.duckduckgo.com/iu/?u=https%3A%2F%2Fi.ebayimg.com%2F00%2Fs%2FMTI0MFgxNjAw%2Fz%2Fgo4AAOSwav5ap7L5%2F%24_57.JPG&f=1&nofb=1)
not that ceramic gasket stuff anymore. seems to be holding up nicely.
Maybe you got a bad set of doughnuts not designed for the hot running 454?
Now that you mention it, I replaced mine with steel crush as well.
Update:
Everything holding well after a run over to Pothole reservoir from Seattle area and back. When I did them in Ca. I was unable to get new/nuts only the donuts. After getting back home crawled underneath and the springs could be wiggled and spun by hand (not cutting it.) I replaced all the nuts/springs with new ones. Used lots of copper seize. Also wrapped my trans lines and oil lines with 2000F heat wrap where they run near manifolds.
Excellent! Thanks for the update.
:)clap
Well...
I hit the road (Renton, Wa.- HB,Ca. and just before hitting the Grapevine I heard the exhaust donut. Pulled off in the armpit of Ca. Bakersfield and sure enough after 1.670 miles the passenger side donut was toast. When I replaced them previously I had bought new springs and nuts. Installed (2) donuts on each side and on the road again.
On the way home I again had the donut leak again but this time on the drivers side (Bad words here) lol! This was in Chiloquin, Or. I had exactly 1,072 miles on them. When I pulled the pipe down the passenger-side was beautiful but the drivers side had about a third section of the wire exposed. So I installed (2) new donuts and on the road again. Prior to installing I checked the pipe ends and no signs of carbon, grease etc. Wire brushed them and wiped them clean prior to installing the new donuts.
I do remember when I installed the donuts in Bakersfield that they fit loose. I needed a small amount of copper RTV to hold them up on the manifold. They did have the steel liner.
Take a look at the how to video below. Notice one glaring oversight. He has totally missed the seat where the exhaust donut fits into. It's a rusted out dirty sealing area. Yes you have to clean up the header seating area or exhaust gases will blow right thru the seal. Then there are those with sleeves...does your engine have new exhaust doughnut sleeves?
https://youtu.be/meMQnOVTPqU
https://www.rockauto.com/en/catalog/chevrolet,1994,p30,7.4l+v8,1059634,exhaust+&+emission,pipe+flange+gasket+/+seal,5836
This link may contain the part, the p30 is listed
https://www.gmpartsdirect.com/oem-parts/gm-multi-purpose-seal-15592451?c=az0x
1. Pipe ends were clean, clean prior to install of the gasket.
2. Manifold was clean and flat.
3. Gaskets included steel insert
4. FEL-PRO # 60584
What I did notice was the gaskets I had in my toolbox (60584) fit into the manifold in slightly loose (insert side). Requiring me to add a small dab of copper RTV on the steel insert to aid in holding up the gasket. When I had drop the pipe again in Chiloquin, Or. I had a couple extra of the same gaskets (new) and they fit tighter. Tight enough that it required me to tap them into place till flat against manifold. Odd given they were the exact same part number gaskets. Even had the old packaging to compare. It would be nice if someone put out steel/or copper solid gaskets donuts for the 454 of this year. Can't find any anywhere.
Here's a couple of pics of the bad gasket removed in Chiloquin, Or... You can see the side it burned thru was the manifold side not the pipe side. What I suspect was due to the loose fit the exhaust gas managed to get in between the manifold and steel liner. But why only the drivers side? Both gaskets were loose fit (steel insert side) at install.
It would seem opportunity knocks! Do not over think this
I assume you have a spring loaded setup, if so it might very well be time to replace that setup. It is quite apparent sealing the exhaust gas containment is not taking place. Late timing in my opinion would be the fundamental cause. Turning exhaust manifolds into after burner containment has a price. Little tounge in cheek going on..but think deeply about it, take a heat gun some time and measure the temps. It is stunning.
.
By chance are you connecting the entire run of exhaust to the exhaust manifolds? It can be difficult to get things seated properly with that much weight and a possible misalignment.
No, the hangers down wind are in good shape. Pipes are as best I can tell-see nice and lined up. I've racked 500 miles since replacement and crawled under and they look good (used small mirror). I did buy (2) Mahle donuts in the event that...(you know the rest lol).
Upon checking springs have no play.