Exhaust donut burned again? (1 Viewer)

CruiserTrash

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I’ve replaced the gasket/donut between the manifold and downpipe four times in the past year, and every time I open up that flange the donut is burned up. The one picture below was in for three weeks. This one was a Japanese made Felpro.

Stock 2Fmotor with a Jim C carb. Compression ranges between 129-140. Temperature sender was replaced 5 months ago and the gauge holds steady around 2/3 all the time.

What’s the deal? Normal/known issue? Top end getting hot but not registering at the sender correctly? Valves? I’m at a loss.

460DF144-E0A3-4935-9087-B2106412E43A.jpeg
 

g-man

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Doubtful you can "burn up" a donut gasket. But the typically do unravel like this when you take them out. They are a one time and done thing. If you are having an exhaust leak at the gasket...the reason for taking them out, then I'd suspect a warped flange on the exhaust pipe. If it's apart check the flatness between the stud holes. You may need to double up two gaskets to seal the gap. You can also replace the flange, have a new one welded on.
 

CruiserTrash

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@g-man The gasket material (between the metal) is ash. Burnt to a crisp. If you blow on it, it flies away like cinders. 😬
I’ll check the flatness today - I have it apart anyway. Thanks!
 

g-man

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Lots of carbon can build up on the gasket and the adhesive between the metal bands maybe gets burned up to ash but the metal bands should hold, at least until you start handling it. I've never pulled a donut gasket because it was "burned". Only because it leaked. IT"S doubtful that it burned up to the point it leaked. they are built to handle LOTS of heat.
 

CruiserTrash

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@g-man So it’s purely the metal bands doing the sealing then? In the photo below the green fiber stuff is what’s turned to ash. I have this apart to do my manifold gasket - I did put a new one in three weeks ago because it was leaking, even though I knew I’d be taking it all apart this weekend. Easy three-bolt “job” that took 15 minutes.

FE12BEE1-31A1-4C95-877F-7D67AAC4B81C.jpeg
 

g-man

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Everyone I've ever taken out that's had some time in there had crumbled. You'll need to take the entire down pipe off to measure the flatness. IT's a pita cause you have to take it loose at the cat and at the smog hose and the hanger/bushings. If you try and bend the crap out of it pulling it down, you'll end up with a leak at the other end near the cat. Probably your easiest solution is to just slip two gaskets in there and hope it holds. Second thing and probably a stronger solution is to get the flange (check ebay) and take it to a muffler shop with another gasket.
 

CruiserTrash

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Long ago somebody removed the flange at the cat .... this would probably be a “drop it off with my exhaust shop” deal. They DID just replaced the bad exhaust check valve for the smog gear so at least that will off off easily. Couldn’t source a Toyota one - or anything with the same threads - so they welded SAE threads to the end of the pipe. Those check valves are readily available.
 

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