Donuts, anyone? Seals, I mean...

[Nomadicflyer]

Question: I have a donut exhaust seal that keeps blowing out on me. I thought the nuts were backing out, because they would be missing, so I put in some bolts with safety wire. The bolts stayed put, but the exhaust seal still blew out. Several times. Is there any other reason for that to happen beyond an alignment issue between the headers and the Y pipe? My next step was to cut off the flange and put a new one on, with a fresh alignment.

1972 C20 350

Thanks!

[kwmech]

There should be a steel sleeve inside of it. Sounds like you have just the donut sitting on the bevel of the head pipe

[Stocker]

Originally Posted by kwmech

There should be a steel sleeve inside of it. Sounds like you have just the donut sitting on the bevel of the head pipe

Originally Posted by Nomadicflyer

KW Mech~ There's no shoulder on the seal, is that what you mean? I think the inside is just the same malleable band that wraps to make the seal.

I don't have a pic, but many years ago I had mine apart and there was a short (2"-3"?) section of pipe that fit snugly inside the donut. The pipe slipped up into the exhaust manifold and down into the exhaust pipe, and it held the donut in place so it couldn't move or blow out.

[B. W.]

I'm not sure we're on the same page. Do you have stock exhaust manifolds or headers? There's a big difference in the gaskets. If you have stock manifolds go with what everyone else said & ignore my post!

[kwmech]

Originally Posted by Stocker

I don't have a pic, but many years ago I had mine apart and there was a short (2"-3"?) section of pipe that fit snugly inside the donut. The pipe slipped up into the exhaust manifold and down into the exhaust pipe, and it held the donut in place so it couldn't move or blow out.

That's what I'm referring to

[B. W.]

Do you have the flat, three hole flange? If so, the best option (in my opinion) is to replace it with a ball flange or a "V" clamp flange depending on if you need it to flex a little or be rigid.

[67 chevelle]

Originally Posted by B. W.

Do you have the flat, three hole flange? If so, the best option (in my opinion) is to replace it with a ball flange or a "V" clamp flange depending on if you need it to flex a little or be rigid.

Excellent advise ,, ball flange is the way to go

[demian5]

I had an issue with using crappy bolts that would stretch when they got hot. Replaced with Grade 8 and no longer an issue.

Also what kwmech said. Is it a floater?

[El Dorado Jim]

http://www.autozone.com/emission-con...159144_79733_0 these are sintered metal donut gaskets,you can also get them thru Summit....or Amazon....I had the same problem as you,now I only use these,they don't deteriorate like the other ones...part #60985 Felpro..will fit your 350

[Nomadicflyer]

Thanks, Jim~ I'll try those. They look like what I've been using, but it's been a while, so I'm not sure.

Demian~ Yeah, I wondered about that. I switched to Grade 8, hoping it would be an easy fix. As is normally the case, it couldn't be simple.

KW Mech~ There's no shoulder on the seal, is that what you mean? I think the inside is just the same malleable band that wraps to make the seal. I'll pay closer attention, this time. This time I've caught it before it disappeared on me, I'll pull it out and see what's in there.

B.W.~ I have the 3 hole flange. I'm not sure what would happen with a ball socket/v band type clamp. Have you used this? Does something else crack, is what I would be concerned with.... I don't know?

Thanks, all. I'm done painting for the day, now I'll tear into the engine and pull stuff apart.

[Nomadicflyer]

Stoker: Thanks for the reply. I remember having a rig that was like that, with a slip joint section inside. This one doesn't have that, maybe I need to find one?

BW: I'm dealing with stock exhaust manifolds and dual exhaust, each side runs straight back. Sorry for the confusion.

KW: I understand better, now. I'll be looking for an option like that one, I remember that works pretty well.

We pulled the exhaust apart, last night. The right side donut was coming apart, and after closer inspection found the alignment off by about 1/2 to 3/4 inch. I think when I changed the engine mounts, the engine position changed and it put a strain on the pipe. I started eating seals. I noticed there is no give at all in the exhaust, from the manifold back. I wonder if cutting the 4 metal strap hangars and putting in rubber hangars would help, or if I should put in some form of flexible flange at the manifold connection? Both?

The more I think of it, the more I think there should be some mechanism that allows for some flex in the exhaust? Even if I put a perfect coupling to the manifold, isn't there an issue without some form of give to the system? This thing is solid, doesn't even wiggle. Put it in 15 years ago, and I think I was focused on making sure it had ample support, being a larger diameter pipe and dual Thorley mufflers.

Thanks all for your input! The farther along the path I get, the more I reach out for opinions from others. Something about the gray hair, I guess.

[Nomadicflyer]

Argh. New problem.

[B. W.]

I've run them cracked for many years. The best option is to replace them. I have welded them in the past. I was pre-heating this one before welding. Your cracks are not severe, I've seen them worse.

[Nomadicflyer]

Points to KW Mech. I pulled apart the other side, and it has the sleeve/reducer that KW had mentioned. Apparently, that evaporated during the engine mount change and I've been burning through exhaust seals since.

Of course, they weren't even in the book at NAPA. I found a reducer that wasn't quite right, but close enough to open up/trim down and install. Hoping this was my smoking gun for the seal issue. Pics to follow.

B.W., I wondered if the cracks had been there for a long time. I went ahead and got an exhaust manifold coming. 125 bux for the Dorman one.
(https://www.napaonline.com/en/p/NDP6002387)
I'll keep the old one as an emergency spare. I've seen all kinds of cracking issues with welding cast iron. Good on you for getting it to take!

Thanks for all the help!

[B. W.]

I'm glad you got it figured out, I'm running new dorman manifolds too. Not worth wasting the time to weld them & you're right welding is hit & miss!