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  What's the cure for the cracking stock manifolds?

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What's the cure for the cracking stock manifolds? by mshill
Started on: 10-06-2003 04:10 PM
Replies: 9
Last post by: FieRoy on 10-07-2003 01:13 PM
mshill
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Report this Post10-06-2003 04:10 PM Click Here to See the Profile for mshillClick Here to Email mshillSend a Private Message to mshillDirect Link to This Post
Threee years and 15000 miles ago I did a complete rebuild of my car which included removing the obstructions in the manifolds and rewelding the flanges and cracks.

Now it has developed another crack just above the weld that fixed the last one. It seems these things were not made out of good material to begin with and that they will always crack no matter how/where they are welded.

Anyone have the ultimate cure before I go and stick my spare manifolds on?

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GT86
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Report this Post10-06-2003 04:40 PM Click Here to See the Profile for GT86Click Here to Email GT86Send a Private Message to GT86Direct Link to This Post
If it's the front manifold (closest to rear window), I would find a recall weatherstrip and install that. Keeps water and other crap from falling down onto a hot manifold. GM removed them as part of a recall, I guess the theory was to let more heat escape from the engine bay. However, water dripping down onto a manifold that's hot will eventually cause it to crack.

I see these weatherstips on ebay all the time, and PFF member Pondski usually has some as well (that's where I got mine). Easy to install.

Another problem could be missing/loose exhaust hanger springs. This could cause the exhaust system to vibrate excessively, which can also crack manifolds.

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jelly2m8
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Report this Post10-06-2003 08:06 PM Click Here to See the Profile for jelly2m8Click Here to Email jelly2m8Send a Private Message to jelly2m8Direct Link to This Post
Improper welding can cause them to crack next to the existing weld, you need to get good penetration with the weld.

Also have the manifolds bolted or clamped to a sturdy flat surface, they will warp if not, and can possable be stressed and cracked again after bolting them back up.
I use an old cylinder head to bolt them to when I weld the cracks and flanges.

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-=shame=-
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Report this Post10-06-2003 08:26 PM Click Here to See the Profile for -=shame=-Click Here to Email -=shame=-Send a Private Message to -=shame=-Direct Link to This Post
Good question, and good answers.
I believe that most of the guys around my work would ask why you didn't replace the manifold as opposed to repairing it. You saw that it was flawed/damaged and you were already rebuilding.
Has anyone thought of making a replacement for the weatherstrip out of a different material. Like a peice of aluminum to channel water/debris out of the way. Or just another splash sheild?
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Taijiguy
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Report this Post10-06-2003 09:36 PM Click Here to See the Profile for TaijiguyClick Here to Email TaijiguySend a Private Message to TaijiguyDirect Link to This Post
The water might be a valid assumption, but the spring hangers are the main problem. If you look at the entire system, the weight of the whole thing will pull on the manifolds if it's not suspended nice and tight. Make sure all the springs are in place, and tight. Replace them if they aren't. In the absence of the right springs, you can match up drum brake springs of the right length. Just remember they need to be tight.
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mshill
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Report this Post10-07-2003 01:32 AM Click Here to See the Profile for mshillClick Here to Email mshillSend a Private Message to mshillDirect Link to This Post
All interesting answers but I don't believe any apply in this case:

1) Its the rear manifold so weatherstrip is out.

2) The welds were done with a Tig welder and a welder wit 20 years experience did them.

3) The welds aren't failing it is the metal beyond the weld (on the collector tube).

4) All of the exhaust springs and hangers were replaced when the car was rebuilt.

What about ceramic coatings or exhaust wraps? Do other headers crack as well?

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RossT
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Report this Post10-07-2003 02:28 AM Click Here to See the Profile for RossTClick Here to visit RossT's HomePageClick Here to Email RossTSend a Private Message to RossTDirect Link to This Post
 
quote
Originally posted by -=shame=-:

Has anyone thought of making a replacement for the weatherstrip out of a different material. Like a peice of aluminum to channel water/debris out of the way. Or just another splash sheild?

There is a guy in florida that makes a "diverter kit" as a replacement for the recall weatherstrip. It doesn't look anything like the original, but it is much more effective. It's easy to install too.

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Carrolles
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Report this Post10-07-2003 08:05 AM Click Here to See the Profile for CarrollesClick Here to Email CarrollesSend a Private Message to CarrollesDirect Link to This Post
The crossover Y-pipe is rigid and is hard bolted to the outlet of both the front and rear exhaust manifolds. As the Y-pipe experiences thermal expansion it trys to force the exhhaust manifolds apart. This places stress on the exhaust manifolds especially between the outlet flange and the number 5 or number 6 cylinder branches. All of the exhaust manifold failures I've experienced demonstrate damage due to this stress. Surprisingly all of the failures I've experienced so far have been with the rear exhaust manifold.

A flexible Y-pipe would help aleviate this stress.

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mshill
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Report this Post10-07-2003 12:13 PM Click Here to See the Profile for mshillClick Here to Email mshillSend a Private Message to mshillDirect Link to This Post
The y-pipe expansion is likely to be the cause in my case as it has happened on the cyclinder closest to the y-pipe on the rear manifold.
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FieRoy
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Report this Post10-07-2003 01:13 PM Click Here to See the Profile for FieRoyClick Here to Email FieRoySend a Private Message to FieRoyDirect Link to This Post
Hello,

iīd like to respond on the stories about the crossover. The crossover isnīt the cause of the cracking. The exhaust is places very flexible to the car, so the expanding of the crossover isnīt the problem. The biggest problem is the expanding of the manifold itself. when it will get about 400°C, it expands about 0.7mm, between the cilinder on the left frontside of the car, and the middle one. (because the distance wetween those 2 is larger, then the other 2. The manifold has a bad design, but i have to say, they stay good for a lot of years though! I made a set of stainless ones, and they cracked in 1 month!

i canīt find a good solution for this problem. Only headers are! (iīm designing them right now. Have got a set of my own made of stainless steel, and they are perfect. Now designing new ones, with a little smaller diameter then mine (40mm pipe for each cilinder) and an easier design. (but every cilinder-pipe same length!)

Regards,

Roy
(i think, welding them never helps. the expanding has to go somewhere, where it canīt)

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