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So of the various straight fours I've owned, none came with a spring/tension mounted exhaust. All were fully cast/welded and one-piece. Yet all aftermarket upgrades are sprung. I have read that this is to prevent vibration cracking but have found no reliable information to substantiate this claim. Is there any reason besides ensuring easy installation and fitament?

I ask because I am considering a custom-fab mani (for a twin) and don't want to deal with springs and may use exhaust wrap. With a separate 2-2 system, fitament at the collector and both exhaust ports is a non issue, but if vibration cracking truly is an issue, I wanted to know before shelling out for something that is going to break. Any experts in this area?
 

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You're asking about the junction where the header mounts to the side of the cylinder? I have 2 aftermarket systems, both use the stock bolt-on mounts to attach header to cylinder. Not sure if I've seen many/ any systems where the header mounts to the cylinder with springs. Springs are used further down the system to connect collectors and can.

That junction- header to cylinder, is where any stress damage could occur because it's the most solid mount point, so I don't think vibration/ stress damage is a design concern- I think springs are used more for ease of installation/ removal.



Imagine this mess without the springs, using screw clamps instead!
4 into 2 into 1, then two more junctions up to the can. Total of 9 junctions.
That would be a lot of clamps to tighten/ loosen and line up to get it together.


 

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Chilehead
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The Zard on my 999R has springs all over the place, even to attach the pipes to the heads. It would be impossible to install if it wasn't separate sections, and even then it wasn't simple.

Tom
 

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In my experience, at least with car exhausts, if the exhaust is made of stainless, it tends to expand and contract a great deal, in the case of a car I had, it actually would extend and contract the overall length by 3/8's of and inch. Measured from the rear bracket, which had a rubber o-ring that would allow it to move back and forth. No shit, a full 3/8's of an inch. On bikes, I assume it is to let it float a bit, kind of isolating the exhaust parts from each other, allowing a bit of movement between them. I know from my old dirt bikes that solid mounted pipes would crack, I suppose from vibration, but those were old 2 strokes.
 

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Bingo ! We have a winner !

Springs are used where a flange would be impractical. Clamps are really not usefull because they only rely on the clamping force on the pipe.


You're asking about the junction where the header mounts to the side of the cylinder? I have 2 aftermarket systems, both use the stock bolt-on mounts to attach header to cylinder. Not sure if I've seen many/ any systems where the header mounts to the cylinder with springs. Springs are used further down the system to connect collectors and can.

That junction- header to cylinder, is where any stress damage could occur because it's the most solid mount point, so I don't think vibration/ stress damage is a design concern- I think springs are used more for ease of installation/ removal.



Imagine this mess without the springs, using screw clamps instead!
4 into 2 into 1, then two more junctions up to the can. Total of 9 junctions.
That would be a lot of clamps to tighten/ loosen and line up to get it together.


 
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