Exhaust mounting theory

[Easy-X]

It's a bit of a tough one to Google search as the question gets drowned out by tuning questions. What are the do's and don'ts and principles of mounting an exhaust system on a bike?

For example, on my Husky you start with the engine exhaust outlet and the down pipe is two studs and a crush gasket i.e. pretty solidly mounted. The down pipe is solidly clamped to what 390/401 owners refer to as the "bread box" - a large sound-shaping chamber - which is rubber-mounted to the frame. This box has a short link pipe clamped to it then the end can is held on with springs to the link pipe and a rubber hoop mount to the frame. tl;dr flexible mounts everywhere but at the engine studs.

Now with the GT there's the same stud mount at the engine but the down pipe is also bolted to the frame at the other end. The equivalent to the end can is clamped to the down pipe and also bolted to the frame. tl;dr zero flexibility anywhere in the system.

I recall a conversation with a friend who restores old motorbikes where I suggested a rubber mount for the end of the exhaust and he said no as you wouldn't want to introduce any stress at the exhaust studs end. But now I'm thinking: hang on, these are old (or old design) bikes with steel frames, surely they flex anyway

And before anyone says: "they spent a lot of time and money researching this stuff, leave it alone!" This is Royal Enfield we're talking about
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Royal Enfield Continental GT 535, Husqvarna Vitpilen 401, Yamaha XSR700, Honda Rebel, Yamaha DT175, Suzuki SV650 (loan) Fazer 600, Keeway Superlight 125, 50cc turd scooter

[stinkwheel]

Well, the older bullets have the header as a push-fit in the head, the exhaust manifold is a tapered hole and you just give the header a whack into there with a mallet to seat it. It has a bracket from the header attaching it rigidly to the main engine bolt at the front of the frame. The silencer is then attached rigidly to the frame in two places.

They made them like that for 75 years and I've never heard of anyone having issues with it. None of the engine mounts are elastic, it's all rigidly attached to the frame. The engine has no business moving about. In fact, ut was one of the first bikes to use the engine as a fully stressed frame member, if you drop the engine out, the freme springs apart and is hell of a bendy (I wouldn't dare sit on one with the engine out, you'd damage it).

I'd imagine a lot of more modern bikes have elastic engine mounts, if the engine can move, I'd expact you'd need to introduce some flexability in the exhaust system.

I'm not sure how they attached the engine on the 535, it's a full cradle duplex frame so presumably the engine's not a stressed member in the same way.

Are you having issues?
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“Rule one: Always stick around for one more drink. That's when things happen. That's when you find out everything you want to know.”
I did the 2010 Round Britain Rally on my 350 Bullet. 89 landmarks, 3 months, 9,500 miles.

[Easy-X]

No issues as such, just trying to understand what seem like wildly different setups. I am thinking of removing the redundant pillion pegs and the RH one also has the exhaust bracket so I'll need to at least fish around for replacement fixings. Just curious if a rubber mount there would be help or hinderance.

FYI the GT engine is held within the frame through engine plates:

https://accessories.hitchcocksmotorcycles.com/32682
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Royal Enfield Continental GT 535, Husqvarna Vitpilen 401, Yamaha XSR700, Honda Rebel, Yamaha DT175, Suzuki SV650 (loan) Fazer 600, Keeway Superlight 125, 50cc turd scooter

[that_impulse_guy]

if its 2 stroke, then the engine tends to be rubber mounted and so is all contact points of the exhaust, except where it screws directly onto the barrel with whatever bolts/studs/springs they felt like using. The entire thing can wobble on a microscopic basis.

my 4 strokes have the exhausts hardmounted.
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Gone: Yamaha DT50lc, Suzuki DR500, Suzuki A100, Kawasaki z250ltd, RD350YPVS, Suzuki DR Big, Kawasaki AR125, Kawasaki KMX200, Suzuki GS1000S, Katana 1100, GS550M, Suzuki RGV250
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