exhaust mountings, solid or rubber mounted, thoughts ?

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holty
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Sat Aug 10, 2019 3:39 pm

my rotax 290 keeps splitting the downpipe , the pipe has 3 rubber mountings and is clamped to the stub, end can is on a rubber bobbin as well, would a solid mounting be better ? your thoughts please

Ken Tucky
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Sat Aug 10, 2019 4:57 pm

Couldn't you spring mount it at the stub end, then you would have a fully floating exhaust?
You may have already tried this?
Any flexing/movement will always transfer to the bit that's fixed = cracking.....
Maybe worth a try...........

Mr Tucky

Warkton Tornado No.1
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Sat Aug 10, 2019 5:44 pm

Flexible mounts allow the exhaust to function properly as well as avoid splitting through vibration. Have a look @ Kart Forums & you can appreciate the lengths they go to in avoiding anything like rigid mounting, even using flexible headers in some instances.

That said, the material utilised in the construction is important. Blown exhausts tend to be very resilient in my experience. Perhaps it may pay with any repairs (presumably steel) to use brazing rods which requires less heating to work. Often steel welded up becomes hard through carbonisation (I think!) :?

holty
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Sat Aug 10, 2019 6:16 pm

I quite like the idea of a flexible joint, I presume its like cars have, a sort of braided steel, when I repair it it just seems to crack somewhere else, it is all on rubber mounts at the moment, I guess its the resonance that vibrates back and forth that splits it.

a.lo.v2
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Sun Aug 11, 2019 12:01 pm

my thought is you must have all solid mounting or all flexible mounts and not a mix of either. used to have a Mickek that bobbins on the body and solid downpipe......always was going to crack and did.

Ken Tucky
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Tue Aug 13, 2019 4:58 pm

100% agree with a.lo.v2.
What you seem to have is 3 flexible points and one fixed, ''the pipe has 3 rubber mountings and is clamped to the stub''
If you let it 'float' at the stub your problems may disappear.
If its any help, my sprinter has 2 bobbins, one is situated about mid point at the biggest diameter section, one on the cone near the end just before the end can and is spring mounted to a TS1 type stub. I seal it at the header end with silicone sealant.
Works for me, and this pipe and brackets has not cracked at all.
Mr Tucky

holty
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Tue Aug 13, 2019 5:35 pm

Ken Tucky wrote:
Tue Aug 13, 2019 4:58 pm
100% agree with a.lo.v2.
What you seem to have is 3 flexible points and one fixed, ''the pipe has 3 rubber mountings and is clamped to the stub''
If you let it 'float' at the stub your problems may disappear.
If its any help, my sprinter has 2 bobbins, one is situated about mid point at the biggest diameter section, one on the cone near the end just before the end can and is spring mounted to a TS1 type stub. I seal it at the header end with silicone sealant.
Works for me, and this pipe and brackets has not cracked at all.
Mr Tucky
thanks for your reply, i have taken the clamp off the front and gone back to springs as you suggest , my mounts are about the same as yours, so will give it a try and see if it lasts longer.

Ken Tucky
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Wed Aug 14, 2019 5:13 pm

Hope it works for you Holty
Mr Tucky

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garry inglis
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Wed Aug 14, 2019 6:32 pm

hes forgot to mention the 42hp is not helping lololol

Ken Tucky
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Thu Aug 15, 2019 5:42 pm

Its holding it down, not holding the exhaust that's the problem eh!
43 hp on the road.....................interesting.....................lol
Mr Tucky

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