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Mk 3 - 850 ES Balance Pipes

Submitted by david_henshaw on Sat, 02/10/2010
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Commando

Commando Boffins:

Hi - my 850ES did not come to me fitted with the balance pipes that one sees in the parts book. Individual down-pipes and peashooters are fitted. I am fitting the Mikuni single-carb conversion as part of a serious rebuild and whilst this may have no bearing whatsoever on things, is it recommended that I fit balance pipes or not? What might the advantages be?

Peter the Commando Virgin

Submitted by david_evans on Sat, 02/10/2010

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I'm not sure that down pipes with a balance pipe are easily available. I also don't thing there is much value in having one. It makes removal and refitting of the system quite tedious and is one more part to collect dirt and go rusty and leak. As far as performance goes, I can't think of any performance bike that uses a balanced system. there may be some value in having a siamese system but that is a different kettle of fish. I rebuilt a BSA A65 some years ago and the two opposite sides of the balance pipe did not line up properly. They are still hanging on my garage wall with no place to go.

Submitted by steven_phelps on Sun, 03/10/2010

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i am wondering what makes this a "serious rebuild"?

personally i consider twin Amals superior, either fresh or resleeved.

the 850was supposed to develop more HP with the balanced exhaust.

many dontleave it, mainly because of fitting issues.

new copper exhaust gaskets are the best, tightened hot.

enjoy.

Submitted by iain_brown on Sun, 03/10/2010

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Due to the original cross over tube rigidly tieing the two pipes together there can be a problem with the exhaust fracturing in that area over time, which added to the difficulty of alignment and fitting is why 750 style are often fitted. My 850 is pre Mk III, i'm assuming the exhaust details are the same.

If there is a performance difference i'm not sure that it would be worth worrying about for road use.

Submitted by david_henshaw on Wed, 06/10/2010

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Dunstall put a crossover on his bikes that ran the stock camshaft and said that way they made the most power, almost as much as a bike with a race cam and open meggas except for on the very top rpm range.

I rode an 850 for years with the crossover pipes on it and it ran very well and had lots of mid-range. They did fracture a few times there, but I just grabbed a torch and an old coat hanger and welded them up right on the bike and went riding again.

Submitted by ashley_cutler on Fri, 26/11/2010

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Hi,

If you're fracturing pipes at the balance pipe area, then aligning and fitting and maybe quality of pipes needs looking at. Mine have not fractured in 15 years and have been on and off numerous times. They are fixed to each other and the head using the exhaust collets, so the whole assembly in this area should all move together as it is rigid.

As to whether they allow more power, I'm not sure and have used both Black Caps and Peashooters on my porky MKIII with little difference on performance, some earlier Commandos leave me when flat out, but this is at speeds which certainly mean loss of licence. If they eventually wear out, I'll replace them them with unbalanced pipes with a nice black zircotec coating.

 



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