Norton exhaust

JD

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Jun 1, 2007
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Hello all-
I would love your thoughts on the exhaust for my Mk3... I have restored another to nearly stock with very mild mods, as seen in my posted pic earlier. This other Mk3 I am doing, I thought about eliminating the balance pipe and running straight exhaust headers with the pea shooters. I have had fitment problems with the Mk3 exhaust with leaks around the balance pipe. after trying a couple of different combinations of pipe styles, I was still left with slight leaks at the exhaust nuts and in the balance pipes, themselves. The bike currently has pea shooters and a balance pipe, but the pipes have been cleverly cut and rewelded to eliminate the problems myself and others Im sure have encountered. I hate to break tradition, as my restos adhere mostly to stock running conditions, but I would love this bike to snort and scream away from stop lights. Thanks again.
JD
 
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Have you tried instant gasket on the exhaust joints? It's the best place for it.

Cash
 

Ron L

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JD,

The best way to get a balanced system to fit is to find and original one and clean and re-chrome it. I have found fitting balanced systems is one of the most frustrating jobs on a Commando. I tried to mount a balanced set for a low muffler Interstate, and after two sets from two different suppliers, the closest I could get the crossover alignment was half the diameter of the mating stub!

Your Mk3 should use the belled end pipes, which I find slightly easier to align properly and maintain seal. I have installed a non-balanced version of these on my Mk3 cafe racer and have used them on other non-Mk3 models as well.

The nonbalanced systems are easier to fit and maintain, but I can't say I have seen a noticeable difference in performance.
 

L.A.B.

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Ron L said:
The best way to get a balanced system to fit is to find and original one and clean and re-chrome it.

The 'TOGA' (UK made) Mk3 balance pipe system that I bought to replace a set of unbalanced pipes (one of them had cracked at the belled end) fitted perfectly.
 
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Okay, all. Tell me this: when I bought my '70 Commando Roadster some 20 years ago, the [original [?] owner included a set of Paul Dunstal [ANTI] silencers and a 2nd set of head pipes with a flexable cross-over. So, has anybody seen / heard of such a setup?
I know the bike was purchased new at Gus Kuhn[?] Motors in London, used to tour Europe [as it also came with a Craven luggage rack] and shipped to the USofA in 1970.
I suspect the accessories are period but I don't know if either is significant. Opinions?
 

Ron L

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Yep, Dunstall supplied a crossover exhaust for Norton before the factory. By using the flexible connector, he avoided the stress and alignment problems of the factory system.

As far as I know, no one has made this system or a similar one since the early seventies.
 
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Exhaust Gas Scavanging

I understand the theory of cross-overs is to even out the exhaust pulses and thereby reduce intake backpressure and promote a more efficient fuel charge and burn. Right? And, smaller diameter exhaust pipes promote faster gas flow, hence better scavanging. So I wonder, which should benefit Ed [with 932 Amals] most...1 1/2 inch ID pipe and muffler system sans crossover [at CommandoSpecialties] or retaining 1 3/8 inch Dunstal pipes with the cross-over?
 

Ron L

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932 Amals on a '70? Have the ports been matched? Or at least use the '74 style 32 to 30mm manifolds? You will still have a mis-match (750 head intake measures 28.5mm).

Anyway, if the intake situation is taken care of, you would find better street performance with the 1 3/8 crossover exhaust than the 1 1/2 noncrosssover. That said, the best peak horsepower may be made with the bigger pipe. This is all probably splitting hairs for a streetbike. My $.02.
 
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