Norton exhaust

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Jun 1, 2007
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.
Have you tried instant gasket on the exhaust joints? It's the best place for it.


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.
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.
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?
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.
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?
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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