Interstate 850 Mk2: No balance pipe

Hi All:
Some more advice pls....
The Commando I have bought (I believe Mk2) has not got a balance pipe, and the exhaust downpipes fitted clearly have no provision for adding a balancer. They terminate in peashooter exhausts which look correct.
The machine is fitted with KM/H speedo (I suspect originally) and I would like to know if there were any Commando 850 models fitted without balance pipes or was this another PO 'modification'



Thanks for your help Guys, this really is getting to be a voyage of discovery.

Hi Marknorton

I brought my 1974 Norton M11 new and they came from the factory with balance pipe, but my opion is they run better without the balance pipe, as for the speedo mine came with a MPH speedo, mine was brought in Brisbane Australia new, so I don't know if they had KM speedo when sent to other countries, when I convered my Norton to a 1957 Wideline Featherbed frame in 1980 I got a set of header pipes made up without the balance pipe and I'm still running with the same headers now...

Hope this helps

Ashley

PS You look like you have your work cut out for yourself with your bike, have fun...

Its been said the only reason the zorsts got a balance pipe was to try and cut the noise down for decibel testing - feeding into two mufflers loses a decibel or 2.

Keeping the balance pipe system free of exhaust leaks was a near constant battle, and it also caused a lot of exhaust pipe fractures, just around the junction of the balance pipe addition. And also stripping of the exhaust nuts into the cylinder head port. So you are far better off without the balance pipe...

P.S. They also altered 2nd gear ratio to a slightly taller gear for the same noise reasons - the noise testing was done flat strap in 2nd gear, so raising the ratio slightly reduced the acceleration slightly, and passed the noise test. Oiling the chain before the test also helped...

The 850 Mk1 I bought in 1977 still had the original peashooter mufflers - they were straight through, with the little flutes in the inside walls. And the little circular "mutes" in the end of the mufflers that were removable - town and country style. With the mutes in, the exhaust was surprisingly quiet (so thats what all those decibels was about) and with the mutes removed, the exhaust was quite rorty. Mutes are shown in the parts list. Jets in the carb needed altering to suit the mutes though, so it wasn't a 10 second job...

Cheers.

marknorton said:

The Commando I have bought (I believe Mk2) has not got a balance pipe, and the exhaust downpipes fitted clearly have no provision for adding a balancer. They terminate in peashooter exhausts which look correct.

Click to expand...

All 850 models were supposed to have had the balanced exhaust system. Your Commando appears to be a Mk2A model, as it has the black plastic airbox-so it should have had the annular discharge "black cap" or "bean can" silencers originally, and not peashooters.

That is very interesting LAB, as the exhausts are definitely pea shooter type. I think the PO must have changed the entire exhaust system.... SO that is something else on the list not budgetted for !!

There's no reason to change the peashooters, unless you intend to do a 100% original restoration job?

Just make sure your main jets have been increased, I went from 230 to 260 as the peashooters are freeer flowing. Keep the peashooter, the blackcaps are boring.

No LAB will be a total restoration. An thinking of setting up a restoration thread. the peashooters are:



As you can see reuse is not really an option

A balanced pipe increases power; Dunstall discovered that quite early with the Commando and published that information in his tuning guide. It appears to me that Norton then "copied" his design (though without the flexibility that the Dunstall parts had) and incorporated it into the 850. It also reduces noise so it's the best of both worlds. The problem is that on the Commando, as noted, it is difficult to keep it from leaking/cracking because Norton (unlike Dunstall) used "hard" parts. So it seems that most 850s were eventually just changed to the 750 exhaust. I looked into getting the balance pipe setup back onto my 850 but it is difficult to find the parts. When I checked a few years ago, I believe Viking was making them (though I could be remembering that wrong) but they were quite expensive. So I just stayed with the 750 exhaust.

Page 22 of the Dunstall tuning manual shows the 750 balanced system which looks exactly like what Norton did to the 850 later.
Dunstall states: "By far the best system for fast road work is a separate exhaust joined by a balance pipe up close to the cylinders."

I got a pair of balanced pipes on E-Bay to use on my '72 Combat with Dunstall mufflers. If the balance-pipe clamps are kept loose the front exhaust-pipe configuration is very rigid and stable--the pipe-to-muffler clamps also allow a little "dancing" to compensate.

I'd say decibels are down a fair bit and deeper in register, like an 850--horsepower and mpg are up a couple of clicks. This has proved the most efficient setup of all on the Combat aside from SS-type pipes with Dunstalls plumbed to terminate past the rear wheel. The Combat has 220 main jets in 932's with the needles in the lowest position--with my antique black-leather saddlebags thrown over the fender it's a very practical daily rider.


Tim Kraakevik
kraakevik@voyager.net
Three Commandos