Need help with exhaust

Hi all, I'm a new Norton owner and have a question about my 1975 850 Commando exhaust. I need to replace the right side pipe because it has a pretty good dent in it, but I believe that it is an aftermarket system. My biggest question is I'm sure the mufflers are aftermarket, but I'm not sure if the pipes are? They have a cross over built into the top of them and I can't seem to find a replacement. So I guess I need to know what kind of system is on my bike and where I could find a replacement like it. If it will be tough to find a replacement could I just buy a new pair of pipes without the crossover and would they be a direct replacement. Any help would be greatly appreciated. Thanks!

Here are a couple of pictures:

Hi Kustomiser, welcome to the Norton nuthouse. You have what appears to be an original 850 Mk3 factory header pipe system, with what appears to be Dunstall Decibel mufflers. The original mufflers were technicall designated Annular Discharge known as Black Caps or "bean cans". Heavy and restrictive. However, if you don't want complete authenticity for your bike, by all means keep the Dunstall mufflers. They are efficient and sound absolutely glorious. The original crossover header pipe system can easily be replaced by after market 850 seperate pipes. These are commonly available. The cross over set up is a bit of pain to fit whereas the seperate pipes are straight on and easy to adjust into alignment with the mufflers.

Mick

Mick, thanks for all the info, that was exactly what I was looking for.

Jim

Keep in mind that the head end of the pipes are different on a Mk3. When replacing the pipes, you can use the earlier 850 pipes, but you will need to remove the beveled seat from inside the head exhaust port and use the standard Norton gasket. You will also need to use the exhaust rose ("nut") collets from the '73-'74 850 or use 750 exhaust rose (no collets) if you are using 750 style non-balanced pipes.

The Mk3 pipes have a belled end to allow some movement for alignment. Earlier 850 and 750 pipes have a flat flange. Finding suitable replacement balanced pipes is an exasperating exercise. Few aftermarket balanced pipes will align properly and will crack at the balance pipe.

If you were closer you could have my old ones since I'm not a fan of the look of a balance pipe.

OK, I need to know what the difference is between a 850 Commando and an 850 MK3 Commando and how do I know what I have or are all 1975 850 Commandos MK3's?

Coco said:

If you were closer you could have my old ones since I'm not a fan of the look of a balance pipe.

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How much? Would they be a pain to box and ship? Let me know what you think.

kustomizer said:

OK, I need to know what the difference is between a 850 Commando and an 850 MK3 Commando and how do I know what I have or are all 1975 850 Commandos MK3's?

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What they are saying, if I understand is that MkIII PIPES are different, but the head, etc. are more or less the same.

kustomizer said:

OK, I need to know what the difference is between a 850 Commando and an 850 MK3 Commando and how do I know what I have or are all 1975 850 Commandos MK3's?

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The easiest way to answer that question would be to remove the R/H pipe and find out what you've got.



If it's the standard 850 MkIII setup, then you should find a pipe with a flared end,-like this?:



Also, a loose conical seating ring between the pipe and head, and two semi-circular collets with a profile matching the pipe in between the pipe and the inner end of the exhaust nut?

I'll pull them off this weekend to see what I have, thanks.

kustomizer said:

OK, I need to know what the difference is between a 850 Commando and an 850 MK3 Commando and how do I know what I have or are all 1975 850 Commandos MK3's?

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The MkIII Commando came out in '75, and is easily distinguished from earlier bikes by the left-foot shift and rear disk brake, and were available with electric start. There are a bunch of other changes, too.

There are a fair amount of Commandos out there that are titled as '75s, but are not MkIIIs, likely leftover '74s that were first sold in '75.

MkIII pipes will fit on an earlier bike and visa versa, but you need the pipes, the exhaust nuts, the gaskets and collets to all be the same.

Like Ron said, if balanced pipes aren't properly aligned, they'll crack at the 'y' of the crossover. I cracked 2 and switched to 750 (unbalanced) pipes.


Unbalanced pipes are a little louder, as each exhaust only goes through one muffler instead of two.

Great info, thanks. Based on that description mine must be a MKIII, thanks again for the info!