Converting 850 MKIII exaust to Pea Shooter type. How? (2006)

My MkIII has an original set of Paul Dunstall silencers on it and I am partial to the Pea Shooter type. I want to move up to larger bore 1 1/2" pipes on there and I could use the Dunstall silencers, but I am not really into how they look.

I realize the MKIII uses a different exaust nut and some kind of sherical mount or bushing in there and I wondering exactly what I need to do to make the conversion.

I know the Dunsatlls are the original engraved version and some think they are a desireable piece but I don't like their appearance as they seem to be a bit longer than the older Pea Shooter silencers. Are they something I could sell and get a decent amount of cash for them to put towards a new system or should I just hang on to them?

I am assuming I have to buy a while new system with mounts. Will getting rid of the balance tube affect anything with performance?

I personally agree with you about the looks of the Peashooters over the Dunstalls. I like the way they look, and sound, better, myself. Performance be damned! (We're going to hear arguments about this!)

I would buy a whole new system if I were you. The cardinal rule of owning a classic, or special interest machine is: Never part with any of the original equipment. Or, anything that came with the bike that fits it. Not only will it increase resale value, if that sad day ever comes, but if, like most of us, you acquire another Commando, you may need to use some of those parts.

As far as the balance pipe effecting performance goes, that's a good question. Has anyone got any facts, or educated opinions on this subject? I have heard arguments both ways.

Hey Coco-
You can look for peashooter mufflers listed for Triumph. They have a more universal mount on them and would make life a lot easier. I believe you could keep your pipes this way and since reverse-cones arent original anyway you haven't lost out on that aspect. I do agree, though--Peashooters look right on a Commando!
I changed from stock crossover (73 850) to 750 type non-crossover pipes and didn't notice much difference by "seat of the pants" performance-wise. I did notice a big difference in the exhaust note, though. Went from nice and (overly) mellow to a great snarl!

Mike
Kansas, America

Thanks for the tips guys. The Dunstalls on there now have that Triumph type of a slide mount. I realize I will have to get new brackets if going to the Peahooter type and I do want the large bore exaust. Not sure if 1 1/2" or 1 5/8" is the way to go. How about brands? Any exaust brand better than others? I would love to stay away from Chinese/Taiwanese stuff and stick to british or USA made as the quality will be better. I have heard the name Toga before and wonder if they make a decent system. I am in fact looking for that nice snarl in the sound so the extra volume won't be a bother, it will be welcomed.

To those who have done the conversion on an MKIII 850, what about those sherical mounts and exaust nuts? The exaust nuts on the 850 look shorter than the older 750 type, and how do I work around that? Do I buy the shorter 750 type once the older exaust system is put on?

Coco said:

The Dunstalls on there now have that Triumph type of a slide mount. I realize I will have to get new brackets if going to the Peahooter type and I do want the large bore exaust.

Click to expand...

If you buy a complete 1.1/2" system then I would expect it can be ordered with any necessary brackets.

Not sure if 1 1/2" or 1 5/8" is the way to go.

Click to expand...

I know 1.1/2" systems are available, I'm not sure how easy it is to get 1.5/8" though (I'm not sure there is any benefit in using 1.5/8" pipes anyway?)

How about brands? Any exaust brand better than others? I would love to stay away from Chinese/Taiwanese stuff and stick to british or USA made as the quality will be better. I have heard the name Toga before and wonder if they make a decent system.

Click to expand...

Yes Toga is good quality, although I'm not sure if they do a 1.1/2" system or not?

To those who have done the conversion on an MKIII 850, what about those sherical mounts and exaust nuts?

Click to expand...

It is possible to get *Unbalanced* pipes to fit the MkIII seatings so there may be no reason to change the head fittings at all (I know they exist because I have a pair).

The exaust nuts on the 850 look shorter than the older 750 type, and how do I work around that? Do I buy the shorter 750 type once the older exaust system is put on?

Click to expand...

I don't think you need to change the exhaust nuts in order to fit the earlier flanged pipes (even the earlier balanced systems on 850 MkI/II had flanged pipes with the same nuts used on MkIII), what you need to change are the internal parts, the MkIII seating and retaining collets need to be changed for the earlier 850 MkI/II 063990 retaining collets (those collets do not appear to be used with the 'long' nuts used on 750s) and 063995 sealing washers.

I know RGM Motors http://www.rgmmotors.co.uk/ sells a selection of big bore 2:1 and 2:2 (including chrome/black chrome peashooter) systems although their web catalogue does not really show many good photos unfortunately!
Here is one at least of their RGM 2:1 short megga = http://www.rgmmotors.co.uk/images/full/full_471a.jpg

I think they will send you some better photos if you ask?

Don't bother with 1-1/2" pipes, they don't buy you anything. Get a pair of 750 flanged 1-3/8" pipes without crossover and a pair of stock peashooters and mount them up. The 750 flanged pipes are readily available. They will work with the spherical type mounts in the head. You may have to get, or make, the earlier rear exhaust mounting plates. You can use the existing crossover pipes if they are good, but they eventually crack where the crossover meets the pipe.

L.A.B. said:

I don't think you need to change the exhaust nuts in order to fit the earlier flanged pipes (even the earlier balanced systems on 850 MkI/II had flanged pipes with the same nuts used on MkIII), what you need to change are the internal parts, the MkIII seating and retaining collets need to be changed for the earlier 850 MkI/II 063990 retaining collets (those collets do not appear to be used with the 'long' nuts used on 750s) and 063995 sealing washers.

I know RGM Motors http://www.rgmmotors.co.uk/ sells a selection of big bore 2:1 and 2:2 (including chrome/black chrome peashooter) systems although their web catalogue does not really show many good photos unfortunately!
Here is one at least of their RGM 2:1 short megga = http://www.rgmmotors.co.uk/images/full/full_471a.jpg

I think they will send you some better photos if you ask?

Click to expand...

L.A.B., thank you as always for the great info. Ok, so it is the internal seating and retaining collets and washers that are different because the older pipes were flanged and the ones I have are not.

So I need to get the exaust system and older 850 MKI/II collets and sealing washers. Got it. You guys rock.

norflog said:

. The 750 flanged pipes are readily available. They will work with the spherical type mounts in the head. You may have to get, or make, the earlier rear exhaust mounting plates. You can use the existing crossover pipes if they are good, but they eventually crack where the crossover meets the pipe.

Click to expand...

I will ditch the crossover pipe simply because I hate the way it looks. I can make mounts or I'll buy new ones, no biggie. I'm pouring cash into this thing already so a few extra dollars will be no big deal. Thanks for the info norflog.

L.A.B. said:

I know RGM Motors http://www.rgmmotors.co.uk/ sells a selection of big bore 2:1 and 2:2 (including chrome/black chrome peashooter) systems although their web catalogue does not really show many good photos unfortunately!

Click to expand...

I must say those polished stainless steel pea shooters look pretty bad-ass. I'm a sucker for shiny stainless steel.

I have seen various offerings from Viking, Toga, Wassel and original Norton stamped mufflers. Some are also longer than others.

The vikings seem to be twice the price of anything else at around $300 a piece. So what is the quality difference if any? I'm one of those guys that like to buy things once so I don't mind spending the cash to get quality. Suggestions?

balance pipe

It is my understanding that the 850 engine was designed for the balance pipe and it helps increase horsepower. That's why I didn't ditch mine. Was I wrong?

Re: balance pipe

Lizard King said:

It is my understanding that the 850 engine was designed for the balance pipe and it helps increase horsepower. That's why I didn't ditch mine. Was I wrong?

Click to expand...

The balanced system supposed to improve the mid-range power slightly, but also causes a slight loss of top-end power (and you don't generally see balanced systems on Commando race bikes), but the main reason for introducing the balance pipe as I understand it was to reduce noise levels, and having used both types I can attest to the fact that the balanced system is quieter.

my understanding of balance pipes is that they were needed for annular discharge cans as fitted to mk 3, but they make no difference with peashooters. I have run peashooters with balance pipe and without and can see no difference other than the noise. Armours make great quality stainless replicas. Dont use stainless downpipes as vibration will fracture them in a very short time

Geoff said:

my understanding of balance pipes is that they were needed for annular discharge cans as fitted to mk 3,

Click to expand...

True, but the balance pipe system was fitted before the annular discharge (black cap) silencers were.

Geoff said:

Armours make great quality stainless replicas. Dont use stainless downpipes as vibration will fracture them in a very short time

Click to expand...

Good to know. I did not realize stainless downpipes were prone to cracking. I will check out Armour. Do you have a link oe e-mail addy handy?

Coco said:

Do you have a link oe e-mail addy handy?

Click to expand...

http://homepage.mac.com/armours/armours.html

When I rebuilt my bike, 850 pre mk 3 1973, I fitted balance pipe stainless type, fine till it cracked up in under 2000 miles. Fred Barlow ex Norton man said "told yer so!". When I put chrome replacements on without balance pipe my question to him was whether I would need to alter carburation, & he said no. So does anyone know why balance pipe was fitted to pre balck pipe system?

All 850s had balance pipes from the begining although the 1973 750s available at the same time (including the catalogue illustrated Short stroke) didn't.

I assume that it can't therefore be related to the Black box and annular discharge silencers as the US market Mk1s and Mk11s had the balance pipe also, not just the European 1As and 11As.

The brochure refers to reduced noise levels on the 850 even though it shows both types of silencer and air box. Could the balance pipe have reduced noise just enough for a critical test ? Wasn't this around the time that they raised 2nd gear by one tooth to quieten it down as it went past the noise meter ?

The balance pipe does reduce the noise, it also improves the mid range grunt which I noticed when I went back to balanced pipes.

Geoff said:

So does anyone know why balance pipe was fitted to pre balck pipe system?

Click to expand...

I did actually mention the reason was for noise reduction on the previous page, and to quote from the *April* 1973 Motorcycle Sport feature on "The New Big Norton" reprinted in 'Norton Commando Gold Portfolio':
------------------------------------------------------------------
"A balance pipe is fitted to all 850s in the interests of noise reduction".
------------------------------------------------------------------
And optional mutes secured by self-tapping screws were available to fix into the peashooter silencers, later peashooters having them welded in position.

79x100 said:

The brochure refers to reduced noise levels on the 850 even though it shows both types of silencer and air box. Could the balance pipe have reduced noise just enough for a critical test ? Wasn't this around the time that they raised 2nd gear by one tooth to quieten it down as it went past the noise meter ?

Click to expand...

As we know the vast majority of even the earliest 850s had the balanced exhaust system, although the increase in the second gear ratio didn't happen until the MkIA model (Sept. 73) along with the annular discharge silencers, black airbox and 22-tooth gearbox sprocket.

Coco,
A little clarification. The Mk3 has sherical inserts in the head to match the spherical end on the pipe. If you use earlier style (flanged) pipes you need to remove the insert. The 850 exhaust "rose" (not really a nut) is shorter than the 750 because the crossover necessitated the split collets to allow the rose to pass over the flange. 750 style pipes allow the rose to be slipped on from the muffler end of the pipe and do not need the collets. Hence, if you elect to use flanged pipes without the crossover, remove the spherical inserts from the head (slip in fit) and either use the 750, long style rose with copper sealing washer, or the 850, short style with collets and copper sealing washer. Alternately, you can use non-crossover, spherical end pipes (available from Raber's, among others) and either style of exhaust rose.

I do not like to use crossover pipes as it is very difficult to find a set that will mate up properly without undue stress on the crossover pipe. This results in cracking at the crossover in short order. I will concede that the power band is slightly different without the crossover, but I'll take the trade off not to replace the pipes every other season.

I tried to find a set of low mount crossover Interstate pipes for a friend and after returning three sets gave up and mounted non-crossovers. One set had the crossover at least half a pipe diameter out of alignment!

Also the spherical (belled) end, non-crossover pipes allow the pipe to be accurately aligned with the mufflers so they stay tight. Assemble the muffler and pipe and bolt up the mounts, then tighten the exhaust rose and they stay.

I have this set up on both my 850 cafe racer and my Interstate and have not had to tighten a loosened exhaust rose in over 10 years. Nor have I had a cracked flange due to misalignment.