The uncrossovering of the 850

Marcelx · Jul 1, 2014

I got my MK3 with unbalanced pipes and straight throw peashooters.
It was really too load, I saw it on the reaction of the people along the street.

I replaced the pipes with balanced pipes and the noise situation improved.
Now I see often a smile

from the people along the road.

There is no difference in the power of the bike, for me the balanced pipes are the better solution and for most people living
nearby the road.

Rohan · Jul 1, 2014

The original peashooters on the first 850 Mk1 bikes with crossover pipes had little 'mutes' (bits of pipe)
that fitted into the very ends of the peashooters.
Held there with little screws. The screw is behind/below, so not generally visible in photos.
Shown in the parts lists.

These quietened the peashooters down to being surprisingly quiet.
Almost too quiet even.
Not a lot of difference in performance by the seat of the pants method, although I didn't explore over +100 mph...
The manual quotes that the main jets need to be reduced in size to suit too,
so fuel consumption could (in theory anyway) be less.

I've used this plan to quieten down some stainless mufflers for another brand bike that were way too loud.
Little bits of stainless pipe neatly shrunk into the muffler exit, did the trick.
Helps keep the rainwater out when it stationary too !

L.A.B. · Jul 1, 2014

Rohan said:
The original peashooters on the first 850 Mk1 bikes with crossover pipes had little 'mutes' (bits of pipe)
that fitted into the very ends of the peashooters.
Held there with little screws. The screw is behind/below, so not generally visible in photos.
Shown in the parts lists.

The 850 MkII peashooters had reduced (1 1/8" instead of 1 3/8") diameter outlets, and these MkII peashooters had a different part number (064609, no longer available)
https://picasaweb.google.com/1130799495 ... 0636546482

Rohan · Jul 1, 2014

I can easily imagine that the Mk1 850 peashooters without mutes wouldn't pass any noise tests,
so the smaller permanent exit diam was probably needed....

phil yates · Jul 1, 2014

Rohan said:
I can easily imagine that the Mk1 850 peashooters without mutes wouldn't pass any noise tests,
so the smaller permanent exit diam was probably needed....

But 40yrs on we can make as much noise as we like with the same machines.
When I registered my USA Fastback they never even wanted it started. They said what a beautiful bike, then did the paperwork. Certainly no noise check.

Phil

concours · Jul 2, 2014

Rohan said:
I can easily imagine that the Mk1 850 peashooters without mutes wouldn't pass any noise tests,
so the smaller permanent exit diam was probably needed....

My 850 with straight through pea shooters and no crossover passed state inspection with db meter last week. :wink:
My other bike shown, but this is the test setup:

Rohan · Jul 2, 2014

Any idea of what noise level standard (dBA = decibels ?) it had to meet ?
And how hard did you have to rev it ?

BTW, seem to recall someone commenting that the tester stuck the tester inside his peashooters !
Not surprisingly, it was fairly loud...

concours · Jul 2, 2014

Rohan said:
Any idea of what noise level standard (dBA = decibels ?) it had to meet ?
And how hard did you have to rev it ?

BTW, seem to recall someone commenting that the tester stuck the tester inside his peashooters !
Not surprisingly, it was fairly loud...

This: http://www.youtube.com/watch?v=2KdYUhH3JSo

If you don't want to sit through it, db limits are shown at 2:58

Onder · Jul 2, 2014

Pardon, Im a bit late to this thread.
Bought a 850 Mk2 four years ago, started it once back then
with repro Dunstalls and crossover pipes and it was loud.
Today torched off the old boat anchor after a four year rebuild. Installed AN single pipes and AN
peashooters. Mother of Divine Grace it is LOUD. Cannot possibly imagine it passing any noise test.
It really is worse on the over run or compression braking.
Had a 72 back in days of yore and I dont remember it being so loud.
Ive had many brit bikes and the current set up really has to be the loudest.
Ill try to run up some mutes!

Nater_Potater · Jul 3, 2014

Onder said:
Had a 72 back in days of yore and I dont remember it being so loud.

It's been said that "If it's too loud, you're too old."

I have to admit that I do not like loud bikes as it tend to promote a stereotype (and I have sensitive ears), but even worse is when the Jap Harley wanna-be's put an open pipe on their "ride" and expect it to sound good. WRONG!

Quiet it down a bit, but don't totally choke it off.

Nathan

auldblue · Jul 3, 2014

"By far the best system for fast road work is separate exhausts joined by a balance pipe,up close to the cylinders."

Norton tuning by Paul Dunstall.

I'm not getting this!

Bob Z. · Jul 3, 2014

Love that vintage catalog photo! Great smile.

The Dunstall 2-1-2 system acts like a long exhaust balance pipe?

Looks like she has been starting the bike on (seems bent) the side stand!
The special centerstand would probably not hold up to too much kick starting either.

Biscuit · Jul 3, 2014

Bob Z. said:
Love that vintage catalog photo! Great smile.

The Dunstall 2-1-2 system acts like a long exhaust balance pipe?

Looks like she has been starting the bike on (seems bent) the side stand!
The special centerstand would probably not hold up to too much kick starting either.

Oh you naughty girl, you've bent my centerstand. Now what shall we do about that? 8)

phil yates · Jul 3, 2014

Onder said:
Pardon, Im a bit late to this thread.
Bought a 850 Mk2 four years ago, started it once back then
with repro Dunstalls and crossover pipes and it was loud.
Today torched off the old boat anchor after a four year rebuild. Installed AN single pipes and AN
peashooters. Mother of Divine Grace it is LOUD. Cannot possibly imagine it passing any noise test.
It really is worse on the over run or compression braking.
Had a 72 back in days of yore and I dont remember it being so loud.
Ive had many brit bikes and the current set up really has to be the loudest.
Ill try to run up some mutes!

I don't like overly loud bikes, especially on long distance rides, but the pea shooters on my MkIII certainly are no noisier than my 72 combat was. A little more subdued I'd say. I'm sure they wouldn't pass any modern noise test, but thank god for that. Your Norton would sound like a koala bear with asthma. Or one of those dreadful flashy things you see whizzing about making wheezy noises.

Phil

phil yates · Jul 3, 2014

Biscuit said:
Bob Z. said:

Love that vintage catalog photo! Great smile.

The Dunstall 2-1-2 system acts like a long exhaust balance pipe?

Looks like she has been starting the bike on (seems bent) the side stand!
The special centerstand would probably not hold up to too much kick starting either.

Click to expand...

Oh you naughty girl, you've bent my centerstand. Now what shall we do about that? 8)

Tie it to the handlebars overnight with a rubber band. Apparently it will be a lot firmer in the morning. But it will be a looooong night!!

Great set of handlebars in the photo. Don't know how the rubber band stays on.

Phil

acotrel · Jul 3, 2014

Rohan said:
How much that cross over pipe was just marketing speak and how much it actually provided 'more torque'
has been the subject of a lot of speculation over the decades.
We'd welcome a true back-to-back comparison from someone committed to providing real science to the discussion...

If the motor is running and exhausting through both pipes at each firing, might not the reduced back pressure allow the motor to develop more power at certain revs ? The other way to go is with tuned separate pipes and that is usually louder. Also the power band is usually much more pronounced. In the end it depends on how you intend to use the bike and what noise laws apply. You could fit a two into one pipe as I do on my racer. It works extremely well, loads of torque - however your neighbours would start taking up petitions against you.
You really love those dynos, Rohan - how many hot vintage bikes have you ever ridden ? I don't believe you really know when you've achieved a performance improvement by riding the machine.

acotrel · Jul 3, 2014

auldblue said:
"By far the best system for fast road work is separate exhausts joined by a balance pipe,up close to the cylinders."

Norton tuning by Paul Dunstall.

I'm not getting this!

What will the bike in the photo rev to with that skinny outlet pipe after the collector ? It might look good, however I will bet the motor has no top end. The dual pipes with the crossover is probably a better system than most if you want a quiet road bike and still have a bit of performance. The backfiring caused by the air leaks would drive me insane.

Rohan · Jul 3, 2014

acotrel said:
What will the bike in the photo rev to with that skinny outlet pipe after the collector ? It might look good, however I will bet the motor has no top end. The dual pipes with the crossover is probably a better system than most if you want a quiet road bike and still have a bit of performance. The backfiring caused by the air leaks would drive me insane.

Goes to show, Alan - that Dunstall exhaust was part of Dunstalls package that gave THE fastest Nortons back when they were new - was 133mph wasn't it ?
(With suitable gearing).(Maybe that was the 810cc model...).
Not sure, but that pipe was mostly one piece, so not many place to leak from. (?).

It does look rather low, and the stock centrestand can't be fitted either.
(there was a custom Dunstall centrestand ?).

Seat of the pants performance measuring is very possible.
When I used to commute to work in the big smoke, a set of timed traffic lights used to be a measure of how in tune it was.
A set of linked lights not very far apart was rather quick - you have to get through before it went red, or wait quite a while.
Good acceleration test - and you had to be head of the queue.

Time Warp · Jul 3, 2014

There was plenty of room to put the balance pipe back under the transmission same method that Ducati and Moto Guzzi used, maybe the isolastic system would have been a problem with the primaries joined so far back vibration wise and cracking.
Then again maybe not, looks like it was never tried to see.

As far as the noise law in this state (NSW) you might get registration but you can be stopped anytime and could then get a letter requesting your bike be re checked.
The law actually says the system must be that which was fitted at the factory, that might be an out for the Commando if you have the Norton embossed peashooters.

auldblue · Jul 3, 2014

After a night in the workshop working with solvents without adequate ventilation I bought this on fleabay.
When fitted I thought it looked pretty ropey, but took the 750 out anyway althiugh I had bounced the forks a bit it cracked of the front mudguard and nearly put me down dent still in the mudguard .
Could have been my imagination but I thrashed it up over 90 and it seemed want to go better and have more left over 75
Than with single pipes. But not clever only using back brake!

For hobot ,it was the farm road with a dusting of gravel only doing about 30 when had mudguard impact so was not a full handful of TLS. Only damage dented mudguard and whiplash of the sphincter other than that good to go.

This photo was staged no animal or motorcycle were harmed in its production.

The uncrossovering of the 850

Marcelx

Rohan

L.A.B.

Moderator

Rohan

phil yates

concours

Rohan

concours

Onder

Nater_Potater

auldblue

Bob Z.

Biscuit

phil yates

phil yates

acotrel

acotrel

Rohan

Time Warp

.......back to the 70's.

auldblue

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