Max sustainable RPM?

KiwiShane said:
I'm glad you got one ...as it will save me fitting one..🤣
Practical solution👍and when ya hit a swam of bees etc ...then im jealous
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Not the prettiest thing
But it does what I need
 

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baz said:
Not the prettiest thing
But it does what I need
Click to expand...

Practical as mate 👍...all the waterside workers years ago down here that did shift work...rain or shine all had them fitted to their motorcycles...
The amount of riders this year at our west coast meet up that didn't turn up because of rain ...are now called disprines 🤣
 
I am not a big fan of fly screens. I rode a lot of 70s and 80s bikes with a variety of them fitted an they always seemed to negatively affected the handling at speed.
 
I wish I could remember the actual quote, but it went something like this:
"The Commando is a fine bike if you can get past the idea that when its running its constantly eating its guts".

Anybody know the actual quote?
 
Stephen Hill said:
I wish I could remember the actual quote, but it went something like this:
"The Commando is a fine bike if you can get past the idea that when its running its constantly eating its guts".

Anybody know the actual quote?
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Sounds about right 🤣🤣🤣
 
Isn't that true of all motorized vehicles?
The Commando is no different except it might be a lot closer to the edge of destruction than most modern bikes. That is likely true with most older British bikes.
It's just something to take note of and live with.

Glen
 
There are two limits. One is max power and the other is when your engine starts breaking. Hopefully the max power point is before the engine breaking point. It would be nice to know both
 
TomU said:
There are two limits. One is max power and the other is when your engine starts breaking. Hopefully the max power point is before the engine breaking point. It would be nice to know both
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It sure would!
Max power on a stock 850 is listed as 5800 rpm.

I guess when the cases have cracks you have gone too far somehow. Unfortunately that's about it for that engine, unless you really enjoy Roulette.

Glen
 
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Never heard of any such quote ..
But... I've never heard any one that purchased one for road use in the 70's say they were gutless.
 

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TomU said:
So that's the effective red line
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I don't think so. That's where the HP curve peaks. It doesn't mean it can do that all day, or that you should shift there for maximum performance. In fact it might be happier at lower power at 6000 due to combustion induced stresses and maybe sympathetic vibrations being lower, although it's probably not likely.
 
TomU said:
So that's the effective red line
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The Norton manual lists peak power for the 850 at 5800 rpm, peak torque (56 ft lbs) at 5000 and warns in capital letter
" DO NOT EXCEED 7000 RPM"
I used 6500 as a shift point when racing a hot 750 that rolled on a couple of seconds before me.
That puts the rpm just after the 1 to 2nd shift at 4200, 2nd to third at 4800 and 3rd to fourth 5300.
Next match I will drop that 3rd to 4th shift rpm to 6200 so that it hits 3rd right at max torque.
As it was, the MK3 did very well against a bike that, on paper, should have smoked it.
Going back to sustained max rpm, Norton doesn't give us a number for that.

Glen
 
As the OP, I'm glad to see all of the opinions! As I said, for a stock bike, I still think 5K is a reasonable limit for holding it there between gas stops. That said, I still run mine at 4 or 4,200 rpm all day with a 22 tooth sprocket. I use Royal Purple HPS 20/50 on trips, especially when it's going to be hot. When I rode to the Oregon rally years ago, it was 105 degrees F coming up the coast, in Oregon , and in Kansas on the way home. Glad to have the extra protection!
 
If peak torque is at 5k, producing the most power with the least effort, I opine it should run all day there.
 
I'm so glad New Zealand doesn't have such boring road ways that require the thought of a fixed type throttle opening and it is why the Norton is best suited to most of NZ and England's roads.
 
North America is a big place. Sometimes you have to cover a lot of ground to see a new destination. On the west coast we rarely have to run on the freeways and interstates. Sometimes it's necessary for half an hour or so. Then it's nice to have a bike that can handle the 80 mph speed limit seen in some of the US states. The Commando is OK for this when needed.
Most of the time though, we are on 60-70 mph posted old 2 lane highways that wind along. The Commando works great on those. It isn't working overly hard, but it is working.
Some of those really twisty roads in NZ would be best ridden with a lightweight 250! You don't even need the hp of a Commando however a bike with lower weight would be a plus.

Glen
 
MichaelB said:
If peak torque is at 5k, producing the most power with the least effort, I opine it should run all day there.
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Hi Michael,
I'm not quite sure of the logic you are using when you say it should be able to run at peak torque (5000rpm) all day?
Certainly that should be the goal of an engine designer but I’m not sure if it applies to our Nortons.
Peak torque is a function of geometry, tuning etc where maximum sustainable rpm is a function of materials and construction. The two are totally different things.
I think this interesting discussion can really be defined as determining the limits of a 360’ four stroke engine (without counterbalance shafts) in both size and horsepower output. Simply put, considering the materials and construction techniques available, an 830cc parallel twin engine is difficult to make reliable and have acceptable vibration above a certain rpm. Demands for power output in the Norton’s case has put the maximum torque rpm at the upper limit of it’s continuously reliable rpm range. This would be disastrous for say a truck engine or even an underpowered car engine that in everyday use spends a lot of it’s time approaching maximum engine output in normal operation but could be ‘got away with’ on a high power motorcycle.
I guess Norton could justify this shortcoming at the time by stating that because of the high power output of the engine the average rider would have no need to spend extended times at high rpms, simply using the power for short bursts.
This would probably be the case on the slower British roads in the 60s before freeways were built. Not the case with bikes ridden in Europe or America.
Out of interest, one of my other strange passions in my 1965 Humber Imperial car. It has a beautifully smooth and powerful (for its day) engine and is capable of quite high speed touring but it feels grossly under-geared (19mph/1000 rpm, max rpm 5300). It has oodles of torque and could easily accept higher gearing but I guess in its day there were not that many roads available to make use of a better ratio (Note: overdrive was available on manual versions). It feels a little busy at 110km on Australian freeways although it is capable of over 160km/hr
So, in brief, our motorbikes are (excellent) compromises. I’m sure Norton would have liked to have made the motor more reliable and rideable at higher rpms to increase power and compete with the Japanese onslaught but cost and basic geometry and harmonics were against them.
I should point out that where I live in Australia the roads are fast and mostly remote from police. Potholes and wildlife being our biggest problem. Riding my Commando, especially in the company of friends on modern ultra sports bikes developing multiples of my horsepower the speed I ride at is a constant compromise between what I want to do, what is reasonably safe and what I think is acceptable to the motor. I tends to settle for around 5000rpm or approximately 80mph. I suspect the bike would be happier below 4500, but hell, it’s a pampered bit of Pomie iron, even it occasionally has to work for a living😉
Alan
 
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