Max sustainable RPM?

If the buying public wanted motorcycles that could do 10 to 100mph in top gear, why did designers waste their time with anything more than a two speed gearbox?

With a bit of tweaking they could probably have done away with the gearbox altogether, the bean counters would have loved it, given them a bonus!

To think I started following this thread when it was new.....and with no answer in sight, how did it get here? Happy Monday Fellas. ;)
 
There are a few answers in there. I guess it comes down to who you want to believe along what number you would like.
I don't think anyone has done a deliberate test of maximum sustainable rpm. You could do this by taking a good Commando out and running it for a couple of hours at 4500 rpm first off then increasing 100 rpm with every 2 hr test until she comes apart.

Any volunteers? 🙋‍♀️

Glen
 
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worntorn said:
There are a few answers in there. I guess it comes down to who you want to believe along what number you would like.
I don't think anyone has done a deliberate test of maximum sustainable rpm. You could do this by taking a good Commando out and running it for a couple of hours at 4500 rpm first off then increasing 100 rpm with every 2 hr test until she comes apart.

Any volunteers? 🙋‍♀️

Glen
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Ya, I'll do one if you will - can't prove anything with just one :)

If we did ten some expert here would say the test was not valid - and, they would be right!

I stick by what I said over 150 posts ago (post #4). IMHO, it's not an answerable question! And, even your test doesn't change that because it would have to be run in every conceivable condition with a minimum of two identical bikes and in each configuration (850 Mark 1, 1A, 2, 2A, 3.) I left 750s out since the OP did.
 
Without being more specific, it's an unanswerable question. Any revs and in the end you'll need a rebuild. The answer is probably different for everyone.

Maybe the equation is:
Max enjoyment = amount of fun / miles between rebuild.
30mph is probably a long time between rebuild, but not very enjoyable / exciting. 120mph is perhaps the opposite. The optimum being somewhere in between depending on your riding style, your local roads, your ability working on your bike, how deep your pockets are......?
 
The maximum sustainable RPM depends on the balance factor. - Whet is complicated about that ?
Commandos are not designed to rev high. If the blurb says 5000 RPM - that is what it is.
The Norton factory could not risk stating a higher number and having a multitude of failures.
A 650ss or AtlaS can rev to 7,500 RPM consistently, without faiilure but the crank has a higher balance factor.

With a high balance factor, the Commando will rock backwards and forwards while it is idling.
When the Commando does that, it is not as smooth as a Honda CB750. But a Honda CB750 does not go stop or handle, anywhere nears as good as a Commando.
When you are selling motorcycles to Mods - what matters ? Do you want a throb or a buzz ?
 
Maybe have a poll of opinions
I'd say I'd say 5000 rpm would be sustainable
 
acotrel said:
.... it is not as smooth as a Honda CB750. But a Honda CB750 does not go stop or handle, anywhere nears as good as a Commando. ....
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I love my Commando. Probably my favourite bike. But I have both of these bikes and ridden them back to back. I don't agree. The Honda isn't as smooth as the Commando. I have stock brakes on the Honda and they're almost as good as the non standard front disc, pads and aftermarket m/c bore on my Commando. In the twisties, the Honda is more flickable than the Commando. No doubt about that. The suspension is better on my Commando, but after I replaced my rear shocks ((Hagon).

I expect it's not a popular observation. I didn't expect that result either, just the way it is.
 
acotrel said:
The maximum sustainable RPM depends on the balance factor. - Whet is complicated about that ?
Commandos are not designed to rev high. If the blurb says 5000 RPM - that is what it is.
The Norton factory could not risk stating a higher number and having a multitude of failures.
A 650ss or AtlaS can rev to 7,500 RPM consistently, without faiilure but the crank has a higher balance factor.
Click to expand...
Let me see if I have this right, two bikes, both MK2 850, both 19-tooth front sprocket, stock balance factor, both Interstate with a full tank, hot day, 100 miles:
Bike 1: Stock with a 100lb rider on the Autobahn holding the bike at 5000 rpm with a 19-tooth sprocket.
Bike 2: 12:1 Compression, 2S cam 300lb rider riding beside the other bike on the Autobahn

You're saying that the bikes will both be just fine. If so, please explain how the two engines are both putting forth the same effort and remaining the same temperature.
 
acotrel said:
...................If the blurb says 5000 RPM - that is what it is.
The Norton factory could not risk stating a higher number and having a multitude of failures.
Click to expand...
Umm, I seem to remember Norton sold a particular model where they did mention high speed.....and they suffered badly from a multitude of failures!
acotrel said:
When you are selling motorcycles to Mods - what matters ? ...............
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I remember the Mods, they were all about style, buzz cut hair, nice suits and clean fingernails, what would have mattered is keeping clean!
 
SteveA said:
Umm, I seem to remember Norton sold a particular model where they did mention high speed.....and they suffered badly from a multitude of failures!

I remember the Mods, they were all about style, buzz cut hair, nice suits and clean fingernails, what would have mattered is keeping clean!
Click to expand...
In the UK Mods ride scooters
Maybe I'm missing something?
 
Mart UK said:
Without being more specific, it's an unanswerable question. Any revs and in the end you'll need a rebuild. The answer is probably different for everyone.

Maybe the equation is:
Max enjoyment = amount of fun / miles between rebuild.
30mph is probably a long time between rebuild, but not very enjoyable / exciting. 120mph is perhaps the opposite. The optimum being somewhere in between depending on your riding style, your local roads, your ability working on your bike, how deep your pockets are......?
Click to expand...
If the blow up is spectacular enough there can be nothing left to rebuild. I recall one engine blow up that was shown on this site a few years back. Nothing was left , even the head was destroyed. I cannot recall for certain the cause of that one, but I think high rpm was involved.

Glen
 
worntorn said:
If the blow up is spectacular enough there can be nothing left to rebuild. I recall one engine blow up that was shown on this site a few years back. Nothing was left , even the head was destroyed. I cannot recall for certain the cause of that one, but I think high rpm was involved.

Glen
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A mate often tells me the story of being alongside a Seeley commando on the track when the engine blew
He said there was nothing useable out of the motor
But it was doing extremely well just before it blew
 
baz said:
A mate often tells me the story of being alongside a Seeley commando on the track when the engine blew
He said there was nothing useable out of the motor
But it was doing extremely well just before it blew
Click to expand...
They always do, and that is why I am about to strip an apparently fully functional motor! ;)
 
baz said:
In the UK Mods ride scooters
Maybe I'm missing something?
Click to expand...
I think we both are, that's what I meant by Mods needing something they can ride without getting dirty!

As for what Al is on about? An American saying Mods would probably mean Moderators! But who knows what an Australian might mean by the Mods!
 
marshg246 said:
Let me see if I have this right, two bikes, both MK2 850, both 19-tooth front sprocket, stock balance factor, both Interstate with a full tank, hot day, 100 miles:
Bike 1: Stock with a 100lb rider on the Autobahn holding the bike at 5000 rpm with a 19-tooth sprocket.
Bike 2: 12:1 Compression, 2S cam 300lb rider riding beside the other bike on the Autobahn

You're saying that the bikes will both be just fine. If so, please explain how the two engines are both putting forth the same effort and remaining the same temperature.
Click to expand...
At those speeds, the riders fat arse is a small portion of the power loading. Punching the hole in the wind is the lion's share of resistance.
 
concours said:
At those speeds, the riders fat arse is a small portion of the power loading. Punching the hole in the wind is the lion's share of resistance.
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Yes, if you see me next to a 100lb rider (probably no more than 5'5" and super skinny) it's pretty clear I'm MUCH harder to drag down the road.

The rest of the scenario was about the engine itself. Saying that nothing matters other than the crank balance factor is comical to me!
 
It is kind of humorous that we can go back and forth for pages over the exact point that our old bikes will blow up!
They don't get to do that on the R1 forum. The damn things have a rev limiter that is set on about one zillion rpm and to make matters even worse, they can handle it!

Glen
 
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