Max sustainable RPM?

Gotta love it! In reality though, the Norton twin is really a good, durable engine considering that the design goes back to the 40's. I've had engines in the shop that were completely and utterly worn out, yet they were running ok. And the Commandos are lovable bikes to own and ride. I test rode a new Guzzi V100 Mandello the other day. It was pretty nice, but rode like a truck, you felt every tiny bump. I was happy to jump on the MKII and ride home in style and comfort.

The Mk3 is my most comfortable bike over rough /broken asphalt. I don't know why it's better than the Thruxton R with its high end Ohlins rearshocks and Showa Big piston forks, but it is.
Must be the 30lb weight of that MK3 e-starter helping!
The Commando will sustain ticket yielding speeds anywhere I ride.

Glen

worntorn said:

The Mk3 is my most comfortable bike over rough /broken asphalt. I don't know why it's better than the Thruxton R with its high end Ohlins rearshocks and Showa Big piston forks, but it is.
Must be the 30lb weight of that MK3 e-starter helping!
The Commando will sustain ticket yielding speeds anywhere I ride.

Glen

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Are you by any chance headed to the Norton rally in Washington this summer?

milfordite said:

Gotta love it! In reality though, the Norton twin is really a good, durable engine considering that the design goes back to the 40's. I've had engines in the shop that were completely and utterly worn out, yet they were running ok. And the Commandos are lovable bikes to own and ride. I test rode a new Guzzi V100 Mandello the other day. It was pretty nice, but rode like a truck, you felt every tiny bump. I was happy to jump on the MKII and ride home in style and comfort.

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When I built my Seeley 850, I never beieved in that motor. However I am now surprised that it is so right. It is competitive in road races, where it should really not be competitive. A close ratio gearbox makes a significant difference. I think that motor is a gem. It really responds well to tuning. I might have an advantage in that I have learned the hard way, but that motor is excellent. When I was young, I led an Allpowers race in which there were Z900 and H2. I know how fast a motorcycle of that era has to be, to get up front.
To me the Commando crank looks horrendous, but it really works well. My bike sat unrasced for 25 years before I tried it in a road race, simply because I could not beieve it would ever be fast enough. My old mate rode it a couple of times and really loved it. He was sillier than I am. When I race, I do not stick my neck out.

When you build a race motor, the rod length to stroke ratio and crankshaft weight, and the cylinder head characteristics are critical factors,. You cannot get them right through simple speculation.
The same sort of thin applies to the featherbed frame. You cannot just make one out of a design in your head and expect it to work well. I don't know where Colin Seeley got his smarts. - he was a sidecar guy. I think the McCandles brothers did a lot of work.

worntorn said:

The Mk3 is my most comfortable bike over rough /broken asphalt. I don't know why it's better than the Thruxton R with its high end Ohlins rearshocks and Showa Big piston forks, but it is.
Must be the 30lb weight of that MK3 e-starter helping!
The Commando will sustain ticket yielding speeds anywhere I ride.

Glen

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Glen the Thruxton R has sport suspension and would feel rough on broken asphalt, my Thruxton S is completely different it love rough as well dirt roads and rides through it quite comfortable as well at higher speed when on the dirt but my Norton being a light weight bike is also good on rough and dirt roads and we do go through a few dirt roads on some of our great rides my mates take it slow and easy but they are always eating my dust lol and are surprised in how well my Thruxton S handles it it has the same front end as my old AC Thruxton, well similar anyway.

milfordite said:

Are you by any chance headed to the Norton rally in Washington this summer?

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I'm still deliberating that. A group of us are doing a ride to south eastern BC the week before and some are going to the Norton Rally on the way home. If I can find the time I sure will.

Glen

Would it be true to say that the crankshafts of the 650SS, Nc, N15 and the Atalas are all the same as the Commando crank except for the extra balance hole which has been bored into the heavy side of the Commando crank to make it run smooth at low RPM ? - If it is true, who sells those earlier crankshafts ? There might be an easy way to get more performance out of a Commando. An earlier crank combined with a 6 speed TTI box with the kickstart, might be a better answer than playing with compression ratios and camshafts.
The earlier motors ran safely to well over 7000 RPM, and the crankcases were probably much the same as with a Commando

acotrel said:

Would it be true to say that the crankshafts of the 650SS, Nc, N15 and the Atalas are all the same as the Commando crank except for the extra balance hole which has been bored into the heavy side of the Commando crank to make it run smooth at low RPM ? - If it is true, who sells those earlier crankshafts ? There might be an easy way to get more performance out of a Commando. An earlier crank combined with a 6 speed TTI box with the kickstart, might be a better answer than playing with compression ratios and camshafts.
The earlier motors ran safely to well over 7000 RPM, and the crankcases were probably much the same as with a Commando

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The earlier crank fits, but the rotor keyway is way off by about 140 degrees so the timing marks do not work. I don't know how it would run, when I found the wrong crank installed I changed it. Here's a thread on it: https://www.accessnorton.com/NortonCommando/problem-i-havent-seen-before.35719/#post-591213

When I built my 850 motor back in 1979, I probably approached it with the wrong mindset. THere is a major difference between Japanese and Brtish motorcycles. When the Japanese bring out a new model, it is often a complete new design, they don't worry so much about spares compatbility. British motorcycles are usually part of a development progression. I only had a few acquaintances who had Norton twins - a Dominator 88, a Manxman 650, an Atlas and a Commando 750. Bob Rosenthal had the Atlas and had won Allpowers A grade races with it. But the first Atlas which came to Melboure broke its barrel flange, so I stopped thinking about them.
My 850 was never a serious attempt to do anything, however when I eventually raced it, I was pleasantly surprised when I found out how good it is. The crankhaft has always been a problem, but it has not failed yet.

I look at what kids face these days and it makes me sad. I lived in the best time ever. In the old days there wre no speed limits on Australian country roads We used to do iterally 100 MPH on city streets, because the cops had to follow you for about half a mile to book uo. So if you saw them, all you hade to was brake hard and pull-up at the roadside, before they followed you for any distance.
I was talking to a young guy a few weeks ago. He told mehe was the motorcyclist the cops saw doing 280 KPH on the Hume Highway. Apparently they had gone to his home purportedly looking for drugs. But they could not prove he had been doing 280 KPH, so he was not charged. But realistically, you cannot do that stuff these dasys.
In the olds days, masny car drivers werec drunk, and theroad toll was extremely high. These days the casrs are better and so are their drivers, and we all drive slower, and necver under the influence.

It is very strange, -my whole life as a scientist has been influenced by motorcycles. They helped me to think differently. Whenever I have a problem in a workplace, I can always fix it.
In my last full time job, my boss wass a young engineer. I showed him my Seeley 950. All he sais wad 'I am impressed'. I know his capabilities and I don't think he could have biult my bike.

marshg246 said:

The earlier crank fits, but the rotor keyway is way off by about 140 degrees so the timing marks do not work. I don't know how it would run, when I found the wrong crank installed I changed it. Here's a thread on it: https://www.accessnorton.com/NortonCommando/problem-i-havent-seen-before.35719/#post-591213

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I have posted aresponse on the other thread. If the flywheel on your early crank has not been drilled for rebalancing, I might like to buy it. I renove the bit where the rotor fits, anyway.

For sure you are asking a lot more of the engine when you ask it to propel you and the bike along at 102 mph (23 tooth) vs 89 mph (20 tooth), even though the rpm is identical in both scenarios.

Why? Unless by engine we are talking multiple aspects not covered by what I consider"engine", how would it be different. Engine under load in both cases..and 4000 rpm is 4000 rpm, no matter what the wheels are doing. Pistons, valves, cams etc all turning same speed in both scenarios. What am I missing?

trappnman said:

For sure you are asking a lot more of the engine when you ask it to propel you and the bike along at 102 mph (23 tooth) vs 89 mph (20 tooth), even though the rpm is identical in both scenarios.

Why? Unless by engine we are talking multiple aspects not covered by what I consider"engine", how would it be different. Engine under load in both cases..and 4000 rpm is 4000 rpm, no matter what the wheels are doing. Pistons, valves, cams etc all turning same speed in both scenarios. What am I missing?

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Same RPM, higher load = more fuel required = more heat, more pressure in each power stroke. You simply cannot get something for nothing!