So many new upgrades available these days

As I mentioned I have the cNw electric boot on mine.
I press the button once a month to test that it still works. other than that I always kick it (much to @Fast Eddie 's annoyance)
The button is for if/when my knee won't do the job any more

ashman said:

It will never happen it will be with me till I leave this world, as I say I think positive all the time I plan on making it to 105 and I am not leaveing till after that and hopefully I still be kicking my bike, thinking about not riding it from injuries is just not in my thoughts, my bikes will be handed down to my youngest daughter but by then there might be no petrol around to ride it, I just don't think about these things, I take each day as it comes and have a positive attitude with life.

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Glad you are keeping your bike for your daughter

robs ss said:

As I mentioned I have the cNw electric boot on mine.
I press the button once a month to test that it still works. other than that I always kick it (much to @Fast Eddie 's annoyance)
The button is for if/when my knee won't do the job any more

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Design redundancy goes against the grain…

I bought an electric start which is based on an angle grinder. But even if I did not have it - I bump-started my bikes when I was younger and I am not dead yet. You are only as old as you are in your head. I've had a piece of bone broken off inside my right knee. My only other injury was a broken chromo clavicular joint. I had a knee operation and learned to walk again. If I have to kicj-start a motorcycle, I just do not go at it like a bull at a gate. Many people do it too quickly. Any motor can kick back, but if you always keep pressure on the kick start, you can hold it. If you bounce around, that is when you get bitten.

If your motorcycle is properly tuned, it should always start first kick.

My doctor said I have surprisingly good knees for a 75 year old. I intend to keep it that way and ordered my e starter today. Having kick and electric starters is a real luxury, IMHO.

jamesp said:

My doctor said I have surprisingly good knees for a 75 year old. I intend to keep it that way and ordered my e starter today. Having kick and electric starters is a real luxury, IMHO.

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As I always say, good if you have the money but my Norton is my light weight hotrod built for lightness and handling, adding a big battery and starter is just not on the cards no matter what, wouldn't even have the room for a big battery.

The most important upgrade it to reduce the stress/vibration of your Norton so you don't crack the cases or crank. That means reducing the reciprocating weight. Even more important if you add performance or increase the displacement.

Well yes, I understand that you sell that stuff. Maybe it's needed for racing, but really you also need to throw the rest of the engine away for racing. And the gearbox.
For the road I don't believe the standard pistons and rods need to be changed out. No harm if you want to, but totally unnecessary.

My Commando still has all of its original internals that it left the factory with almost 50 years ago. It works just fine.
Same old pistons rings valves, crank, conrods etc.
It received a new head gasket about 15 years ago, that's it for engine work.
Why would I tear that apart to replace major items at great expense?

Glen

I agree with your observation jseng1. Over the years I have rebuilt a variety of different power plants and internal upgrades usually made me smile when I stuck my foot in it twisted it to WOT.
One issue I always struggled with is putting all those beautifully machined/finished parts inside of an engine block or casing or housing.
Much of the time I wanted to put them on the mantle above the fireplace or on display in the center of the family room table or under a display light in my shop.

When I bought my Commando the first thing I did was pull the engine and break it down for inspection.
I lightly honed the cylinders and replaced the rings and I only did this because it had been sitting for 44 years.
The rest of the guts all spec'd out. Now that the rest of the bugs have been squashed it remains a reliable and rideable motorcycle.
I still have a functional kick starter in place but as stated in another thread I am quite happy with pushing the button.

Lineslinger said:

I agree with your observation jseng1. Over the years I have rebuilt a variety of different power plants and internal upgrades usually made me smile when I stuck my foot in it.
One issue I always struggled with is putting all those beautifully machined/finished parts inside of an engine block or casing or housing.
Much of the time I wanted to put them on the mantle above the fireplace or on display in the center of the family room table or under a display light in my shop.

When I bought my Commando the first thing I did was pull the engine and break it down for inspection.
I lightly honed the cylinders and replaced the rings and I only did this because it had been sitting for 44 years.
The rest of the guts all spec'd out. Now that the rest of the bugs have been squashed it remains a reliable and rideable motorcycle.

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So your Commando engine is still all stock internally?

I should have mentioned it had less than 10K miles when I bought it.
Valve seals and rings are not original since I replaced them.
I reseated the valves for obvious reason upon opening it up, but yeah, I tore it down and visually inspected it and then took it all to my engine building machinist friend and we dug deeper. I followed his recommendations. This bike/engine had been sitting a long time and common sense dictated a tear down. I don't like performing the same job twice.

I bought my 850 motor in 1978 for $1300. I repaced the big end and main bearings and the rings, rebalanced the crank and had the cam given a mild regrind. I tapered the starts of the inlet tract, and cleaned up the ports. Apart from those things nothing has been done to it. It has not been raced very often, but on methanol, it is fast enoughh - surprisingly.

Those who go higher RPM with a hotter cam in a stock motor or to larger displacement such as 920cc with heavy pistons on stock rods and cases are placing a hell of a lot more stress on their motor. That means they have to be more careful how high they rev it or risk catastrophic failure. Every time you rev up such a motor you have to watch the tac and shut it down before it blows up. You live in perpetual fear of breaking a crank or cases or rod. The stock aluminum rods will fatigue. The cranks can crack at the sharp corner where the PTO shaft meets the flywheel cheek. The cases can develop radial cracks around the left side main bearing. You are always at risk. This happens on street bikes as well as race bikes. And its all because of the increased downward force created during the power stroke combined with the severe vibration/stress caused by excessive reciprocating weight (which increases exponentially with more weight and higher RPM). The solution is obvious - reduce the reciprocating weight and enjoy a smoother more reliable riding experience. You have your choice - more vibration and stress or less vibration and stress.

I don't believe this is a big issue with street Commandos.
A good friend just rebuilt his 1973 850. He has owned it since new and it was his only transport until 1990.
He put 128,000 miles on it with only a top end rebuild at about 70,000 miles as it was getting down in compression.
This time around it got a more complete rebuild but the original rods went back in.
He rides about like I do, a bit frisky at times, but no track riding.

You really can't fault a rebuild interval like that on an old air cooled engine.
No blowups due to heavy pistons or weak factory rods, bad crank, just 128,000 miles of riding with basic maintenance. Now it is all rebuilt and ready to do another 128,000 miles.
Not many of us will get to ride that far!

Glen

Glen
You recently posted info about your 920 motor and that you had to keep the RPMs lower because you were concerned about stress and failure. I'm not sure but I think you said 5000 RPM. Is that what you recommend to anyone putting heavy 920 pistons in an otherwise stock motor?

My 850 motor has normal 9 to 1 compression pistons, but I run methanol and adjust the timing and carburation to suit. My crank is rebalanced to 72 %. At 7000 RPM, it does not vibrate - it runs smoth and feels as though it would rev to 8000 RPM easily. To rebalance my crank, I simply screwed a steel plug into the hole in the counterweight of the crank. If it comes out, I am dead. It is a tight fit and is in there with blue Loctite.
People who believe they need high compression are de;luded. The comp. ratio, ignition advance, fuel octane ratio and carb jetting are all in balance. If you change any one of those factors, the balance must be restored, by adusting at least one of the others. Then you are back where you started from.
The way I tune, is to choose an ignition advance to suit the fuel, then jet to suit it - starting rich then leaning off. Bob Rosenthal does it differently. He uses the oxygan sensor to get the jetting tight when the bike is on the dyno, then he moves the timing unti he gets maximum torque. Either way produces the same result.
But for road use - ?
The only reasons I use methanol fuel for racing are - because the jets are twice the size of petrol jets, it is easier to get right. And the motor runs cooler. I have run a motor which has been jetted right for methanol, and the same motor which has been jetted right for petrol - there is only a very slight difference.
In the 1950s Australian riders who went to the UK, found the Brit's Manx Nortons were as fast on pool petrol, as theirs' were in Australia using methanol.
There is a problem whichever fuel you use. If you are the slightest bit over-rich, you take the edge off the motor. If you gain a torque improvement, you often do not know it until you raise the overrall gearing.
Piston weight is if critical importance when the motor is revving at 7000 RPM. Every time the piston reaches the top of the stroke, it reverses direction. Longer conrods give slower rock-over.
If I was going to change anything in my motor, I would buy Jim Schmidt's long rods and light pistons.

There is a thing with 650 Triumph high comp. pistons. If you look at 12 to 1 comp. Triumph pistons after they have been used for a long time, there is always coke on the crowns on the sides which are away from the spark plug. At top dead centre when the motor is runnig, on every second stroke - both valves are open and gas flows through the combution chamber and into the exhause pipe - then gets stuffed back into the combustion chamber. (Kadency Effect). A high crown on the piston obstructs that flow.

jseng1 said:

Glen
You recently posted info about your 920 motor and that you had to keep the RPMs lower because you were concerned about stress and failure. I'm not sure but I think you said 5000 RPM. Is that what you recommend to anyone putting heavy 920 pistons in an otherwise stock motor?

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I built that motor for maximum power in the midrange. For that the stock cam is the clear winner. According to Norton, stock cam gives max torque at 5,000 and max bhp at 5800 with the 850.
I imagine it is similar for the 920.
With that in mind, I keep the revs to about 6 k with both bikes.
I used to sometimes rev the 850 higher when after rapid acceleration. This was a mistake. It gets down the road quicker if the shifts are done no higher than 6200 rpm.
So there's no need for the high rpm or to build the engine to withstand high rpm with the stock cam as you are just revving into a lower power band, stressing the engine for no gain.

The 920 is a bit of an unknown. Jim Comstock has had to fix at least one of these by putting it back to 828 size. Iirc that problem wasn't caused by piston weight, it was due to bores going out of round. I think that can be an issue with 920s, even alloy Maney 920s. I recently ead of one of those being converted back to 828 as the 920 Maney cylinders were no longer round and causing all kinds of running issues, puking oil etc.
Time will tell with my 920, it's an experiment. At present it has loads of power and revs quickly to 6 k, at which point I shift and go again.

As I see it the stock Norton engine is sufficiently weak that any mod which moves the Rev range up is asking for trouble. That's what did the Combat in.
The 850s are a little stronger but still probably best kept to around 6k or below. The stock cam is working best here too.

If want to build a high performance Norton lookalike motor, use stronger cases , crank, lightweight pistons, TTI box etc. Don't leave any Norton in the engine at all. OK maybe the valve inspection caps!
Half way in between isn't so great if the expectation is to routinely use 7 k rpm or so.

Glen

worntorn said:

I built that motor for maximum power in the midrange. For that the stock cam is the clear winner. According to Norton, stock cam gives max torque at 5,000 and max bhp at 5800 with the 850.
I imagine it is similar for the 920.
With that in mind, I keep the revs to about 6 k with both bikes.
I used to sometimes rev the 850 higher when after rapid acceleration. This was a mistake. It gets down the road quicker if the shifts are done no higher than 6200 rpm.
So there's no need for the high rpm or to build the engine to withstand high rpm with the stock cam as you are just revving into a lower power band, stressing the engine for no gain.

The 920 is a bit of an unknown. Jim Comstock has had to fix at least one of these by putting it back to 828 size. Iirc that problem wasn't caused by piston weight, it was due to bores going out of round. I think that can be an issue with 920s, even alloy Maney 920s. I recently ead of one of those being converted back to 828 as the 920 Maney cylinders were no longer round and causing all kinds of running issues, puking oil etc.
Time will tell with my 920, it's an experiment. At present it has loads of power and revs quickly to 6 k, at which point I shift and go again.

As I see it the stock Norton engine is sufficiently weak that any mod which moves the Rev range up is asking for trouble. That's what did the Combat in.
The 850s are a little stronger but still probably best kept to around 6k or below. The stock cam is working best here too.

If want to build a high performance Norton lookalike motor, use stronger cases , crank, lightweight pistons, TTI box etc. Don't leave any Norton in the engine at all. OK maybe the valve inspection caps!
Half way in between isn't so great if the expectation is to routinely use 7 k rpm or so.

Glen

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920 is 11% larger displacement than 828 and bigger motors tend to soften the effects of hot cams. Has anyone done dyno runs comparing the stock cam to the 2S on a 920? My guess is the 920 might see the 2S as similar or only just slightly hotter than the stock cam in an 828.