Crank balance factor

worntorn said:
That is interesting, when did Doug Hele do that? I know he left Norton for Triumph many years before the Commando came into existence. Did he return to Norton later on?
The other question is why would anyone bother to go to that effort when we already have (for road use) the wonderful isolastic Commando frame that sorts the vibration problem out so nicely?

Perhaps they were looking at solidly mounted race applications of the Norton parallel twin.
Click to expand...
NV(T) was desperate to extend production life of the Commando, especially after the Cosworth P86 debacle (initially Coswort was to design a DOHC cylinder head for the Commando - this plan was abandoned in 1973?), so I guess they had Dough Hele on loan from Triumph to engineer a solution to quell the engine vibrations so that NVT could abandon the Isolastic system or offer a refinement in a new post-Mk3 model. This must have happened late in 1973 or 1974 after the NVT merger.

Here is the article:
andover-norton.co.uk

Andover Norton Motorcycle Sparts Specialist - Genuine Andover Norton Commando Factory Spare Parts - Genuine Andover Norton Dominator Factory Spare Parts - Andover Norton Motorbikes

Andover Norton Genuine Spare Parts: The exclusive Source of all Genuine Norton Commando and Norton Dominator Factory Spare Parts.
andover-norton.co.uk

- Knut
 
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jseng1 said:
What we need is something to actually measure the amount of vibration and its direction at various RPMs. The closest I could come was with a polished plate attached to the motor and a sharp point to scribe the movment. I got an approx .020" oblong circle with the lightweight pistons and longer rods similar to the hand drawn image below.

Crank balance factor
Click to expand...
This is also going on inside a Norton rider's helmet when on a solid mount. Really noticeable when wearing eye glasses. When I was a kid riding my Norton it never bothered me in the least. Now it blurs my vision a little. Yippee :)
 
I'd also like to see some proof that raising or lowering the BF actually raises or lowers the vibration range. I used to believe this and tried extremes of 49% to 85% BF. I'm not so sure anymore.
 
jseng1 said:
I'd also like to see some proof that raising or lowering the BF actually raises or lowers the vibration range. I used to believe this and tried extremes of 49% to 85% BF. I'm not so sure anymore.
Click to expand...
Jim I can understand where you are coming from, maybe I was lucky with my Commando/Featherbed build back in 1980/82 finding an old English gentleman who knew his stuff and what I was building, or I just have a freak of a bike, the older British bikes will never be like a modern bike for smoothness and vibration free, I do know the difference when riding my Norton and my newer 1200 Thruxton, my Norton does have that tingle but for me it's all in the right places, my foot pegs don't vibrate, and having thick wall alloy bars made a big difference, I can see out of my right bar end mirror, the vibs aren't that bad in the high 2 rev zones it get bad but it always smooths out once over those 2 areas in the rev zone and I know the when it's going to be bad.

About 20 odd years ago I pulled up on my Norton at my local British bike shop (BJs in Brisbane) to get 2 Amal rebuild kits, my Norton is loud and they all heard it pulling up, there was a customer in the shop and he went outside and was checking my Norton out while I was being served, he waited till I came out and was asking me all about my hotrod Commando/Featherbed and asked how the vibrations where being hard mounted, I said it's not too bad then he told me his story.
He had built a Commando/Featherbed but he said it just shock him to bits and the vibrations were so bad and he couldn't ride it far, so I asked him what he had done, he threw in a stock Commando motor that wasn't built for hard mount Featherbed, just made the engine plates and threw in the stock motor, well I said straight away that's your problem and he didn't have a head stay mount and told him very important to run a strong top head stay.
I told him what I had done to my motor and gave him my phone number and I took off with a full rev out down the street, that was the last I heard from him.

I just can't understand why my Norton is so good, it's very enjoyable to ride and get it up in the tight twisties up in the ranges I have so much fun, that's where I push it to its limits of rubber on the road and the edge of my tyres, it's so good, everything works so well together.
My Norton was my first bike I ever built and learned from my mate Don's mistakes with his 750 Commando/Featherbed.

Ashley
 
jseng1 said:
What we need is something to actually measure the amount of vibration and its direction at various RPMs. The closest I could come was with a polished plate attached to the motor and a sharp point to scribe the movment. I got an approx .020" oblong circle with the lightweight pistons and longer rods similar to the hand drawn image below.

Crank balance factor
Click to expand...
What a great test. I would not thought of that.
 
ashman said:
Jim I can understand where you are coming from, maybe I was lucky with my Commando/Featherbed build back in 1980/82 finding an old English gentleman who knew his stuff and what I was building, or I just have a freak of a bike, the older British bikes will never be like a modern bike for smoothness and vibration free, I do know the difference when riding my Norton and my newer 1200 Thruxton, my Norton does have that tingle but for me it's all in the right places, my foot pegs don't vibrate, and having thick wall alloy bars made a big difference, I can see out of my right bar end mirror, the vibs aren't that bad in the high 2 rev zones it get bad but it always smooths out once over those 2 areas in the rev zone and I know the when it's going to be bad.

About 20 odd years ago I pulled up on my Norton at my local British bike shop (BJs in Brisbane) to get 2 Amal rebuild kits, my Norton is loud and they all heard it pulling up, there was a customer in the shop and he went outside and was checking my Norton out while I was being served, he waited till I came out and was asking me all about my hotrod Commando/Featherbed and asked how the vibrations where being hard mounted, I said it's not too bad then he told me his story.
He had built a Commando/Featherbed but he said it just shock him to bits and the vibrations were so bad and he couldn't ride it far, so I asked him what he had done, he threw in a stock Commando motor that wasn't built for hard mount Featherbed, just made the engine plates and threw in the stock motor, well I said straight away that's your problem and he didn't have a head stay mount and told him very important to run a strong top head stay.
I told him what I had done to my motor and gave him my phone number and I took off with a full rev out down the street, that was the last I heard from him.

I just can't understand why my Norton is so good, it's very enjoyable to ride and get it up in the tight twisties up in the ranges I have so much fun, that's where I push it to its limits of rubber on the road and the edge of my tyres, it's so good, everything works so well together.
My Norton was my first bike I ever built and learned from my mate Don's mistakes with his 750 Commando/Featherbed.

Ashley
Click to expand...
If your featherbed commando has 19 inch wheels, it should be pretty good. The Commando motor is usually heavier than a Triumph 650 motor, and I suggest a Manx always handles better than a Triton because of the position of it's centre of gravity. The centre of gravity of your bike is probably further forward than it is in a Triton. It should feel nice and positive in corners - when the bike is like that, it can be ridden faster.
 
After reading through a lot of this info I'll be maybe considering incorporating ISOs into frame
I don't know if there's enough room yet but it's only metal!
My only concern would be not having the swing arm attached to the engine/gearbox cradle the chain alignment
IE the motor trying to tear itself backwards and to the left
The chain would become slack
Could probably solve this with some links /rose joints at the expense of some vibration
The reason I moved away from triumph twins was the sheer amount of vibration I find a triumph t140 intolerable after riding a commando for example
I should be picking my new project up this week so I shall have a measure up to see if ISOs are possible
I'm also wondering if the ISOs only really work well with the swinging transmitting the vibes away through the wheel,tyre , using the road as a damper?
Anyone have any experience of running a commando on its ISOs in a different frame without the swinging arm fitted?
 
acotrel said:
If your featherbed commando has 19 inch wheels, it should be pretty good. The Commando motor is usually heavier than a Triumph 650 motor, and I suggest a Manx always handles better than a Triton because of the position of it's centre of gravity. The centre of gravity of your bike is probably further forward than it is in a Triton. It should feel nice and positive in corners - when the bike is like that, it can be ridden faster.
Click to expand...
I don't think the 650 Triumph engine is much lighter than the Commando engine.
I searched around for that number and found that 139 pounds was the most often quoted number for the unit 650 engine weight. One person weighed their engine for shipping and said it was 137, without engine plates.
Iirc my Commando 920 with transmission, alloy engine plates, isos and alloy barrel was 130. I'm guessing that a stock 650 Triumph engine with plates will be within 5 pounds of a stock Commando engine/trans with plates. I expect the Commando might be a few pounds heavier due to the isos.
Those are pounds well spent!

Glen
 
baz said:
After reading through a lot of this info I'll be maybe considering incorporating ISOs into frame
I don't know if there's enough room yet but it's only metal!
My only concern would be not having the swing arm attached to the engine/gearbox cradle the chain alignment
IE the motor trying to tear itself backwards and to the left
The chain would become slack
Could probably solve this with some links /rose joints at the expense of some vibration
The reason I moved away from triumph twins was the sheer amount of vibration I find a triumph t140 intolerable after riding a commando for example
I should be picking my new project up this week so I shall have a measure up to see if ISOs are possible
I'm also wondering if the ISOs only really work well with the swinging transmitting the vibes away through the wheel,tyre , using the road as a damper?
Anyone have any experience of running a commando on its ISOs in a different frame without the swinging arm fitted?
Click to expand...
The fellow I purchased my MK3 from sold it to finance an expensive restoration of a Triumph T140. He contacted me after the Triumph was finished and on the road to say that he was interested in repurchasing the MK3, should I ever want to sell it.
I guess the vibrations of the T140 were so intense that he didn't enjoy riding it at all.

Glen
 
marinatlas said:

The featherlastic is a solution ....;)
Click to expand...
You don't hear much about them as I say I don't think they didn't work too well or they would be everywhere, as a Featherbed frame the hard mounts and motor are all part of the frame and handling affect, solid mounting, put Isolastic into the frame would just upset the handling of a Featherbed frame and make it worst, as I have said mine is fine and handles like riding on rails, why would I stuff that up by putting rubber mounts on the main part of a Featherbed frame, its hard to explain but when I ride my Commando/Featherbed I am just the rider controlling the throttle the frame does all the work, I just point and hang on when I get into the tight twisties, sometimes I got to look back and see if I did go through that last corner, it handle so well.
acotrel said:
If your featherbed commando has 19 inch wheels, it should be pretty good. The Commando motor is usually heavier than a Triumph 650 motor, and I suggest a Manx always handles better than a Triton because of the position of it's centre of gravity. The centre of gravity of your bike is probably further forward than it is in a Triton. It should feel nice and positive in corners - when the bike is like that, it can be ridden faster.
Click to expand...
When I built my Commando/Featherbed I used as much of my Commando parts as I could including 19" wheels front and back Akront alloy rims laced to the Commando hubs and Commando frontend, I did my homework before I started the conversion to the Featherbed frame and this was before the internet, the crank balance factor was the most important part of the conversion and built my motor for the Featherbed.
My good friend Don who got me into Norton's and Featherbed frame Commandos, his 750 C/FB was the first Norton I ever rode at 17 years old but Don's motor was upright like the Domie motor, his crank was lighten and polished as well balanced but he had problems and his crank was lighten too much (in my opinion) and he also was a bit of a butcher/rough when he built things, odd size bolts and nuts, use what ever was laying around, I took notice and did things differently to how he built his, I did it right I say.

Ashley
 
worntorn said:
The fellow I purchased my MK3 from sold it to finance an expensive restoration of a Triumph T140. He contacted me after the Triumph was finished and on the road to say that he was interested in repurchasing the MK3, should I ever want to sell it.
I guess the vibrations of the T140 were so intense that he didn't enjoy riding it at all.

Glen
Click to expand...
My BSA A10 actually vibrates more than a t140 but I use it differently
I don't really thrash it through the box or ride it at high speed
Or for any real distance
It's a very different type of bike experience ( for me at least)
 
I replaced the Amal barrel style grips on the BSA with modern soft grips that were advertised to be fantastic for absorbing vibration.
I made it about a mile down the road before turning back.
By the time I got home my hands hurt like crazy!
This was riding at about 55 mph with raised gearing.
The Amal style grips went back on and now things are back to bearable.
And they say that the A10 is smooth compared to the A65!

Glen
 
worntorn said:
I replaced the Amal barrel style grips on the BSA with modern soft grips that were advertised to be fantastic for absorbing vibration.
I made it about a mile down the road before turning back.
By the time I got home my hands hurt like crazy!
This was riding at about 55 mph with raised gearing.
The Amal style grips went back on and now things are back to bearable.
And they say that the A10 is smooth compared to the A65!

Glen
Click to expand...
My oif a65 lightning was about the same as my A10
My mate has an oif thunderbolt that is a lot smoother
I was talking many years ago with Andy at FD motorcycles and he'd had a customer in with an incredibly bad vibrating BSA a50
Eventually he took the flywheel off the crank and found two sets of fixing holes
He bolted the flywheel back on to the second set of holes and the engine ran smoothly
 
Rickman and Seeley used 'Aluminium Alloy' plates. Of course the alloy of choice will have been aircraft spec varying 'numbers' based on recommendation and availability.

Not sure why a race bike would use anything else. Or why a production road bike would use anything other than mild steel!

Steve Maney favoured 78% for my race engine. I'm with FE on the acceptable range being 72 to 80% I suspect the lower number would be good for a road bike, certainly I find the higher number good for a race bike.

Dynamic Balancing? Never tried it, but there is evidence for it, as FE says.
 
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Schwany said:
Need money to burn for that set of modifications. A 2024 Ducati Scrambler or Street Fighter would be cheaper. Actually those 2 2024 Ducati models would be cheaper than what I have in my P11 paint shaker. ;)
Click to expand...
The money I have burned bringing my commando up to an early 80s average bike specs is unbelievable 🤣🤣🤣🤣
 
baz said:
After reading through a lot of this info I'll be maybe considering incorporating ISOs into frame...
Click to expand...
Instead of going to all the fabritation, trouble and extra weight of isolastics. Consider pistons that are more than 1/3 lighter than stock and longer ultralight Carrillo rods that reduce vibration even more. Vibration is reduced by 1/3 to 1/2 and you have Carrillo rods that last forever. Less cylinder friction and increased performance.
 
ashman said:
You don't hear much about them as I say I don't think they didn't work too well or they would be everywhere, as a Featherbed frame the hard mounts and motor are all part of the frame and handling affect, solid mounting, put Isolastic into the frame would just upset the handling of a Featherbed frame and make it worst, as I have said mine is fine and handles like riding on rails, why would I stuff that up by putting rubber mounts on the main part of a Featherbed frame, its hard to explain but when I ride my Commando/Featherbed I am just the rider controlling the throttle the frame does all the work, I just point and hang on when I get into the tight twisties, sometimes I got to look back and see if I did go through that last corner, it handle so well.



Ashley
Click to expand...
I agree with you, in the featherbed the engine/gearbox assembly acts as a load bearing member, stiffening up the frame. In the featherlastic that extra stiffness is lost.
 

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