Commando counter balance install, why not?

So my 1972 combat has the open magneto hole still in place and that got me thinking about installing a timed counter weight in the magneto hole to smooth out the engine. Any thought of it? I wonder if it would be in the right place (can't see why not), but yet my Porsche 944 had a shaft and it worked great. Like have we all been missing this for years maybe?
Even if it only worked 50%, that would be huge.

It's not a magneto hole it was for a starter motor that the factory never fitted so the bolt spacing is different.

Zona said:

So my 1972 combat has the open magneto hole still in place and that got me thinking about installing a timed counter weight in the magneto hole to smooth out the engine. Any thought of it? I wonder if it would be in the right place (can't see why not), but yet my Porsche 944 had a shaft and it worked great. Like have we all been missing this for years maybe?
Even if it only worked 50%, that would be huge.

Click to expand...

By all means, do it as an engineering exercise if that floats yer boat.

But in all practicality, there is simply no need. With the crank dynamically balanced and the correct isolastics installed and set correctly, a Commando is already plenty smooth enough.

If you want smoother… fit JS pistons and rods, they definitely reduce vibes.

Zona said:

So my 1972 combat has the open magneto hole still in place and that got me thinking about installing a timed counter weight in the magneto hole to smooth out the engine. Any thought of it? I wonder if it would be in the right place (can't see why not), but yet my Porsche 944 had a shaft and it worked great. Like have we all been missing this for years maybe?
Even if it only worked 50%, that would be huge.

Click to expand...

Can't imagine what it would fix on a Commando. Also, that starter hole was phased out in 72 (if I remember right).

Zona said:

So my 1972 combat has the open magneto hole still in place and that got me thinking about installing a timed counter weight in the magneto hole to smooth out the engine. Any thought of it? I wonder if it would be in the right place (can't see why not), but yet my Porsche 944 had a shaft and it worked great. Like have we all been missing this for years maybe?
Even if it only worked 50%, that would be huge.

Click to expand...

This is weird because I am already working on that exact Idea. I purchased a counterbalancer for a single and it almost fit (replace gear with sprocket). Next try will be a counterbalancer similar to the 360 degree firing Triumph thruxton (replace the gear with a sprocket). It should also work on 850s with some mounting and shaft holes drilled in the timing case. The 850 cases should be fine but 750s will need some re-enforcment to take the strain. I have a solid frame Atlas I can try it on. Its gonna take some time but if it happens everything is going to be smooth. I've already made some plans so if you have the means to get started on this project - get in touch through my jsmotorsport.com website.

Honda single counterbalancer with removable gear.


Triumph thruxton counterbalancer with removable gear.

Zona said:

So my 1972 combat has the open magneto hole still in place and that got me thinking about installing a timed counter weight in the magneto hole to smooth out the engine. Any thought of it? I wonder if it would be in the right place (can't see why not), but yet my Porsche 944 had a shaft and it worked great.

Click to expand...

I see two obstacles:
* The chain drive employed by NV was too weak (was it a magneto/cb chain?). so if a chain drive is permissible, the idler gear and sprocket off the Atlas engine will have to be uprated. There are several geometric constraints .....
* The balancer shaft will be quite heavy and needs to be supported at each end. This requires the crankcase to be extended to ensure alignment. I doubt crankcase half is stiff enough to provide bearing support at the timing side.

There are other challenges too, like lubrication of bearings.

Does the 944 feature a balancer driven by chain?

- Knut

Sort out the isolastics and then no need for a balancer shaft.

My brother was a mechanical engineer, and he worked up a balance shaft set up for a Commando as an exercise. He wanted a smoother engine for an Atlas frame. Don't know what ever happened to the math and drawings.

Its doable. Lubrication is not a problem as I had problems keeping oil from getting into my magneto (now solved). Chain strength shouldn't be a problem because there are no heavy spring loads on the magneto (or balancer) like there is on the camshaft - the balancer just spins. You need a 9 tooth sprocket on the balancer. You would have to determine if a thinner chain is just as strong as a wider chain if you use a Commando cam sprocket combination with an Atlas magneto sprocket (the links and pins are the same?) or you may have to put the ignition on the crank and use the Atlas cam sprocket (this is where things get hairy). Or you would need a timing pinion gear with changed sprocket thickness..

Mounting for the balancer would depend on the engine plates on one side and the timing case on the other - but 750s would need a support bracket because the magneto timing case is machined thinner and weaker for the mag.

It would allow long distance Norton cruising with solid frames. If you have a Commando you could toss your isolastics and pour in a hard rubber compound for better handling.

I think you want 50% of the reciprical weight on the balancer shaft and you need a weight on each end to clear the center high point of the cases. Vibration should be reduced by 75%. Add the lightweight pistons and longer rods and you would be silky smooth.

Read this excellent article and pay attentiong to counterbalancers for singles and 360 deg vertical twins.

https://www.cycleworld.com/story/blogs/ask-kevin/motorcycle-engine-design-and-vibration/

Re-engineering "Jake" - the experimental balancing devise engineered by Doug Hele - seems like a better and certainly "cleaner" concept. It adds a dummy piston, rod and cylinder to the crankshaft, similar to the concept Rotax employed later on, and which is in my modern bike.

- Knut

Zona said:

So my 1972 combat has the open magneto hole still in place and that got me thinking about installing a timed counter weight in the magneto hole to smooth out the engine. Any thought of it? I wonder if it would be in the right place (can't see why not), but yet my Porsche 944 had a shaft and it worked great. Like have we all been missing this for years maybe?
Even if it only worked 50%, that would be huge.

Click to expand...

The whole point of commando isolastics is to reduce vibration to an acceptable level
Which is does rather well
Just how smooth do you want it to run?
And at what revs?

mdt-son said:

Re-engineering "Jake" - the experimental balancing devise engineered by Doug Hele - seems like a better and certainly "cleaner" concept. It adds a dummy piston, rod and cylinder to the crankshaft, similar to the concept Rotax employed later on, and which is in my modern bike.

- Knut

Click to expand...

Ducati tried the dummy piston when they first came out with their experimental single cyl monoshock roadracer and it had too much friction and robbed too much HP even when they ran it sloppy loose. The problem was solved with a conrod and a perpendicular link at the top of the dummy con rod to eliminate the dummy piston. You would also have to design the crank case and add a connecting rod - good luck with that. You need a drop in bolt on kit for customers to make this go.

Well my 850 motor with the balanced crank runs pretty smooth in my hard mounted Featherbed frame, can ride it all day and has dome many long distant rides on it in the 44+ years I built it, nothing falls off it from vibrations, don't get any tingles in the hands from the handlebars vibrating, the stock balance factor was just too low on a stock Commando motor in my opinion from the factory, or maybe I just have a freak Norton, I see Norton Commando's shake more than my hard mounted 850, back in 1981 when I got my crank balanced by an old engineering British gentleman who built formular 3 racing car chassis who knew the right balance factor for a Commando motor for hard mount set up, he rattled off all the figures that just went over my head, told me what to bring with my crank and I let him go.
Back then he charged me $49 to balance my crank, pistons, rods, pins and slipper bearing, what ever he did my motor runs pretty smooth, without spend a bucket full of money and 44 + years running in my Featherbed frame with over 140k miles on this set up, it was my everyday ride for most of its life and for many years my only transport.
My 850 motor isn't stock has had the stock cam built up to 2S cam grind, head has been shaved and ported with open exhaust pipes with cocktail shaker mufflers with very little baffles + a few other things done to the motor for reliability and smooth running, but I built my hot 850 Featherbed on a cheap budget at the time, money was tight but what I done seems to have worked very well, if I had the money I would love to throw all of Jim's light weight stuff he sells for our Commando motors as well with the balanced crank, but till I win lotto its just a dream for me.
But lucky for me I had some great old school engineers who knew their stuff back in the day, Ivan Tighe famous cam builder in Australia back in the day who did my cam grind who also put me on to the crank balancer who had a shop just down the road from Ivan Tighe, they be both long gone now, I built my hotrod before the internet came along, things are so much easier these days and what we can get for out old bikes and the last 15 years I done a lot of major upgrades to my old Norton when the kid were grown up and I owned everything I had spare money to spend on upgrades, but my motor/gearbox and primary is still the same as I built it back in the early 80s.

Vibration is not always a bad thing …

Two counter-rotating balance shafts are needed , but what exactly is the vibration problem with the Commando? I always thought it was fantastic, despite the cost cutting and continuous maintenance required.

hybridracer said:

Two counter-rotating balance shafts are needed , but what exactly is the vibration problem with the Commando? I always thought it was fantastic, despite the cost cutting and continuous maintenance required.

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The single cylinder race bikes only use use one counterbalancer and the vertical twin shakes the same way as a single. I think one would be fine. Maybe not as perfect as two but should still be enough.

A ride on a modern counter balanced Triumph will show you just how smooth a vertical twin can be (no need for isolastics).

jseng1 said:

Its doable. Lubrication is not a problem as I had problems keeping oil from getting into my magneto (now solved). Chain strength shouldn't be a problem because there are no heavy spring loads on the magneto (or balancer) like there is on the camshaft - the balancer just spins. You need a 9 tooth sprocket on the balancer. You would have to determine if a thinner chain is just as strong as a wider chain if you use a Commando cam sprocket combination with an Atlas magneto sprocket (the links and pins are the same?) or you may have to put the ignition on the crank and use the Atlas cam sprocket (this is where things get hairy). Or you would need a timing pinion gear with changed sprocket thickness..

Mounting for the balancer would depend on the engine plates on one side and the timing case on the other - but 750s would need a support bracket because the magneto timing case is machined thinner and weaker for the mag.

It would allow long distance Norton cruising with solid frames. If you have a Commando you could toss your isolastics and pour in a hard rubber compound for better handling.

I think you want 50% of the reciprical weight on the balancer shaft and you need a weight on each end to clear the center high point of the cases. Vibration should be reduced by 75%. Add the lightweight pistons and longer rods and you would be silky smooth.

Read this excellent article and pay attentiong to counterbalancers for singles and 360 deg vertical twins.

https://www.cycleworld.com/story/blogs/ask-kevin/motorcycle-engine-design-and-vibration/

Click to expand...

What you THINK you know about chain driving a balance shaft on a parallel twin bike engine, has a bit more to it.
Let me know if you care to discuss it in depth.
I've had two, thoroughly rebuilt one.

Go ahead and do it! The positive in that path is that you'll be certain of the outcome - abject failure.
Two significant reasons come to mind:
1. Consider the mass of the reciprocating parts and then the very limited space/diameter you have to work with in that location - not going to work!
2. The casing there was not designed to take the forces imposed by an effective balancer - that will fail.

I'm not saying you could not design an effective balance shaft for the Commando engine, but why? Because it's there?
The engine in isolastics is already a very capable unit and very nice to ride.

Go your hardest!
Cheers

If you did , youd introduce another imbalance , as its stuck out there , unless it was IN THE MIDDLE .

MINIMUM COMPONENT COUNT was a virtue .

A foid 2 litre V4 , with derbig 8 1/2 inch clutch , post 1970 , is Big Port .
Throwing OUT the Balance Shaft . ( & blocking oilways not reqd . )
is way better than lightening the flywheel . With 1 3/4 headers & dual system ,
it'll better 'n a Std big valve Lotus . & tow trucks out of ditches etc . If anyone has one .

the nice ' cantering ' " oscillation " introduced is better than the non existant seconday ' buzz ' they say you cant discern .

Im thinking this modern rubbish would be better WITH Iso , and electyro damping variabilty . Vicous Via Valve ? .
Most ' thumping ' on a Commando - is Road Shock through the front end . try putting your boot heel on the chaincase or timing cover - usualy they seem SMOOTH there too .

dynamo 500s had a useful place for a second balance shaft, after fitting an alternator and crank ignition trigger….