commando balance shafts?

Other than the "three cylinder" where a third none-actice pot is grafted on the front ...as any other attempt to produce a balance shaft engine been made?
Yes i know a couple of rubber washers do the trick..but rather than isolating the vibes..can they be elimanted at source?

john robert bould said:

Other than the "three cylinder" where a third none-actice pot is grafted on the front ...as any other attempt to produce a balance shaft engine been made?
Yes i know a couple of rubber washers do the trick..but rather than isolating the vibes..can they be elimanted at source?

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Many inline fours have used balance shafts.

I think what John means is, have any attempts been made to build a Commando twin with balance shafts......

Well.....do go and look at the Cosworth that was supposed to replace it.....I think you will find a couple....

As for other designs with balance shafts, yes of course....lots....though if we restrict ourselves we will probably come down to Yamaha TX750 and 500 twins that were developed in the 70s, and were mentioned recently on 'other' threads here....

(with different nomenclature outside the US)

Thats right Steve, Norton Commando engine with balance shafts, or shaft?
Surely some one as "had a go" .

Two pistons going up an down next to each other is going to vibrate an the more power you try to get out of such a set up the more it will shake.
If you fit any kind of mechanical balancing it will take power from the engine. So rubber mounting the motor costs no power an hopefully does the job.

john robert bould said:

Other than the "three cylinder" where a third none-actice pot is grafted on the front ...as any other attempt to produce a balance shaft engine been made?
Yes i know a couple of rubber washers do the trick..but rather than isolating the vibes..can they be elimanted at source?

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The most obvious, cheapest and effective way is to reduce the vibes at the source (as you suggested). The JS lightweight pistons are about 1/3 lighter than stock. The longer JS rod also reduces vibration.

Reciprocating weight compared to stock is:
112 gram savings for 750s (save another 40 grams with the Ultralight option)
200 gram savings for 850s
(for comparison - a stock pin is about 70 grams - imagine removing the approx weight of two wrist pins)

See the new Ultralight info at:
http://www.jsmotorsport.com/technical_ultralight.asp

See the balance info at:
http://www.jsmotorsport.com/technical_balance.asp

I thought vibration robbed power, un-balance a Gyro and it soon stops? Vibration is the suddern stop/ start of a mass.. causing a stress that snaps things..like Commando cranks? I smiled at a you tube video, a guy chucked a brick into a spin drier, not long before the un-balance destroyed it :!:

toppy said:

Two pistons going up an down next to each other is going to vibrate an the more power you try to get out of such a set up the more it will shake.
If you fit any kind of mechanical balancing it will take power from the engine. So rubber mounting the motor costs no power an hopefully does the job.

Click to expand...

john robert bould said:

I thought vibration robbed power, un-balance a Gyro and it soon stops? Vibration is the suddern stop/ start of a mass.. causing a stress that snaps things..like Commando cranks? I smiled at a you tube video, a guy chucked a brick into a spin drier, not long before the un-balance destroyed it :!:

toppy said:

Two pistons going up an down next to each other is going to vibrate an the more power you try to get out of such a set up the more it will shake.
If you fit any kind of mechanical balancing it will take power from the engine. So rubber mounting the motor costs no power an hopefully does the job.

Click to expand...

Click to expand...

Of course vibration robs power. The stresses heat up and wear on the bearings - and can break the crank and cases. The shorter the rod - the more vibration and the lower the RPM redline.

What is the minimum mileage expected with these pistons given the low return on the stock bore and piston

john robert bould said:

a guy chucked a brick into a spin drier, not long before the un-balance destroyed it :!:

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Automotive engines with essentially unbalanced cranks simply run stronger main bearings to cope with the imbalance.
If Commando engines used a more balanced crank, the main bearings could be a fraction of the load carrying capacity.

P.S. I can't offhand think of too many inline fours with a balance shaft ?
Fours have a fair amount of inbuilt balance, ignoring rocking couples.
Its usually singles, twins and triples that may benefit from balance shaft(s). ?
It does rob (a little) power to run those shafts.

toppy said:

Two pistons going up an down next to each other is going to vibrate an the more power you try to get out of such a set up the more it will shake.
If you fit any kind of mechanical balancing it will take power from the engine. So rubber mounting the motor costs no power an hopefully does the job.

Click to expand...

Years ago we used to rubber mount the engines in two strokes - they always seemed slower. It might have been because vibration gives you more thrill.

If you fit balance shafts to motors it might stop numbness, however it doesn't change what the crankshaft is doing to cases and main bearings at high revs. My 850 is extremely smooth at 7,000 revs, and it is very easy to over rev it. When it is idling it actually rocks backwards and forwards. What is more important ?

A well balanced crankshaft is probably the best solution to vibration. My MK111 smooths out above 2500 rpm and I can run 6 thou clearances for excellent handling.

Johno

Indeed Aco - balance shafts and rubber donuts do NOTHING towards giving the mechanical parts an easier life.
The main bearings and cases still have to be strong enough to hang together, no matter what...

But then the balance factor is all about the rider too, not forgetting that bearing loads are least at 53 % BF.
But a couple of ounces either way then doesn't make a huge difference to anything, when the whole crank is already about a pound out of balance....

Turning the balance shaft uses power was my point an it has be long acknowledged an well documented that Norton built the Commando as a stop gap model using whatever it had and the company was in its last days with no money to spare.
The best answer is to fit lighter parts that have been made since as has been said.
As to 4 cylinder engines with balance shafts I had a GPz900r smooth as silk 100bhp a lovely bike but now I prefer my commando so vibration can sometimes add to the pleasure :lol:

Time Warp said:

What is the minimum mileage expected with these pistons ...

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First of all you have to realize that because the rods are longer with the lightweight pistons the side loads of the piston skirt on the bore are reduced. I have 15,000 miles on my personal bike so far with lightweight pistons and I haven't noticed any difference since new.

See the leakdown test at:
http://youtu.be/rzp1nEGWLBk

I don't know of anyone who has needed to replace lightweight pistons on a street bike (since they were available in 2009). Some racers have had bore wear after 2 or 3 seasons hard racing but I consider that to be better than Hepolite stock pistons because Hepolite pistons would not even make it through one year back when I was racing them due to the RPMs I was putting them through (the Hepolite ring lands would pound out and the top rings would break - ruining the bore). I know of other racers who had their bores wear out quickly with stock pistons or other brands of aftermarket pistons - its all about the RPM you put them through. This is why the Norton factory had to harden the bores of their racing shortstrokes. You can get more RPM and HP with the lightweight pistons on a racebike and that is going to take its toll because anytime you demand more RPM and HP from a motor you have consequences (were talking 8000RPM+). Drive it the same as you would a stock street bike and you can expect the same mileage with the lightweight pistons.

Used piston shown below (note that the head gasket was misaligned and rubbed the piston on one side near the top).

Mmmm, there are a lot of balancer shafts out there when you go exploring.
Porsches and all sorts of things have them.
Including a PAIR of balancers shafts on new Triumph Twins.
At 1600cc, waddya expect....

about 5 days ago I had the exact same thoughts, the firs issues that came to mind were
(1) how to calculate weight and timing of the shaft
(2) the shaft wouldnt nee to be internal, it could be externally driven and covered
back in the early 70's a friend of mine bought a TX750 and for some reason he pulled it to bits , then I get the call to reassemble, I figured the power robbing balance shaft wasnt necessary and left it out, didnt seem to have any noticeable difference in vibration,

This thread has gone from the imaginary possible balance shafts while putting down the only way attempted to retain most of the engine case shapes to a tested practical lightness way then back to why balance shafts are a drag if not needed in our rubber wonders. Only reason this subject keeps coming up is due to the handling issues that onset if un-tamed rubber mounted and solid mounts hurts too much with factory oscillators. There's another way to skin this cat while retaining rubber isolation that disappears sense of machine under you plus assisting handling like all get out. Combined should be seductively fine. Some claim their Commandos never ever surprise them so they can ignore those that do run into the imfamous Cdo upsets to seek something better w/o noticing the engine vibes. I'm pleased with my plain ole Combat but its not full isolation like Peel was even with normal slugs installed. I do run about half the rubber contact area of supplied cushions though so maybe I'm a spoiled cheater.

Rohan said:

Indeed Aco - balance shafts and rubber donuts do NOTHING towards giving the mechanical parts an easier life.
The main bearings and cases still have to be strong enough to hang together, no matter what...

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I agree isolating the rider from vibration using rubber means the out of balance forces still exist and therefore components need to strong enough to cope with the stresses, but balance shafts cancel out the vibrations and therefore reduce stress.