Why ball bearing mains?

hobot said:

just speculating with assumption

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Confirmed and understood.

hobot said:

Dilemma ? * is it better to allow crank to flex by thin case sides and ball bearings or prevent it from flexing by thicker case and longer bearings?

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You are kidding yourself when you talk about "prevent it from flexing" in the context of a Norton big twin even with the best of after market cases as there is virtually nothing in it's way to stop it. Yes, you can somewhat constrain flex if placed in great heavy steel or cast iron cases with heavy reinforced bearing bosses and maybe double or even triple rows of bearings on each side.

For the Nortons, all you can do (from a practical standpoint) is design around how best to accomodate it. This is truely a case of the Ying or the Yang. If the cycling and stresses are not too great on all components involved, you have durability and everything is cool. The rollers have a design allowance to accomodate (not constrain) misalignment due to flex.

I will have to take your experienced word that normal barrel rollers such as "SuperDuperBlends" can tolerate more shaft flex misalignment than ball bearing. I must be yetconfused by those builders claiming ball bearing allowed more flex and rpm tolerance in Norton. You don't have to convince me Nortons become elastic cartoon characters with flapping seams, bobbing fasteners with a jump rope inside.

I believe there is a way around a regular crankshaft to remove all shaft flex leaving only the torque twist to tolerance no matter the rpm. But that will be another life time if Peel power aint' enough in the long run.

Oh yeah here's the Combat Bomb factors to review for bearing relevance.
All the errors and warranted work put Norton so behind it never really caught back up. Educational on how one thing leads to another and another. To me the Cream of Norton just missing a horse shoe nail here and there...
crop, once upgraded a good bit.
http://i283.photobucket.com/albums/kk31 ... ph0003.jpg
http://i283.photobucket.com/albums/kk31 ... ph0004.jpg

Laverda's have out rigger bearings to support the drive shaft, are Commados subjected to drive shaft bending when the drive is taken up?

If primary chain or belt get too tight when heated then for sure can bend crank or tranny shafts. The chain or belt torque tug on crank would also add bending flex besides the piston jerk down jump roping.

acotrel said:

With my Seeley, the choice of balance factor was easy. It is intended for racing with revs between 3,000 and 7.500. It literally shakes at 3,000 and is extremely smooth at 7,000. If you rev a 53% BF standard commando crank at 7,000, I suggest you are looking for trouble. The crank would be well out away from ideal balance and every part of the centre of it would be stretching. The loads due to out of balance at high revs must be much higher than if it occurs at low revs - simple laws of physics. I think if I had a road bike, I would use a BF at about 65 to 70% and tolerate the shake, when I was riding in slow traffic.. The Norton Atlas would have been around that figure.

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Perhaps it is worth pointing out again again again that balance factor in engines is not some magical number that gives the engine a perfect mechanical balance, and stops flywheels stretching, flexing, etc..
Its about giving the RIDER a comfortable ride.

You are never going to perfectly balance 2 pounds of reciprocating pistons with a flywheel that is 2 pounds out of balance. You are never going to perfectly balance 2 pounds of reciprocating pistons with a perfectly balanced flywheel. Thats a 100% Balance factor and a 0 Zero % balance factor, respectively, in case anyone was wondering.
At zero % balance, the whole of the out-of-balance forces are transmitted to the bicycle in the up-and-down plane.
At 100% balance, they are entirely going to the fore-and-aft plane.
Finding somewhere in between that gives the RIDER THE LEAST UNCOMFORTABLE SHAKING is what Balance Factor is ALL about...

P.S. The difference between a 52% BF and a 62 % BF is what, a few ounces. And a 72 % is a few ounces more.
On a flywheel that is a pound (16 ozs), or more, out-of-balance - deliberately, to partly counteract those pounds of reciprocating pistons, pounding up-n-down...

PPS The Atlas used a BF of circa 82 %, hasn't it been said ?
That would be to send the shakin mostly fore-and-aft, and keep the teeth chattering vibes to the rider out of the equation...

Just a question, why is the out of balance factor not resisited by the compression? Just think why a piston/rod etc is not conter balanced by hundreds of P.S.I in the reverse diirection...hope you understand me :roll:

'Its about giving the RIDER a comfortable ride.

That's what the isolastics and silly 53% BF were about. The bike was intended to be ridden in traffic, it will go fast but it will destroy itself. The Norton Atlas was the end of the line for high speed work, in that development.
'

You might think that comfort is what BF is about , but what it is really about is sending power through the transmission rather than absorbing it in the crank/bearings and cases, and shaking the bike to bits. It is like the claim that if you have a torquey motor, you don't need a close box. The theory might suggest that,but until you've tried it, you d on't really know what you are talking about. If you use a BF to suit the max revs in normal use so the motor is smooth, it will be faster. Same with rubber mounting motors in two strokes. TZ Yamahas which have rubber mounted motors lose a bit of power due to the mounts. Might stop the frame from cracking, but while they are vibrating and compressing rubber, the power doesn't go through the transmission.

JRB, if you really dig into this crank flex with piston jerks, especially on boosted applications, indeed the compression ratio makes some slight difference that improves the crank dynamics. Higher CR tends to give same effect as slightly raising BF and helps piston slow up and 'cushioned' @ TDC direction change. Boost helps relieve piston resistance too jerk down on intake too.

An isolastic Commando is a different animal than solid mounted engines, but this doesn't show up until at very limits of traction in bee lines or on tire edges. Even though slightly more power can be transmitted by more solid mounts, that ain't necessarily a good thing for tire grip if the power pulses break tire loose instead of being slightly absorbed/dampened. The un-tammed isolastics are very dangerous to play racer games on, but Peel has left the ordinary handling far behind mainly due to the genius of the isloastics, once tri linked to take out the Commando rebounding into forks tank slapping Hinging, but not so rigidly linked it becomes as corner crippled as the solids transmitting every little power pulse into tire spikes and frame kick backs that let go too easy and unpredictable even for world elite racers. My amazement was Peel being able to match the cornering G forces of my SV650 and Ninja on race tires, but nothing upsetting happening like those so 'capable' ridig moderns, then the adrenalized temptation to see what happens when trying to break free as I so easy could on the moderns, and nothing happened but even faster around counter steering than the balloon tire bikes, then I really gave her the gun and nothing upsetting happened but to turn the pavement into same freedom as THE Gravel Travel to find 3 more faster ways to steer w/o letting off. There are no authorities that have covered these extra 3 phases of cycle behavior, so its impossible to relate to others only experienced with first two energy handling phases. Each phase change, like ice to water requires different steering and power use, same as going from parking lot speed to traffic passing speed.

Rest of the world is stuck in compromises of vibration vs frame and pilot and tire tolerance but not Peel which was torquey enough not to need to shift much compared to the fast peddling needed by the 6 speeders. Peel made me loose respect for the balloon tire buzz bombs as only bee line wonders to run circles around in w/o any athletics involved but bar grip and seat planting not to be left behind by her eagerness. With a magic motorcycle like Peel, tire harmonics and power pulses become more important factors than frame or pilot tolerance for getting around gooder. I can take the bad attitudes I get from Nortoneers and modern sports bikes because I have already tested Peel in all conditions and just need MO power to go in and out harsher and smoother than any one can relate to yet.

We need to hear from Paul Smith on what bearings Sir Eddie installed for 11,000 rpm land speeder.

acotrel said:

'Its about giving the RIDER a comfortable ride.

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Yes true, but a compromise had to be made with the solid mounts, thus higher BFs.

acotrel said:

That's what the isolastics and silly 53% BF were about. The bike was intended to be ridden in traffic, it will go fast but it will destroy itself. The Norton Atlas was the end of the line for high speed work, in that development.

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Not so. Having raced isolastic Commandos with various BFs, it is not so. The isolastics make a BF selection for comfort somewhat uneccessary. The utmost smoothest race bike I have ever riddden was highly built by Herb Becker Commando near identical to Doug McRea's racer. It was smoother than most modern bikes; unbelievably smooth; smoother than any Commando or Featherbed I had ever ridden and/or raced. And what BF did Herb use - 52%. This bit about higher BF is a relic of the solid engine mount big twin days.

And to say the ATLAS engine ended its production run as a higher refined race bike engine than the Commando is utterly silly; it was more of a continuum. Remember the Combat Commando? That bike (Isolastic) would run circles around most bikes of the day. Granted later Commandos were built more for comfort but "still" stayed with the 52% BF

acotrel said:

You might think that comfort is what BF is about , but what it is really about is sending power through the transmission rather than absorbing it in the crank/bearings and cases, and shaking the bike to bits. It is like the claim that if you have a torquey motor, you don't need a close box. The theory might suggest that,but until you've tried it, you d on't really know what you are talking about. If you use a BF to suit the max revs in normal use so the motor is smooth, it will be faster. Same with rubber mounting motors in two strokes. TZ Yamahas which have rubber mounted motors lose a bit of power due to the mounts. Might stop the frame from cracking, but while they are vibrating and compressing rubber, the power doesn't go through the transmission.

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Well losses to the rubber mounts are truely trivial as they are elastic (springs) and what you put in does mostly come out. Vibration energy truely lost to the rubber mounts would have to relinquish heat to be a true loss and I have never witnessed a ISO or TZ rubber mount melting due to vibration. It just does not happen. If your theory were correct then the Commando PR racers and rubber mounted TZ'z would have had a distinct disadvantage in their day and they did not.

As for the selection of BF for the Norton big twin and similar 360 degree twins, this was all nicely outlined in another thread. The hierarchy is:

1.) Does the BF cause unacceptable vibration comfort to the rider for the intended use?
2.) Does the BF break the frame or other components?
3.) Does the BF minimize the internal stresses in the engine?

Items one and two always take precedence over item 3; thus item 3 is usually compromised.
The isolastic system more or less obviated items 1 an 2 above thus leaving the designers to optimize item 3.

Rohan said:

acotrel said:

With my Seeley, the choice of balance factor was easy. It is intended for racing with revs between 3,000 and 7.500. It literally shakes at 3,000 and is extremely smooth at 7,000. If you rev a 53% BF standard commando crank at 7,000, I suggest you are looking for trouble. The crank would be well out away from ideal balance and every part of the centre of it would be stretching. The loads due to out of balance at high revs must be much higher than if it occurs at low revs - simple laws of physics. I think if I had a road bike, I would use a BF at about 65 to 70% and tolerate the shake, when I was riding in slow traffic.. The Norton Atlas would have been around that figure.

Click to expand...

Perhaps it is worth pointing out again again again that balance factor in engines is not some magical number that gives the engine a perfect mechanical balance, and stops flywheels stretching, flexing, etc..
Its about giving the RIDER a comfortable ride.

You are never going to perfectly balance 2 pounds of reciprocating pistons with a flywheel that is 2 pounds out of balance. You are never going to perfectly balance 2 pounds of reciprocating pistons with a perfectly balanced flywheel. Thats a 100% Balance factor and a 0 Zero % balance factor, respectively, in case anyone was wondering.
At zero % balance, the whole of the out-of-balance forces are transmitted to the bicycle in the up-and-down plane.
At 100% balance, they are entirely going to the fore-and-aft plane.
Finding somewhere in between that gives the RIDER THE LEAST UNCOMFORTABLE SHAKING is what Balance Factor is ALL about...

P.S. The difference between a 52% BF and a 62 % BF is what, a few ounces. And a 72 % is a few ounces more.
On a flywheel that is a pound (16 ozs), or more, out-of-balance - deliberately, to partly counteract those pounds of reciprocating pistons, pounding up-n-down...

PPS The Atlas used a BF of circa 82 %, hasn't it been said ?
That would be to send the shakin mostly fore-and-aft, and keep the teeth chattering vibes to the rider out of the equation...

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@Rohan - Agreed the BF in a 360 vertical twin will not achieve some perfect balance and that selection is primarily driven by comfort (when necessary - the Atlas had to use it) thus a less than optimum BF is selected, the crankshaft and engine internals must be designed to take it.

Taking off on your numbers above regarding "a few ounces", let's take the scenario where selecting a 72% BF when a 52% BF would work fine. Those few out of balances ounces (say 4 ounces or 0.25lbs) yield nearly 20,000 lbs (10 tons) additional centripetal forces at 7,000 rpm. If you miss a shift and have an excursion to say 8,000 rpm that yields nearly 26,000 lbs (13 tons). These are all in addition to the other out of balance mass necessary, so the overall forces get rather huge - (forget about compression, combustion pressures etc for now). And all this is happening below you while you are sitting with your legs spread out on the footpegs.

Of course a Norton crankshaft can usually take it because many of us have done just that; probably numerous times. In my mined it comes down to minimizing the magnitude across the load reversals of the crankshaft and that can only be illustrated through bending moment analysis which is way beyond this thread and somewhat off topic.

Getting all this wrong can make the diference between 3.3 million cycles of a component before expected failure and 330 million cycles of a component before expected failure.

This is why lightening reciprocating mass is one very important factor to upping durability and reliability. A big selling point on the JSMotorsports pistons and rods. Regardless of what BF you believe you need, with lighter reciprocating mass the overall unbalanced static and dynamic loads will be less. This allows longer component life and/or higher rpm before failure.

I've used lighter pistons in a Triumph 650 engine. The first thing that you notice is that the motor spins up quicker, which you would expect considering the accelerations and decelerations the pistons and rods receive on every single stroke. The other thing which changes is the BF, so the smooth running rev range is slightly different. A friend and myself raced Triumph twins for more than 12 years . I had the 63mm short stroke 500, he had the 82mm stroke 650. He has always used BF around 79%, mine was similar. You choose what revs you want to use. His 650 was set up to pull, and was never revved over 6,300 rpm. In our local historic racing, nearly every other Triumph twin has blown up due to bottom end problems. His bike has won plenty of races.
About isolastics, - In the days when we used T1 compound Triangular Dunlops, manx nortons had Silentbloc bearings on the swing arm pivot. If you replaced them with solid bronze bushes , the bike felt better, and you needed that with those crappy tyres . Preunit Triumph twins and Matchless road going singles had a swing arm supported on a single down tube in those days - never handled due to the hinge in the middle of the frame. The whole design of the featherbed frame, the BSA frame, (and the Seeley frame) was about stopping the swing arm from moving independendently in relation to the steering head, except in the vertical direction. Yet we have commandos with the whole engine gearbox and swing arm moving indendently of the steering head and the swing arm supported inboard on two skinny plates ?
You do it your way, and I will do it mine.

acotrel said:

I've used lighter pistons in a Triumph 650 engine. The first thing that you notice is that the motor spins up quicker, which you would expect considering the accelerations and decelerations the pistons and rods receive on every single stroke. The other thing which changes is the BF, so the smooth running rev range is slightly different. A friend and myself raced Triumph twins for more than 12 years . I had the 63mm short stroke 500, he had the 82mm stroke 650. He has always used BF around 79%, mine was similar. You choose what revs you want to use. His 650 was set up to pull, and was never revved over 6,300 rpm. In our local historic racing, nearly every other Triumph twin has blown up due to bottom end problems. His bike has won plenty of races.
About isolastics, - In the days when we used T1 compound Triangular Dunlops, manx nortons had Silentbloc bearings on the swing arm pivot. If you replaced them with solid bronze bushes , the bike felt better, and you needed that with those crappy tyres . Preunit Triumph twins and Matchless road going singles had a swing arm supported on a single down tube in those days - never handled due to the hinge in the middle of the frame. Yet we have commandos with the whole engine gearbox and swing arm moving indendently of the steering ? The whole design of the featherbed frame was about stopping the swing arm from moving independendently in relation to the steering head, except in the vertical direction.
You do it your way, and I will do it mine.

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Yes, marked difference in the feel between a Featherbed and Commando. They both have their finer points.

As for spinning up faster due to less reciprocating mass; spot on. Also benefits from lighter rotational mass if you remove balance mass to adjustment after converting to lighter reciprocating components - it all adds up.

The rotational mass is only critical if the crankshaft is too light. I never saw a Triumph twin using the light Saint crankshaft which was quick. If you were used to ordinary Triumph twins with the heavy flywheel, and rode a Saint, they were unimpressive. The police had them here, and over the years there have been crankshafts for sale. You could always make your own flywheel, but why would you buy that crankshaft ? The crankshaft which has potential is the 75mm stroke one out of the later Thunderbird. How would you find one ? It would be good in a commando engine, if you could get the bore big enough. You could use one to make a 500cc domiracer, if there is a class for one.

john robert bould said:

Laverda's have out rigger bearings to support the drive shaft, are Commandos subjected to drive shaft bending when the drive is taken up?

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John,

Many competition Commandos have an outrigger bearing behind the clutch drum.......this was originally started as a works Norton practice after 5 Speed gearbox failures at almost every race meeting they entered....sure those long gearbox mainshafts flex, perhaps not pulling away from standstill but certainly when running high up in the power band, and the shaft flex misaligns main and layshaft gears until they break.....normally in a big way including bursting cases....

Better location of the layshaft, that is not relying in a bush inside the kickstart mechanism and spinning the gearbox faster with a higher primary drive ratio also helped, but the outrigger was the solution.

It is not an issue with road bikes with 4 Speed boxes and primary drives in good condition.....clearly a lot of twisting motion from the gearbox output also affects rear wheel alignment...but properly set up/maintained it is normally fine...

Or did I miss your point?

Sorry steveA i ment the crank drive shaft, yes i have seen the maney gearbox mainshaft out rigger,

The TTI gearboxes use bigger diameter main shafts, however I'm still thinking of fitting an outrigger bearing. The trouble is that the holding bolt centres and diameters are different to the standard AMC type box, so I will probably have to make the adaptation.

@acotrel - Some friendly advice. Though you can certainly use an outrigger, going to a TTIndustries box really eliminates the need so this may be your opportunity to simplify things a bit.

Not only does the TTIndustries box use a larger diameter main shaft the whole design is superior to the factory originals from the use of more roller bearings, metals used and manner in which the main and lay shafts are supported.

In some applications bearings are added on ends of the shafts and also mounted in a rigid plate so chain/belt torque don't draw shafts together stiffling some the shaft bow twisting flexure. With outrigger behind clutch so drive chain between two bearing the rigid bearing plate could be fixed to the cradle through inner case to share shaft loads all around. I think I've seen a Commando done this way as sure wouldn't want to look to Harley as a model.

acotrel said:

You do it your way, and I will do it mine.

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Words to live by. You've clearly had some success racing Triumphs and Nortons with rigidly mounted engines, so are fond of them and can't believe isolastics work well on the track. On the other hand, a number of people on this list, including me, have successfully raced (and won races) with isolastic equipped Commandos, so we know from experience that they work quite well too. I've owned and raced bikes with Commando engines in both conventional rigid mount and in isolastic mount frames, and my conclusion is that although they each definitely have their own unique feel on the track, neither one has any particular advantage in terms of lap times. The biggest advantage I see for a rigidly mounted engine in something like a Seeley frame is that it can be lighter than anything I was able to do based on a Commando frame.

It's really not necessary to prove that Commandos suck in order to claim that Seeleys and featherbeds make superb racers. It's entirely possible to accept that you can build a good race bike out of either choice.

Just my humble opinion (again).

Ken

Balanced outlook Ken and now I see acotrel may have been referring to something I had missed.

I have had the fortune (and fun) of racing various Commandos, Featherbeds and Seeley Mk2's and on any given day I would select any one of them to go on the track. They are all fun and they all have different attributes. If I am really keen on seeing any one of these bikes go faster, I select a rider better than me

The Commando is phenomenally light for a production street bike, especially when you strip down the ancillaries for racing. The design is a bit of a watershed event in the design evolution of motorcycle frames. It is not the end all and be all and there are some simple enhacements that tighten it up further. Some really fast riders on Commandos

The Featherbeds are hell for stout and a fairly progressive design for the times. Some really fast riders on Featherbeds

What caught my eye on the Seeley Mk2 frames (probably the lightest race package in their class) is that this was a seminal design for all modern bikes where there is a simple spartan triangulation from the steering head to the swing arm spindle, everything else is there to hang the ornaments off of (ex riders seat pan, rear upper shock mounts etc. ). You can really appreciate this when visualizing a silhouette of the Seeley Mk2 frame against a modern street/track rocket including the twin aluminum spar frames. Some really fast riders on Seeleys.