Reverse weighted Norton crankshaft ?

Has anyone ever wondered why Norton cranks have the heavy flywheel in the middle, and the trimmed wheels on the sides. ?

What would happen if the full circle wheels were on the outsides, and the central connecting bit slimmed down to as minimal as possible ? - and still be sufficiently strong to connect it all together, obviously.

Would this give less potential flywheel flexing ?
Or would having more weight on the timing side lead to potential crank twisting problems ??
And does having the unbalanced portions nearer the bearings give smoother running... ?

Think of the crank as the famous "simply supported" beam and the worst place to put a load is in the centre, but it's probably not possible to get enough mass in the cheeks(?) of the crankshaft to provide the necessary balance factor.

There have been theories with good arguments for both ways- weight on the ends and weight in the middle. I stick with the thought that Norton got it about right. Jim

comnoz said:

There have been theories with good arguments for both ways- weight on the ends and weight in the middle. I stick with the thought that Norton got it about right. Jim

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Jim, it's time you started thinking outside the box.

Some people believe the central flywheel enhances manouvreability , or at least , that the mass ( counterweights ) spread along a
four cylider crank , through gyroscopic procession , resist / retard changes in direction of the motorcycle .

When you look back at twin port , twin carb singles , its alledged Turners speed twin was designed to resemble singles to avoid ' buyer resistance ' . The inirtia is much like a single , with the central flywheel mass . Also the twin ' Ball / roller ' bearing mains have less drag
resistance than plain / shell bearings. Specialy when there not there , at the center .

The appearance of the Norton Twin resembles a Single more than the Triumph , unless Im misstaken .

Ideally , the counterweights would be arranged to provide the minimum stressing of the crank , as the patented ! Isoastics allow for
vibration to be produced / absorbed . Rather than arranged for minimal vibration .

Percieving the flywheel / inirtia as a ' store of energy ' , if the forces are fed into / absorbed by , It The Flywheel with the intention of
utiliseing the cumulative force rather than perhaps opposing forces cancelling Ea other out , more output should result. In Theory . :lol:

The irregular rotation ( Deg. / Sec. per revolution ) ordinarilly results in the use of ' Torsional Vibration Dampers ' as utilised on
good old Chevy V8s etc . Better quality larger ones for higher outputs & rpm's .

Arrangeng the counterweights irregularly along the crankshaft could allow the loads to accumulate in a progressive manner , as in a wave ,
along the crankshaft . And eventually to the Back Wheel .

Holmeslice said:

comnoz said:

There have been theories with good arguments for both ways- weight on the ends and weight in the middle. I stick with the thought that Norton got it about right. Jim

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Jim, it's time you started thinking outside the box.

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I have- and I have the boxes full of broken parts to prove it. :?

I have- and I have the boxes full of broken parts to prove it. :?

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The road to success is paved with failure.

Rohan said:

Has anyone ever wondered why Norton cranks have the heavy flywheel in the middle, and the trimmed wheels on the sides. ?

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Simply put, if the flywheels were on the sides then you would have twice as many parts

In all seriousness, the "wheels" on the outside are not trimmed but they are "porkchop" balance weights.

Rohan said:

What would happen if the full circle wheels were on the outsides, and the central connecting bit slimmed down to as minimal as possible ? - and still be sufficiently strong to connect it all together, obviously.

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All the Norton twin needs are three porkchops for dynamic balancing; the middle mass of the fly wheel is added for improved smoothness of operation. The flywheel mass in the center also provides the maximum damping of flexural bending "whip"; if this mass were to the sides it would do nothng for damping of the flexural whip. You are somewhat limited as to how close you can pull the cylinders together so I don't know where you would go with this.

Rohan said:

Would this give less potential flywheel flexing ? Or would having more weight on the timing side lead to potential crank twisting problems ?? And does having the unbalanced portions nearer the bearings give smoother running... ?

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I don't know what you mean by "flywheel flexing" but the center flywheel (versus two flywheels to either side) will dampen flexing. I doubt the location of the flywheel (inboard or outboard) will have any noticeable effect on smoothness.

If you went with an infinitely heavy flywheel you would have the smoothest feeling Norton around.

Dances with Shrapnel said:

If you went with an infinitely heavy flywheel you would have the smoothest feeling Norton around.

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I'm pretty sure that's been mentioned before, but would probably inhibit spool up which is pretty nice at the moment.

Dave
69S

Spreading the mass out along the crank is one of the arguments I have heard for why the Honda 750-4s where harder to bring into a corner than a Commando. The Yamaha 650 cranks were built with the weight distributed along the length as well but not as dramatic as the 4 cylinder. Here are some Ebay links as to what those cranks look like.

http://www.ebay.com/itm/Yamaha-XS650-Cr ... 35b5f96195

http://www.ebay.com/itm/79-Honda-CB750K ... es&vxp=mtr

The argument made sense to me, so I have pretty much accepted it for years as valid. Now back to our experts to sort it out...

Russ

comnoz said:

Holmeslice said:

comnoz said:

There have been theories with good arguments for both ways- weight on the ends and weight in the middle. I stick with the thought that Norton got it about right. Jim

Click to expand...

Jim, it's time you started thinking outside the box.

Click to expand...

I have- and I have the boxes full of broken parts to prove it. :?

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Time to start thinking outside the boxes of broken parts!

Jim Thinks Norton got it right, Early frames snapping, gearbox's exploding, combat engines blowing up,,,etc.etc....makes me wonder if norton got anything right! except the MANX.

If you went with an infinitely heavy flywheel you would have the smoothest feeling Norton around.

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Should we anticipate any problems picking an infinitely heavy bike up off the sidestand ?

Or any gyro problems in corners ??

john robert bould said:

makes me wonder if norton got anything right! except the MANX.

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Thats a dangerous subject to bring up !
While looking and sounding wonderful, manxes were famous for the number of different ways they could DNF. Like many a race bike, right on the limit of everything...

The factory bikes, having titanium con-rods ?, and everything vulnerable replaced before each race had a better run.... ?

Interesting thoughts all, thanx.

Tuners have done this. C.R. Axtell used to do it to Triumph dirt track engines he built, and in the photo below a Norton crank built by Heinz Kegler. Axtell said it made the Triumph cranks last longer in his racing engines.

beng said:

Tuners have done this. C.R. Axtell used to do it to Triumph dirt track engines he built, and in the photo below a Norton crank built by Heinz Kegler. Axtell said it made the Triumph cranks last longer in his racing engines.

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I don't remember seeing that photo turn up in the "crank porn" thread. It would be nice to include it in that gallery as it certainly fits. Do you have any data on what it weighs or the balance factor?

Russ

Rohan said:

Would this give less potential flywheel flexing ?

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Yes, off course, but also more vibration could be felt by the driver. IMHO the bikes are actually running overcritical - meaning beyond the first resonance frequency of the crank train - at least at peak rpm and thus are actually "self-balancing" themselves to a certain extent. The crank most likely is already on its way back from the first order node by then. Very unusual by todays standards but then there is a reason that a Norton twin engine doesn't look like a BMW P-twin. The AJS/Matchless twins with middle bearing are known to shake substantially more then their Norton and Triumph counterparts.

In a Commando where the Isos take care of the vibes it would make sense to reduce the load on the mains by moving the bobweights as far out as possible. In a Featherbed race bike it would mean the rider would have to tolerate more vibes.


Tim

Tintin said:

IMHO the bikes are actually running overcritical - meaning beyond the first resonance frequency of the crank train

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By that you mean that you believe the resonant frequency of the crank is not much more than 100 Hz? such that at 6,000 rpm it would be resonating?

ggryder said:

By that you mean that you believe the resonant frequency of the crank is not much more than 100 Hz? such that at 6,000 rpm it would be resonating?

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Let me put it this way: I wouldn't be surprised if that is the case (not the crank only, the whole system). Everything on this old bikes is "soft" by modern standards: The bolt-up crank, the main bearing support in a crank case that I'd at best call flimsy compared to the ones I'm dealing with in my daily work, the imbalance of the central rotor is massive, the more or less "random axial stiffness" of the NJ bearings and so on. I have to admit that I haven't done the maths - it is just a gut feeling based on some "indicators". A relatively similar engine with a much stiffer main bearing situation is know to vibrate more and then there is the story behind the detonating Combat engines. I have also to admit that I'd find an overcritical operating point pretty strange for a crank train but that doesn't mean that it would be impossible.


Tim