Commando Crankshaft Porn

From a practical standpoint, for a Commando crankshaft, not much. Mostly it just lets you get a lighter total crankshaft weight. If you want to keep the same balance factor with a smaller OD flywheel, you will need to add some weight to the counter balance part of it. By turning down the outside, you've moved the center of mass of the counterweight closer to the centerline of the crankshaft, so to generate the same amount of centripetal force for balancing, you have to add weight to make the counterweight heavier. Stll, by turning it down, you've taken more weight off than you have to add back, so the net result is a lighter crankshaft.

Ken

Ok Ken, you described Ms Peel's crank with 1/2" less OD flywheel you have on hand, but what I more wanted to understand is how those features might play out in rpm tolerance. Seems like a good thing over all, worked great prior and stuck with it now. Maybe some of the porno photo examples are effectively smaller OD too, but can't tell just by looking. Ron of East Coast fame said was for faster reving and less rpm whip.

Well, when you turn down the flywheel and add some mass to the counterweight to keep the balance factor the same, it doesn't change the magnitude of the centripetal force, so I don't see it having any impact on the amount the crank bends at whatever rpm you're concerned with. However, the centripetal force is proportional to the radius to the center of mass, but the moment of inertia is proportional to the square of the radius, so you do see a reduction in the moment of inertia. In theory, that would affect how the crank oscillates in torsion, so it might have an effect on crankshaft fatigue. I don't think for a Commando crank the effect would be very significant, but I don't have a detailed computer simulation of a Comando engine to plug the data into and see.

The significant effect of a smaller flywheel seems to just be getting a lighter crankshaft. We've beat the subject of light vs. heavy crankshafts to death in other threads, and there's no point in me just repeating it all again in this.

Ken

page 98 / 102 - 104 in the Tim Hanna ' Legend of Burt Munro ' epistle states the old bean cut n shut a Val Page Triumph 6/1 650 crank to 45 Deg. offset .

for a Parallel V-Twin , before the war . So Irvine is incorrectly attributed with its invention .
Though some diallouge Via the Burns / Wright Record Vincent
may have occured between or to Munro & Irving.

No whingeing over a few degrees either , thanks .

Studying chopping up a Four or Six , to a twin , Useing a Six Cyl steel Nissan crank will get a 120 degree offset . For a twin cylinder triple .
If its good enough for Laverda to do a three cylinder four ( flat plane 180 deg triple crank ) why NOT .

If we want to get really awkward , We could use a 5 cyl Audi / VW crank , for a 72 degree or would it be 144 degree offset .

These Audi / Honda V 5s are disarmingly close to the Hopwood ? / Hele concept of Modular multis promolagated as concieved around 1970 .

I've heard of a local racer who has installed a 270 degree crank into his Triumph. It appears to go well. My problem with doing that to a norton is in balancing the shaft , however I believe dynamic balancing could be the answer. As I understand it the staggered crank only affects primary balance, and it seems to me to be suited more to a relatively low revving motor. It seems very difficult to calculate what masses the flywheel and bob weights should be , if you were making a billet crankshaft. I understand that Megacycle make cams for use with the staggered crank in Nortons. I would have to do a big rethink about the exhaust configuration, and how to compensate for a two into one with the timing. The thing about the staggered crank, is that it works for Ducati - the 90 degree vee gives the same effect.
Rohan - crankshaft rebalancing is not about rider comfort, it affects how the motor performs and stays together, and whether the frame cracks and the rest of the bike falls to bits .
I don't believe the staggered crank is an easy answer, however it might have saved the Norton Company in the 70s. I believe the modern Norton twin has balance shafts. That might save the bike, but the crankshaft will still be doing its antics inside the motor. The vibration is still there affecting the bit of aluminium between the main bearings and the balance shafts.

Ken,
'The significant effect of a smaller flywheel seems to just be getting a lighter crankshaft. We've beat the subject of light vs. heavy crankshafts to death in other threads, and there's no point in me just repeating it all again in this.'

The arguments about balance factor and crankshaft weight on this forum sometimes indicated a level of ignorance and inexperience. I've done a fair bit with racing motorcycles over the years, and I have also read a lot. I am a scientist, not an automotive engineer. Phil Irving obviously knew a lot more about harmonics and crankshaft balancing than I do. I don't believe he was a superman but the subject is an avenue well worth studying. For some bloody strange reason, I now believe in Norton Commandos - mine excites me. For many years I lost the urge to race, it has now returned just when I am almost broke. Pity the staggered billet crank is such an expensive exercise.

'I don't think for a Commando crank the effect would be very significant, but I don't have a detailed computer simulation of a Comando engine to plug the data into and see.
'

Perhaps you should weight the big ends of a norton crank, and spin it up in a crankshaft balancing machine and then shine a strobe light onto it as well as measure the bearing loads using a computer data gatherer ? It might be an investment in a better understanding.

acotrel said:

'I don't think for a Commando crank the effect would be very significant, but I don't have a detailed computer simulation of a Comando engine to plug the data into and see.
'

Perhaps you should weight the big ends of a norton crank, and spin it up in a crankshaft balancing machine and then shine a strobe light onto it as well as measure the bearing loads using a computer data gatherer ? It might be an investment in a better understanding.

Click to expand...

An interesting idea, but I don't think it would show you much. Most automotive balancing machines don't spin the crankshaft very fast. I think 450 to 500 rpm is typical for max rpm capability for the usual balancing machines in auto machine shops, and most balancing is done well below that. It doesn't matter what rpm the balancing machine runs the crank at, as long as it is fast enough for the machine to measure the out-of-balance condition. Once it is balanced at whatever rpm the machine uses, with a particular set of bob weights on the rod journals, it is in balance for all rpm, with those specific bob weights, and within the accuracy capability of the machine. You don't want to confuse balancing on the machine with bob weights, with what happens in the engine with real rods and pistons in motion, where you have both rotating and reciprocating forces. There are no reciprocating forces when the crank is on the balancing machine, and you end up with perfect balance for the bob weights you choose. As has been said many times, in many ways on this forum, balancing a Commando crankshaft to any particular balance factor is just a compromise, trying to find the "best" solution for a given combination of chassis and engine for a particular application (road, street, drag racing, etc.).

I agree that it would be interesting to build a setup where you could safely spin a Commando crank up to 7000 rpm or so and see how much it bends, but even that wouldn't tell you what it is doing in a real engine, where it speeds up and slows down every revolution. Actually, hobot's idea of putting a sensor in the crankcase to measure runout at the flywheel in real time sounds like the most interesting suggestion. Maybe I'll give that a try when I get my data logger built.

And maybe not. Most serious Commando racers and engine builders have figured out what works for them in terms of balance factor and crankshaft weight, and that info has been pretty freely shared here. For lightly modified street bikes, values in the vicinity of the stock balance factors seem to work just fine. Not really that much need to reinvent the wheel.

Ken

Ken while eye balling cases for jet port clearance consider where to place a tapped hole to run a witness bolt up to Peels flywheel rim. I know its lumpy now with the weld bead but so what just run bolt in to stop on high spot then back out part a turn which the thread pitch can measure. My impression of crank deflection is that it hardly bends at all till some threshold crossed to deflects enough to suddenly matter. There is something going on with sonics of tires and parts deflection cycles in our hearing range 4000~9000 hz which is also the area of crank concern.

Hartmul may have the best crank rpm solution yet, what ever BF used. We must keep in mind crank only has to stand like upper 7000's at most as we had pointed out there's not much if anything to gain power wise spinning the fairly long strokes higher d/t bore friction. Of course in lower gears that's a non issue so rev limiter is only fail safe. But where to set it?

It would be possible to build a test rig with barrels supported over the crank. And the main bearings fitted with load cells. If I was going to build a motor with a staggered crank, I would do the exercise. I cannot believe that MAP triumph achieve the optimum. The problem with doing it to a commando is that the job is twice as difficult. Cam timing is usually asymetrical, and while the shaft carries both the inlet and exhaust cams, the job of trying the alternatives is that much harder .

@comnoz

at page 6 you showed your crankshaft work, can i know why you choose cryogenic treatment instead of heat treatment?
norton cranks is using EN16 or 605M36
Tensile strength 127,343 psi
Yeild strength 100,801psi
http://www.kelvinsteels.com/spec_605m36.htm

with cryogenic how many percent improvement are you looking for?

my machining work for my 90 cranks are almost done using 4340, should i cryogenic or heat treat it?

heat tempering mostly involves solute mixing better so should be done prior to cyrogenics which finished the crystal conversion and then a slow heat treatment to ease the freeze compression stresses. Do major machine work before cryo and the fine tune and surface finish after if practical.

All the heat tre atment in the w orld won't stop a failure if you use bar stock to make the crank, and find the inclusion in the centre of it ends up where the output shaft is located. Do you guys do sulphur prints before machining ?

Has anyone here had experience with a Norton crankshaft from MAP ?

http://www.mapcycle.com/catalogsearch/r ... crankshaft

acotrel said:

All the heat tre atment in the w orld won't stop a failure if you use bar stock to make the crank, and find the inclusion in the centre of it ends up where the output shaft is located. Do you guys do sulphur prints before machining ?

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The sulfur print method is suitable for process control, research and development studies, failure analysis, and for material acceptance purposes. Steel is procured and used all the time for critical applications through certification acceptance (formal QA/QC). I suppose if you were looking at building a space shuttle you might consider it but it flys in the face of modern QA/QC; those steps are taken prior to acquisition.

acotrel said:

All the heat tre atment in the w orld won't stop a failure if you use bar stock to make the crank, and find the inclusion in the centre of it ends up where the output shaft is located.

Click to expand...

Equally true for forged or cast steel crankshafts, not just those machined from billets. Very unlikely with the quality of modern 4340 VAR steel, the most common material in the US for custom crankshafts machined from billet. If you were still concerned about flaws in the billet, you could have it x-rayed. I don't think that's common practice in the industry, but I have seen it done. I had Axtell's shop make some titanium retainers for me back in the day, and they had the bar I supplied x-rayed before they would use it.

Like DWS said, the QA/QC is done at the mill. When I bought a billet of 4340 VAR with plans to make a Norton crankshaft, all the certification paperwork came with it.

Ken

:shock:

Designed c.1899 by one of the all-time great automotive engineers, Frederick Lanchester, the 4000cc horizontally-opposed twin cylinder had dual connecting rods per cylinder and dual counter-rotating crankshafts, which were joined by bevel gearing. Just as it was designed to do, the unusual configuration provided smooth running - something that was previously considered unattainable in the early days of the internal combustion engine.



Another nearly unbelievable technical feature of the engine was an efficient and reliable cam driven, single valve per cylinder layout. It worked by way of a disc valve in the initially combined intake/exhaust manifold that opened and closed the correct upper tracts as required - it's difficult to describe with eloquence befitting of its elegant engineering.



Now we know were we went wrong . !

Before the marque's sad decline into re-badging and eventual closure in 1955, it was known as a maker of some the highest quality and most expensive cars in the world - easily the match of Rolls Royce.

Incidentally, Lanchester was the first ever British car manufacturer and is still registered as an active, non trading company.

Matt Spencer said:

Just as it was designed to do, the unusual configuration provided smooth running -...

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Hm. How? The piston forces cancel out each other, the bobweight forces cancel out each other horizontally but what about the vertical forces of the bobweights? In the end your back to square 1 with this design IMHO.


Tim

Tintin said:

Matt Spencer said:

Just as it was designed to do, the unusual configuration provided smooth running -...

Click to expand...

Hm. How? The piston forces cancel out each other, the bobweight forces cancel out each other horizontally but what about the vertical forces of the bobweights? In the end your back to square 1 with this design IMHO.


Tim

Click to expand...

The piston forces do not cancel out in the Matt Spencer illustration above. Look again, especially the middle illustration.

Both pistons have the same direction of travel.

In contrast, BMW boxer pistons travel in opposite directions, thus their forces due to acceleration & decceleration cancel.

Dances with Shrapnel said:

Both pistons have the same direction of travel.

Click to expand...

Ah, yes, off course... sorry, classic case of seeing something that I wanted to see instead of what was actually displayed.


Tim

It is good that such ideas get tossed around for peer review, collectively we might achieve something innovative.