Commando Crankshaft Porn

Jim,
'A big hint is to look at the single speedway motors and they balance in the low 60s or high 50s depending on inclination of the cylinder (vertical using the higher BFs). But since a higher balance factor shakes less up and down I prefer to err that direction just a little until I learn some more and know better.'

I think there is a factor you are not considering. With speedway bikes there is a balance between slide and drive to be maintained. If the output pulsates too much you get drive. That is why the dirt speedway bikes are never twins these days, they don't get enough drive off the start and down the straights - smooth stops you from climbing the fence, however you need the balance between the two conditions to be right.. The Japanese Autorace bikes are all Suzuki 180 degree twins - very smooth running, however it is on bitumen and everything about slide and drive moves up a notch. I don't believe they ever really get drive on the bitumen. With a road race bike if the output pulses, the tyre has time to recover between each pulse, and that might be one reason that it is easier to get the rear end stepping out and cause a highside with a four cylinder bike or two stroke than an old style twin.
I think a Ducati Desmosedici MotoGP bike would be a better ride than the four cylinder jiggers. You could probably give it a lot more stick coming out of corners.

I know nothing of intelligent crank shafts so glad it baffles all of us.
Alan, informative word picture of slide vs drive. I believe part of Peel's advantage on hook up pavement or loose stuff was both the even wide pluses of 360' twin slowish rpm and the isolastics taking up the power spikes so tire could take more torque. Its the ice spiked speedways that I expect Peel to mimic w/o ice spikes of course. Canted cylinders add to balance hook up complexity. Unexpectedly I found out that slalom water skiing is very similar to motorcycle leaning with wrists straining back only steering by the tail end. Jet skis are even more so.

With my brother's speedway sidecars we only ever use trials tyres. An MX tyre will give a crash.

Yep Sir Alan slide drive is what I call 'digital traction' and there 5 ways to induce it, not counting holes or moving object impacts. Peel had to whip her crankshaft somewhat to work it out on 20/80 on/off dual purpose tires on broken pavement switch backs. Exquisite power-traction control one to one with emotional intention/muscle reflex to quantum action at the rear patch. I absolutely can not hit that level on other cycles and sense the Norton crank phenomenon have a lot to do with it. The only cycle I saw hooking up enough in crossed up slide was Kelly's 850 Norton and the only photo I can find online of another mid slide cross up wheelie into unicycle control was another of Kelly's Nortons on his own track, the rest are crashes. Ice spike speedway do this too time to time. I don't understand their engine crank placement yet expect low CoG and help front stay down in straights.

Why are there two tall nuts 23280 specified and used on Norton Commando crank ?
Is this off setting the weight of the bend tabs/nuts used on the double nutted studs?

p400 said:

Why are there two tall nuts 23280 specified and used on Norton Commando crank ?
Is this off setting the weight of the bend tabs/nuts used on the double nutted studs?

Click to expand...

I think you are going to find those same nuts on earlier twins......

As far as weight is concerned, since the cranks are (nominally) balanced......and those nuts are hollow anyway and the difference between those and shorter nuts won't be a lot...it wouldn't be a good way of dealing with weight placment.....

OBTW...your scruffy old crank needs grinding...and a new bolt set, not much like crank porn for me

SteveA said:

p400 said:

Why are there two tall nuts 23280 specified and used on Norton Commando crank ?
Is this off setting the weight of the bend tabs/nuts used on the double nutted studs?

Click to expand...

I think you are going to find those same nuts on earlier twins......As far as weight is concerned, since the cranks are (nominally) balanced......and those nuts are hollow anyway and the difference between those and shorter nuts won't be a lot...it wouldn't be a good way of dealing with weight placment.....
OBTW...your scruffy old crank needs grinding...and a new bolt set, not much like crank porn for me

Click to expand...

Yes this is just an ebay sale photo for an example, and this pictured crank looks toasty......yes every norton twin crank up thru early commandos used these two tall nuts, in this position for some reason. what is the reason for these tall nuts?

p400 said:

what is the reason for these tall nuts?

Click to expand...

Crankpin clearance and thus spanner accessability.




Tim

Tintin said:

p400 said:

what is the reason for these tall nuts?

Click to expand...

Crankpin clearance and thus spanner accessability.


Tim

Click to expand...

Could be...

It's worth noting that the studs are also longer, and the corresponding holes are to a tighter tolerance than the other four - My guess is the locating pin and these two longer studs control the location of the assembly while the other four studs just provide the remaining clamping force.
Also, longer nuts = greater threaded support = greater torque capacity.

Tintin said:

p400 said:

what is the reason for these tall nuts?

Click to expand...

Crankpin clearance and thus spanner accessability.

Tim

Click to expand...

Looking at the picture and remembering when I last had a spanner on these nuts makes that sound extremely plausible

These two tall nuts, in this outboard position were installed on thousands of Nortons!
Not shown on Plate A , but the two studs and lock plates are shown at the inboard location.
I am not finding torque gain or access reasonable, but somebody must know.
My guess was a minor balance gain, but this is probably off base as well.
Any threads on crank disassembly ? pictures of crank interior cleaning?

p400 said:

Why are there two tall nuts 23280 specified and used on Norton Commando crank ?

Click to expand...

http://www.classicbike.biz/Norton/Repai ... 0-1968.pdf

Assembling the crankshaft.........

........The two long nuts are used in the top position of the crank throw-to permit the use of a spanner.

Click to expand...

L.A.B. said:

p400 said:

Why are there two tall nuts 23280 specified and used on Norton Commando crank ?

Click to expand...

http://www.classicbike.biz/Norton/Repai ... 0-1968.pdf

Assembling the crankshaft.........
........The two long nuts are used in the top position of the crank throw-to permit the use of a spanner.

Click to expand...

Click to expand...

Excellent- I don't understand this yet - but thank you.

p400 said:

L.A.B. said:

p400 said:

Why are there two tall nuts 23280 specified and used on Norton Commando crank ?

Click to expand...

http://www.classicbike.biz/Norton/Repai ... 0-1968.pdf

Assembling the crankshaft.........
........The two long nuts are used in the top position of the crank throw-to permit the use of a spanner.

Click to expand...

Click to expand...

Excellent- I don't understand this yet - but thank you.

Click to expand...

I must admit it seems a bit of a strange explanation, as access to these is no worse (actually better - you can get a socket on them!) than the others.
I'd always assumed that as the bending moment would focus all the stresses at this point the additional threaded area was to accommodate the increased tensile forces on these studs, whereas the inboard ones would tend to be more in compression.

Perhaps not... :roll:

B+Bogus said:

I must admit it seems a bit of a strange explanation, as access to these is no worse (actually better - you can get a socket on them!) than the others.
I'd always assumed that as the bending moment would focus all the stresses at this point the additional threaded area was to accommodate the increased tensile forces on these studs, whereas the inboard ones would tend to be more in compression. Perhaps not... :roll:

Click to expand...

Right now, I feel the manual writer knew about the decreasing radius of the bolt pattern and the limited use of a tool on these nuts.......there is no added thread area, the 4 bolts are all the same length. The assembler reached inside and staked these long nuts/regular bolts.
These bolts, nuts, studs, plates are throw away...new ones purchased....long nuts replaced ?

B+Bogus said:

I must admit it seems a bit of a strange explanation, as access to these is no worse (actually better - you can get a socket on them!) than the others.

Click to expand...

Yes, it is possible to get a socket or ring spanner on them-but if they were standard height nuts then the socket or ring would probably only go about halfway onto the nut before it hit the crank radius.
The deeper nuts simply allows a greater depth of nut to be gripped by the spanner, and Mick Hemmings says this in his video-so I'm fairly sure it is the reason why those nuts are longer.

I went out and found this crank shaft, and the bolt pattern is on a decreasing radius with reference to the crank pin....meaning the outer bolts (shown with tall nuts) are much closer to the crank pin......and you run out of room for a standard nut...so you need to use tall nuts for spanner or socket access.

I am requesting an accurate weight on original Norton twin crankshafts 1965-1975. Are there threads that have accurately measured this? in grams?
searching this 50+ page thread only shows 4 posts with the word grams.
152 posts in this total with the word grams.....none with crank weights.....453.592grams per pound
why would this be an important piece of data?

10285 grams = 22.6745 lb. Would be educational to know the kinetic energy of this OD size spun to say 6000 or 7000 rpm then with different flywheel mass and OD.

p400 said:

I am requesting an accurate weight on original Norton twin crankshafts 1965-1975. Are there threads that have accurately measured this? in grams?
searching this 50+ page thread only shows 4 posts with the word grams.
152 posts in this total with the word grams.....none with crank weights.....453.592grams per pound
why would this be an important piece of data?

Click to expand...

Lets imagine that Steve Maney measured a few crank weights...then he had this to say on his web site:

MANEY LIGHTWEIGHT CRANKSHAFT
Manufactured from Aircraft quality Cr-Ni-Mo alloy billet. I can supply them in various special sizes of stroke to suit all your needs.

Special stroke sizes 93mm, 83mm, 80.4mm, 75mm, 59.6mm


WEIGHT SAVING EXAMPLES
Standard Norton crankshaft--------------------22-24 pounds
One piece billet crankshaft-------------------------28 pounds
Maney lightweight crankshaft-----------------17-18 pounds


So, his experience was a variation of up to 2lbs circa 870grams....why, well we have a production cycle and variations, but aso 750 and 850 including 850 MKIIIs of different widths...gonna vary.....what use is the data? If you knew what every individual crank weighed how would you use that data?