Quality Billet crank

madass140 said:

I measured one years ago to see if what I had read was correct, well it wasnt barrel shaped , I would guess if there was any change in the shape it would of been that the Superblend had a bigger radius on the ends, but I couldnt guarantee that and I'm probably wrong.

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I did the same thing - the FAG Superblends just had the sharp edge ground out to a smooth curve on the ends of the rollers.

With a note that the Randsome & Marles bearings that Nortons used for a (short?) while apparently did have some sort of taper ground into the ends of them. Apparently Nortons soon switched to the FAGs - they were less expensive, and worked just as well. Fixed the Combat weak bearings saga right up.
But the myth of the barrel shaped rollers continued....

This was all covered in the Superblend bearing thread that went for 30+ ? pages not too long back.

How is an 'extra load roller bearing produced' ? The superblends fixed the bearing failure problem, is the material in the rollers and races better ? Or the finish of the internals ? Perhaps the claim that they fixed the problem is a myth ?

If you can't keep with others in the barnyard, maybe you should go to a lower class....

Obviously Nortons thought they had the main bearing failures solved.
If a roller bearing with say 9 rollers has say an extra half ton of load bearing capability than a 7 roller bearing,
then a heavy load environment is gunna need that extra capability.
If only Nortons had twigged to that before the Combat saga.

Go back and read the bearing thread for how many rollers various types of superblends actually have.
Folks showed plenty of pics of various types.
P.S. This has been known about, and published repeatedly over the past 40+ years,
its not exactly anything new.
Your 850 would have had the E bearing (extra)(heavy duty) from new on the assembly line.

Thanks for that. I've never had crank problems in Triumphs after we moveg to big journal shafts. We always treated the main bearings with suspicion, however the shorter stroke probably put less strain on the relationship. As far as my 850 goes, I simply accepted that the superblends were trouble free, and that's how they've been. No point in making a federal case out of something which is basically rubbish anyway.

comnoz said:

From the rough measurements I did on 750 crank some years ago they were approximately 25%-50%-25%. It is a tough thing to measure real accurately.
I have not tried to measure an 850 crank but I would bet it is similar.
Jim

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Getting the counterweights and flywheel just right to come out 25% 50% 25% would take some serious measuring and number punching. Anyone out there willing to scan a crank then solid model into a CAD program and calculate exactly what is needed? Seems like a huge project for someone other than me.

jseng1 said:

comnoz said:

From the rough measurements I did on 750 crank some years ago they were approximately 25%-50%-25%. It is a tough thing to measure real accurately.
I have not tried to measure an 850 crank but I would bet it is similar.
Jim

Click to expand...

Getting the counterweights and flywheel just right to come out 25% 50% 25% would take some serious measuring and number punching. Anyone out there willing to scan a crank then solid model into a CAD program and calculate exactly what is needed? Seems like a huge project for someone other than me.

Click to expand...

You could use water displacement to measure volume of crank material. Dip the crank end up to first counterweight. Mark waterline. Drop crank to cover first counterweight an mark waterline. Drop to next weight, mark line. Repeat for entire crank. Total weight of water shifted compared to total crank weight for accurate percentage and weight.

EUREKA Alan, but keep your suit on.

Sounds easy enough! ;-(

edgefinder said:

jseng1 said:

comnoz said:

From the rough measurements I did on 750 crank some years ago they were approximately 25%-50%-25%. It is a tough thing to measure real accurately.
I have not tried to measure an 850 crank but I would bet it is similar.
Jim

Click to expand...

Getting the counterweights and flywheel just right to come out 25% 50% 25% would take some serious measuring and number punching. Anyone out there willing to scan a crank then solid model into a CAD program and calculate exactly what is needed? Seems like a huge project for someone other than me.

Click to expand...

You could use water displacement to measure volume of crank material. Dip the crank end up to first counterweight. Mark waterline. Drop crank to cover first counterweight an mark waterline. Drop to next weight, mark line. Repeat for entire crank. Total weight of water shifted compared to total crank weight for accurate percentage and weight.

Click to expand...

That is a method I hadn't thought of. I will have to keep it in mind. Jim

Archimedes' principle indicates that the upward buoyant force that is exerted on a body immersed in a fluid, whether fully or partially submerged, is equal to the weight of the fluid that the body displaces. Archimedes' principle is a law of physics fundamental to fluid mechanics. Archimedes of Syracuse[1] formulated this principle, which bears his name.

The water displacement is measured for volume of the steel part then plug in the steel density then the shape for its moments of inertia. This is similar equations used in rocket science on orbiting objects around some common center of gravity, often for the sling shot effect to gain velocity.

Hobot says:

The water displacement is measured for volume of the steel part then plug in the steel density then the shape for its moments of inertia. This is similar equations used in rocket science on orbiting objects around some common center of gravity, often for the sling shot effect to gain velocity.

Hobot,
Your right, using liquid displacement to measure to CG of an irregular shape object is easier than using a lot of complicated measuring and formulas. But among other things it is also a good way to measure density.
i.e. You dunk two cylinder heads in a tank of liquid one at a time. They displace the same amount of fluid. You know the weight/volume number of the material. When you place them on a scale they have a different weights. Either the materials are different or one head has a bunch of voids. Probably not that important in the real world, but I find the theory interesting.

Ok after using Archimedes method to get the total mass of a part - in aviation they trace out the shape of the part then divide its area into two equal area parts and where they draw the dividing line is the center of air pressure or in our crank cheeks CoG of the part, more or less. Another way is cut out a similar shaped part in something easy then try to balance on a point, more or less - to find CoG of that shape part. Could give-pay an engineering student the task for a term paper with access to supercomputer program.

No need for supercomputer any more. My son uses a program called Matlab, operates on a run of the mill laptop. It can do anything from simple math to complicated integral equations. Myself, I have a phone that's smarter than me.

Ugh, I had to do the moments of inertia math by slide rule so good vision was vital as a whole grade point lost on each part per 1000 off, so even small calculators are super brains to me. My favorite was the circular slide rules that'd fit in shirt pocket with the pen and pencil pouch. .001" in these size slide rules was about equal to width of the lines, depending on the radius of the scale of course so a yard long slide would of been better for grades.

Same here, still have my first slide rule. Bought my first calculator in 1973. All it did was add, subtract, multiple, and divide. Cost $100.00.
But then there was Polish Notation (H.P.?) I think.

Hehe the world has left some our hard earned skills behind so may hang a slide rule on Peel for conversation piece labeled as engine computer. Meanwhile its basically trial and error that's refined Commando cranks not fancy calculations till after the fact.

It is not rocket science to recognise that an out of balance situation in the middle of a steel shaft will pull a bend into it if you spin it up. The trouble with the crank is the limitations the crankcases put on the size of the outer bob weights. A centre bearing would obviously help, however the oiling problems make that difficult, as in the Matchless twins. Sometimes we simply have to recognise the limitations of the design. My feeling is that a 750cc or 1000cc version of the Paton twin might be interesting. Or a 961 with a four valve cylinder head ?

Acotrel,

I was wondering if the is also a twisting component of the area between the connecting rods on the crank. As one piston is being forced down due to combustion the other piston is trying to draw a fresh charge of air/fuel into the cylinder causing a negative pressure.

Ugh = when Ms Peel stuck unloaded throttle event hit her second wind, apparently by fuel layer manifold puddle flash to full vaporization in hogged out over size HI Flow Combat head > with tach needle already on peg stop to rev'd up so much harsher it knocked my panic strenght re-grip of throttle so hard it threw my hand back so hard it made me stumble back again to make tach needle completely disappear bouncing off both side of the peg, she did not miss a firing beat so sounded life ripping fabric of space/time in closed tin shed, I wish I'd held WOT and only held kill button for 7 seconds to avoid the sucktion affect that I think actually bent Peels crank. It took about 3 second for tach needle to be seen as a blur, then 3 more to stop bouncing off peg back side then 3 more to slowling come down below red zone and stop. Next time out on Peel I'll have jank kill cord leash installed on me. Anyone pressing luck w/o also cryo tempering about everything is risking more than they have too. I do not think a cast iron flywheel would of taken this. Await report of anyone else's engine surviving well enough to keep riding 2000 miles up to 110 mph with huge winter screen on. Prior Peel would push it up to 125. No one here believes what speedo showed when naked and don't compute on the final gear ratio unless accounting for the sudden tire expansion that felt a bit like 5th gear over drive kicking in on pure toque power as rev's dropped to 6000 while speedo needle went too...

Peel crank had smaller lighter flywheel in case that's a factor to consider on next hi rpm crank design. Combat cases re-enforced, all stress risers welded and ground to radius then hammered work hardened in case that's what kept them re-useable as is.