Did your stock Commando crank blow at 8,000 RPM?

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we know that TC ran over 120 WOT 150 8000+ rpm shift points
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everything that I have read says that the Hogslayer had only two speeds and they were controlled by a true
"slipper" clutch and shifting mechanism, being the first motorcycle dragster of that design, and it is pointed out that this is what allowed the gearbox to take the loads
 
Call TC -as apparently did not always automatically shift on time or prior when TC worked shifter. I'm not brave as TC with cast iron but he got away with it in a lot of short brusts, but could we now with more decades of time and vibes working lurking. The highest intentionally rev'd Peel with spiffed up crank was 7600-ish>88-ish in 2nd a few times because the pull kept increasing. Cast iron is said to respond to cryo tempering but don't know if that'd heal a prexisting fault line.
 
acotrel said:
I believe a standard commando crank would cop 8000 RPM, but not for long . I think (know) that if the crank has the standard balance factor it would destroy the cases with the offloading at high revs. When even a rebalanced crank is running at high revs it probably has a bow in it at revs other than for which it has been rebalanced. The fatigue aspect of the bolts which hold it together then becomes important if the crank is regularly subjected to high revs. The other thing is the fatigue effect on the aluminium rods when the inertia of the pistons causes stretch at high revs - the loads are higher at high revs. My approach is to use the revs for which the bottom end has been designed, and direct all engine mods at increasing torque, rather than top end horsepower. In any bike the gearbox is extremely important. If the torque output is increased, gearing for it can become a problem when first gear in a close ratio box becomes much higher as the overall gearing is increased to use the extra mid-range urge productively.
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Can we point out again again again that crank balance factors don't ever prefectly balance the crank - they only make it comfortable for the rider.
You seem to sprout words that suggest you think that crank balance is some magic number that makes everything behave as in some perfect world....

AND, even if the crank was perfectly balanced, that still wouldn't stop it bowing if it wasn't rigid enough to keep itself perfectly straight and true at high rpms.

Lecture No 1 in engineering 101 is that a fly landing on a massive bridge will cause it to bend, slightly.
Now, calculate how much it will bend.
Then, if 100 heavily laden lorries are crossing it, calculate how much it will bend.
You start to get the picture...
 
Rohan said:
Would all those who have seen 8000 rpm on the tacho, and 2 seconds later your crank disintegrated, please respond here.

Might be a mighty short response list here too ??

Guess its all in how the question is framed, isn't it....
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Bring it round , and we'll see . :P :lol:
 
BSA did research I posted in the crank porn thread the found least all around stress on the crank was gotten in the low 50%, just like Norton issued, though of course I forget if they referenced that as dry or wet. Found the cases we've seen here and my own witness cases - thank goodness the pistons resist jerk down makes the flywheel aim at the ground...

I saw a friend's car after a flywheel exploded and there is no way of adequately describing the damage without seeing it first hand. My friend's car had massive damage afterwords and it was equipped with a Lakewood scatter shield and a block plate. Even with those two items the engine blew up, pulled all the bolts through the cast iron they were connected too, cut the input shaft off of the transmission, tore the shifter in half, tore up the drive shaft, and sawed the right header in half. Only God and Lakewood saved his feet. Put a piece into the hood also which tore up the distributor cap on the way by. Nothing in a car's drivetrain can do as much damage as an exploding "CAST IRON" flywheel. It ruined everything from the radiator to the rear end. On the plus side he has never run another one to this day. The cause is "continued heating and cooling cycles from using slicks that cause cracks in the cast iron. Eventually those cracks cause catastrophic failure of the iron flywheel. Steel doesn't do this and can be brought back to as new by resurfacing the face of the flywheel. P.S... I've also seen a Ford nodular iron wheel flywheel do the same thing, it didn't tear up as much but it did "mushroom" the Lakewood and ruined it too.
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More of this in this forum bantering to reflect on while whizzing that ole Norton's heart out.
http://www.chevelles.com/forums/showthread.php?t=237136
 
I still have a video clip of Martin Brundles Peugeot engined car on the F1 starting grid, where the lights go green and the clutch can be seen departing his car and hitting the wall, with flash of flames and sparks. And the commentary saying "thats the 2nd time in a row that has happened.".

Don't what this has to do with flywheels, but it seemed relevant - he didn't even get 2 seconds of motion out of it... !!
 
hobot said:
BSA did research I posted in the crank porn thread the found least all around stress on the crank was gotten in the low 50%, just like Norton issued,
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Did they define how they measured stress levels in "the crank" ???

And if the crank will hold together no matter what, what about the poor old rider. ??
Its no good if he and the bike gets shaken to bits, to lessen the stress levels on the crank. !
 
I did not study the BSA study just took in its BF implications, you'll have to scroll the crank porn thread or search it up and see the graph and values and tell us how they did it. Obvious higher BF takes more counter weight which means more sling force for f/w to resist, even if feels smoother to the bike and pilot - till it bails out. This is a stilly thread in a couple of ways, one, very few risk even redline let alone 8000 and those that did and cracked up likely won't admit it here or are even lurking on this forum. Also likely those that did and cracked up in distance past and survived - extended that dare devil habit on other cycles they didn't survive so we would never know. On the other hand plenty of other things can let go and take out cases but crank survives fine.

F/w exploding is an ancient favorite gearhead subject with the often repeated show stopper story of horizontal experimental energy storing test that let go with a fella standing in line that got cleaved down his center.
 
I would agree - we'd imagine that few folks nowadays are going to subject their bikes to big handfuls of revs, in road use anyway.

But enough folks have already replied here with stories of revvy bikes that we can be fairly confident that cranks aren't going to explode within 2 seconds of doing a little over redline. If your cam and valve springs are even man enough to get there, rpm wise !
 
...and yet none of this discussion (apart from, apparently, TC & SOME racer's <not firsthand> efforts) touch on anything beyond an occasional "peek" at 8,000 RPM; NOT nearly representative of the statement that (paraphrasing) "new Commandos were often run over 8,000 with no rod failures", to which I originally replied that it wouldn't be the rods that went first.

I'm still NOT AT ALL convinced a STOCK Commando crank with stock pistons and rods can out-live any regular running over 8,000 RPM.
 
Smith tachs in good condition register accurately well past 8000 rpm, but they do have a bit of delay to register the rise above 8000 rpm so have to hold it .5 sec to get correct reading.
 
rohan,rider comfort is a consequence of rebalancing a crank to suit high revs, it is not the primary reason for doing it in a racing motor. the main reason is to avoid the big bang when the bearings and cases self destruct.
 
acotrel said:
rohan,rider comfort is a consequence of rebalancing a crank to suit high revs, it is not the primary reason for doing it in a racing motor. the main reason is to avoid the big bang when the bearings and cases self destruct.
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Not in any of the engines I've had to do with, folks I have spoken too, or engineering books on the subject.

Balancing a heavy spinning disk with heavy reciprocating rods and pistons is never going to be perfectly balanced.
You can balance it at 0%, 100%, or somewhere in between.
And, over the years, all these factors have been successfully used somewhere.

Back in the 1920s, about 50% was commonly used.
But then engine revs rose, and they found that anything creeping towards 80% or more could happily be used.
This is only a matter of a few extra, more or less, ounces...

But depends almost entirely on the particular frame its being used in.
These days, computer assisted vibration analysis takes a lot of the guesswork out of it.
One of the guys I worked with at some point had done a lot of research into this (the computer side of things).
Bridges and crankshafts are not that distantly related = strange stuff. !!
 
grandpaul said:
...and yet none of this discussion (apart from, apparently, TC & SOME racer's <not firsthand> efforts) touch on anything beyond an occasional "peek" at 8,000 RPM; NOT nearly representative of the statement that (paraphrasing) "new Commandos were often run over 8,000 with no rod failures", to which I originally replied that it wouldn't be the rods that went first.

I'm still NOT AT ALL convinced a STOCK Commando crank with stock pistons and rods can out-live any regular running over 8,000 RPM.
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Why don't you accurately quote what I said.
Not paraphrase it to something it wasn't.
 
I'm still NOT AT ALL convinced a STOCK Commando crank with stock pistons and rods can out-live any regular running over 8,000 RPM.
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of course you are not convinced

the Norton factory agrees with you, they who built it put a redline limit on it

what exactly would be the point of revving a stock Commando motor in excess of the factory redline anyway?

ok I can see being an occasional hooligan taking it to 7000, but why go farther when one just shifts into second or third or fourth at 7000rpm?

why risk your motor for the dubious thrill of a couple hundred more rpm?
 
As I said/meant originally, when these were new the guys doing the roadtesting commented that it was possible to rev them past 7000 in the lower gears.
And the only 750 I've ever ridden would do this, on just a quick squirt around the block.
And it didn't have a redline on the tacho. (what year does that make it ?).

The early old all iron iron dommies were recorded as roadtested with more than 6500 rpm in the lower gears, when this was more than 'redline'. ?
Not that they had a tacho, so these numbers were calculated.
And they just gave it a handful until it stopped acelerating, so they changed into a higher gear - noting the speed on the speedo they did so.
 
Rohan said:
As I (typed) originally... "Road test reports of Commandos when they were new frequently refer to the fact they will willingly rev to 8000 rpm (plus !), a fact which was said to contribute significantly to short main bearing life."
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Sure doesn't read the same as your statement above, that you "meant" to say...

(oops, you were only off by 1,000 RPM)
 
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