crankshaft radius

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How can it be that a crank that has been redone to have correct radius fillet be any more dangerous
than a crank that has been incorrectly ground to remove that fillet.

A few folks have broken cranks that have not been correctly (radius) done, but how many are still lurking out there with the same problem = no correct radius fillet.
Could be lurking in any Commando that you buy, and haven't inspected....

P.S. A lot of vintage and veteran machinery have had the cranks reworked to be useable, when you ask around and look.
A bit fragile back then, but modern methods can often reclaim them...
As long as they are steel, they can safely be welded. Although distortion is something to be countered against.
Cast iron is a different matter....
 
Risk assessment.

Bedford 1952, four wheels, desert terrain, max engine revs 2500 - 3000 say, multiple main bearing supports, may get away with fillet radius being welded to journals, worst scenario - bus breaks down, passengers disgruntled.

Norton Commando 1940s design pushed out to 1970s, two wheels, hilly terrain, max engine revs 7000, bolt together crank with known flex problem due to wide main bearing support, worst scenario - rider dead.

End.
 
So a crank is dangerous if its welded and the correct radius reinstated.
But plenty ? of cranks that have the radius removed aren't ??

We have recently seen here a whole slew of racing welded up and made up cranks shown.
7000+ rpms, routinely.
So why did no-one scream dangerous dangerous ?? !!

Welding steel cranks has been around for eons.
Heck, Kawa and Suzi cranks are welded in a variety of ways to strengthen them.
Some of the race car cranks have full circle crank cheeks added/welded to them.
Next you'll be telling us pistons can't be welded ?
Please, lets keep this discussion intelligent....
 
I just hope the original poster is provided with a replacement crank (comparable to the original) by the machine shop.
Welding fillet radii to Commando journals is substandard to the original even if it may suffice on old low-risk bus cranks or singles.
 
I worked at a place that regularly metal sprayed Diesel cranks. Had a service contract with Gardiner. The worn bits were always the journals.
Once reground the fillets were rolled.

One of the lads did his Alfasud crank, Took lots of time and care. Snapped like a carrot.
It is a very different thing building up a worn surface compared to working in a high stress concentration area like a fillet.

"I've cut it twice, and its still too short"
 
needing said:
even if it may suffice on old low-risk bus cranks or singles.
Click to expand...


Breaking crankpins is somewhat common on many varieties of older singles.
So any repairs have to be of a high standard.
We don't see any hysteria about this....

Bus cranks have to haul tons of passengers, plus the bus, so thats a fair old stress test....

Lot of articles out there about building up cranks to stroke them.
Not exactly trivial work.....
 
You seem to have invented a lot of broken bus cranks out of nowhere though ?

We are back to the ole factory machining errors inside the crank, are we.
Repent all ye Commando riders, and hope this doesn't happen to you.

Crank welding and regrinding is still a really common practice, despite all the hysteria.
Look at those beautiful radiiiiiiii...

crankshaft radius
 
Rohan said:
So a crank is dangerous if its welded and the correct radius reinstated.
But plenty ? of cranks that have the radius removed aren't ??

We have recently seen here a whole slew of racing welded up and made up cranks shown.
7000+ rpms, routinely.
So why did no-one scream dangerous dangerous ?? !!

Welding steel cranks has been around for eons.
Heck, Kawa and Suzi cranks are welded in a variety of ways to strengthen them.
Some of the race car cranks have full circle crank cheeks added/welded to them.
Next you'll be telling us pistons can't be welded ?
Please, lets keep this discussion intelligent....
Click to expand...

As soon as you weld it the fatigue limit drops to around 20% of what it was, and there is a huge chance of creating 'pre-existing' cracks
 
Rohan, your theories are wrong again but this particular theory has the potential to kill a person.
Buses, aircraft, jap cranks and other single journal throws between mains are not related to Norton Commando cranks with their bolt together, twin throw flexing cranks.
Even without finite element analysis data, the previous thread clearly shows cranks failing at journal fillet radius yet you insist that welding this region would not further significantly increase the risk of breaking. If you have practical and personal experience of welding this region and surviving I will stand correction.
 
needing said:
your theories are wrong again
Click to expand...

Which theories are "wrong again" ??

Commandos are hardly high performance exotica - although Norton cranks through the eons do have a bit of a history of breaking,
for various reasons.

Consult your local crank shop then, they will have considerable experience of welding and grinding performance cranks,
including strokers and big bores. See if they consider it do-able.
As said previously though, whether it will be cheaper than just finding another crank....

Just how many here get their cranks crack tested then, if this is such a "fatal flaw".
Have you dismantled and crack tested your crank ??

I am quite certain too that this would have been tried before today, possibly many times,
motorcyclists are just too parsimonious to fork out for a new crank every time one was needed in the past.
And someone would have tried it, just to see.....
 
Considering the number of stroked cranks there are around within racing where the crank pin is offset welded and the journal reground at a greater distance from the crank centre there are a lot of potential dead racers about going by Needing. As this method is even more reliant on the weld to be as strong as the original metal as welding back in radii then the lack of these dead racers means its a safe process. But then as I am another twit who bodged my ill fitting oil rings I could be wrong ;)
 
More history from beltdriveman 2005.
https://groups.yahoo.com/neo/groups/bsa ... ages/27908

Does moving the journal outward (re stroking the crank) reduce the stressor created by the drilling he mentions? I don't know except that the he states that the standard crank is inherently flawed.
I suppose the original poster has a standard crank but may now choose get it stroked if it corrects an inherent stressor at the fillet radius exacebated by its removal by the machine shop. Good luck.
 
Crank grinding specs from Norton published shop manual (no publication date):

650 & 750

crankshaft radius


500 Twins

crankshaft radius


Lightweight Twins

crankshaft radius


I agree w/ others who say plating WILL NOT provide stress relief radius. I am not an expert in welding technology, but if the crank were to be salvaged by welding, I would say it has to be done with aircraft welding technology (TIG) and then properly stressed relieved. Probably less expensive and less mental stress to buy another crank.

It may be possible to recover enough of the radius by grinding to the third level.... depends on how much the shop took off the first time.

Slick
 
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It is clear that plating does little or nothing for the strength of the crankshaft. We may only introduce the risk of hydrogen embrittlement.

I was wondering if laser welding could be an option here. Does any of you have experience with this process ?
 
If ya care to advance the data base of our mistreated Nortons at your expense I say have the crank cryo tempered then Nitrided then retouched to perfection. BUTT Realize THE ONLY way to ease everyone's mind on anything not perfect has long been settled by the few active Nortoneers online <<< *complete replacement* >>>, Period, End of Story, Throw int the Ole Towel and Go Home - so just filling in space and wasting everyone's entertainment time pointing out stuff other less inherit weak cranks get away with. Anything less than total replacement will be a a mark on your permanent reputation as reasonable owner mechanic so quite wasting forum time before tarting from $cratch on another crank.



On a side note, there are some new exotic coatings that essentially "glaze" the surface of steel, and force the molecules into a lower energy state than that which they'd prefer to be in. These "tortured" molecules (again, only at the surface... this coating is probably a few atoms thick) apply enormous force onto the part, essentially strengthening it by making it incredibly rigid. As an added benefit, the glazed coating is so hard and durable that it surpasses tungsten carbide and even some borazide ceramics in torture tests. Some really cool stuff on the horizon. This new process works on all ferrous metals, too.
Click to expand...
http://www.3si.org/forum/f42/re-nitridi ... nk-280627/
 
Welding would work. It's quite common practice to weld up journals to then re-grind when they have been previously ground down to the minimum.

It's also quite common to weld a journal so large it is then re-ground off centre, usually done to increase the stroke. Cranks done like this work fine, even in top end race bikes.

The real question, as Comnoz has already stated, is: is it financially viable when compared to simply getting another crank?

Why not get it welded and increased the stroke? Turn a disaster into an improvement??
 
Do people actually stroke Norton cranks by offset grinding? They would get a bit thin on one side of the journal, due to the sludge trap. Triumph/BSA triple cranks are welded up & offset ground on a regular basis, but these have solid journals.
 
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