Tool to radius PTO shaft

jseng1 said:

Here's a photo of what I think is a Ron Wood race crank with the radius PTO shaft and heavy metal in the cheeks to redistribute weight closer to the outside to reduce flex. This was back in the days when one piece cranks were hard to come by. It solved crank breakage but then the cases started cracking.

My race cranks stayed together when I radiused the PTO stub (after checking with magnaflux). I checked my 850 race cases and found 7 cracks. So I reinforced the cases by welding a plate around the drive side output.

Then I had Wiseco make my first lightweight pistons (around 1987) and all my breakage problems went away.

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That's one of my early 750 race bike cranks,, Jim. It was modified by machinist Will Fitzenheimer back in 1978. It has the same mods that he made for Ron Wood back when Ron was still using stock cranks (Ron later went to one piece cranks made by Moldex). Will machined a new steel flywheel(using a copy of the factory drawing, that he had talked Norton into providing!!!), radiused the mainshaft jjoint into the cheek, inserted heavy metal slugs in the cheeks, shot peened the whole thing, and fitted it together with AN studs and nuts. It worked great for many years, and I still have it stored in a box on the shelf. It also had thin plates welded to the flywheel side of the cheeks, to get even more balance weight out closer to the main bearings. I've attached a couple of other pictures showing the details. Fun stuff from my early racing days. Hard to believe that was 47 years ago.

For anyone interested, he cut the radius with a ground tool in the lathe, pretty much the same way Jim described above, but he did the final smoothing with a shaped wood stick and grinding paste, followed by shot peening.







Ken

A lot of nice work but it just makes me think of the need for a one piece crank. Goodness sakes, even Enfield had one. Yes, I know that Norton didn't have the dosh to upgrade even the machine tools but how much difference would it have been in the big picture? Less parts, less assembly time, fewer broken cranks...

Onder said:

A lot of nice work but it just makes me think of the need for a one piece crank. Goodness sakes, even Enfield had one. Yes, I know that Norton didn't have the dosh to upgrade even the machine tools but how much difference would it have been in the big picture? Less parts, less assembly time, fewer broken cranks...

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They didn’t even need to do that if you think about it.

These guys modified the stock cranks… it would have been very easy, and low cost, for Norton to add things like the undercut radius machining to their machining processes and make the cranks better from the get go.

No doubt a good one piece forging is better from a design perspective. But the ‘bolt up’ aspect is not the weakness. Even Maney and Molnar cranks are bolted up. They do not fail at the studs.

Technical paper on fillet rolling of crankshafts:

But what is the advantage of bolting up? Ill ignore the mistake of mass in the middle for now.

Onder said:

But what is the advantage of bolting up? Ill ignore the mistake of mass in the middle for now.

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Cheaper / easier to manufacture.

acadian said:

Technical paper on fillet rolling of crankshafts:

https://www.shotpeener.com/library/pdf/1970002.pdf

View attachment 119558

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No question that putting in a rolled radius would be best, but finding someone to do it to a Commando crankshaft was difficult/impossible back then, and maybe still now. Cutting a recessed radius fillet and getting the crank shot peened was easily accomplished back then, at least here in SoCal. If I ever do another crankshaft like that, I'll see how available the service is. But I might not ever do another one. The one piece cranks available now look pretty good.

Ken

Rolled radius seems to be something done for general automotive work now. Makes sense if you have someone tooled up to do it.

lcrken said:

No question that putting in a rolled radius would be best, but finding someone to do it to a Commando crankshaft was difficult/impossible back then, and maybe still now. Cutting a recessed radius fillet and getting the crank shot peened was easily accomplished back then, at least here in SoCal. If I ever do another crankshaft like that, I'll see how available the service is. But I might not ever do another one. The one piece cranks available now look pretty good.

Ken

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The paper is old but what's apparent is that this is a factory only procedure, there's a pic of the unit itself