Reground Cranks

[adamand]

On a recent VMCC run (Humber Bridge) riding at around 40 mph I heard a distant rumble from the engine, to cut a long story short, I got the bike engine stripped and was amazed to find the crank had sheared in half. Never known this to happen on a large journal BSA crank. Anyway further investigation showed that on a previous regind some dipstick had taken out the radii. So my point guys is if your having a crank reground then make sure they do not take out the radius, otherwise you too could have a crank like mine.  Ed

[muskrat]

Sound advise Ed. the LJ's are more robust but not indestructible. I've had a few SJ's go, and at 100mph they take everything else with it 
Cheers

[MG]

Yep, the influence of sharp notches and diameter deviation on the fatigue behaviour of dynamically loaded parts.
There've been literally thousands of scientific works published on that.

Each engine reconditioner worth his money should know that the radii are essential.

It might not really be much comfort to you, but be glad it didn't throw a rod and damaged the crankcases or cause even worse damage to bike and health.

[adamand]

Muskrat ,MG.   Thanks for your comments and yes I was very lucky that the crank was the only damage, interestingly whilst waiting for the recovery vehicle, I kicked her off and she started (didnt at that time know the crank was gone) soon switched off though. Alls well that ends well, replacement hens teeth crank located, sludge trap cleared (solid) reground and she's nearly rebuilt. 

[Mark Parker]

I noticed in Roland Pikes writings they cured the S/J crank breakage by rolling the radius, it compresses the metal deeply and makes it much more difficult for it to open up into a crack and then break, from memory, I think it took their machine 5-10 min to break a good std crank and they left the rolled radius crank on it for an hour or so with no problem. They recommended it to the factory but the LJ cranks were already on the way, it would be a good way to do the radiuss, some diesel cranks are done that way, and some crank grinding people probably have the facility to do it.

[BSA_54A10]

And you are all waiting for me to say this so i won't dissapoint you.

While it is out, off to the heat treaters & get it nitrogen toughened should cost around £ 20.00 could save your life, real cheap isurance.