Rebuilding Twin Crank Via Welding/Spraying?

[peterg123]

It's very hard to find cranks not ground to 60 and I have even seen 80 on the centre bearing. Is there any way Gleeson submerged arc weld rebuilding or Metal Spray techniques can be used to build up a twin crank and then grind back to STD, as can be done on the steel cranks of other makes?

Sadly someone stole 4 AMC cranks, 2 of them Noddies, off me a while back and 3 were decent, otherwise I would not be asking!

[Groily]

Might be worth having a gander at what Ernie Merryweather said years ago on going to 80 under (along with other useful observations). 'Not probably very desirable' on balance, although it had seemingly been done OK.
One of the areas of sensitivity is the closeness of the oil drillings to the big-ends to the surface of the journals where the drilling comes across from the centre main - there's not a whole lot there . . .
So, if we assume it's not a great plan to keep on grinding away . . .

T&L Engineering, much recommended on here, told me some time ago that 'Yes', they could bring worn cranks back up to standard dimensions, and had successfully done so. Last resort, obviously, but 'do-able'.
IIRC, they said it was important for structural integrity that the original radii had not been lost - because adding a few tens of thous max on top would not transform a sow's ear into a silk purse. That sounds logical, but not being a metallurgist . . . and not being au fait with the way molecules go round corners to maintain a fluid 'grain' in the various different materials one can use . . . daren't say more.

At the time, the shortage of good cranks was for 650s more than for the others, so the conversation was 650-centric, but I came away believing it could be done without undue risk, for a 'normal-use' engine anyway. The subject under review was a Meehanite one, at that (which fortunately in the end came out good within the 'normal' range, so we didn't go the 'build-me-up-buttercup' route).

The 650 problem became moot for many of us when the Club invested in the new 650 cranks, on which the current view seems to be 'unbreakable'. One hopes, I have a couple of them! But if a metal-spray or similar option was considered a not-too-high-risk route on a 650, it's probably a fairly safe bet on the 500/600s. Certainly worth chatting to Barry at T&L I would have thought, to get his latest take on this.

That's the optimistic bit, supported by reasonably contemporary conversations . . . .
Less happily, in about 1980 I had a 500 crank built-up, but the result wasn't good. It broke in short order, because either the radii under the build-up were poor to start with - it was at 80 under, BMC Mini-shells fitted, or the firm that did the work took 'em off in the process. We shall never know - but there are probably still shards of metal deeply-embedded in the tarmac of the A1 near Hatfield in England which bear witness to the failure.