I've started this to keep some handle on Worty's problems, rather than it getting lost in the "What have you done" posts.
As I see it the choices are to swap the crank for a better one, or to fix the existing one. You could say the original crank is completely screwed and as such you can't make things any worse by trying a cheap fix.
If the bike ran smoothly, then the balance factor must be in the right ballpark, another thing to consider with a replacement crank. If it was always a bit of a bone shaker, a chance to make a change.
My first step would be to asses the wear on the journals. Badly scored or worn and no material left for a regrind, then it's goodbye to that one. It can be re-metalled, but here cost is the deciding factor.
So if it is worth proceeding, the problem is to make sure the oilpump worm runs true...looks like some material missing between threads and crank pinion... and secure and lock it to the crank. Hooligans way would be to tack weld the worm to the crank....if the crank's on its last legs anyway, this gives it a final fling.
The alternative would be to drill and tap the crank nose to take a left hand thread and locking bolt. Finding a tap and drilling accurately are the problems with this scheme. But an M8 left hand thread bolt is available from your purveyor of Cheap Chinese Mitre Saws. It holds the blade on. Looks like there is enough thread of sorts to locate the worm, Loctite alone is also worth a look if the existing threads will grip.
This can't be the first time this has happened, somewhere there is a specialised facility that could restore these threads...but of course the cost/benefit is the clincher to go this route.
Swarfy Cheapskate.
Additional. Wear limit on main and big end journals is stated at 2 Thou ovality. But if the crank will polish up OK, I would not hesitate to try a new set of shells on a crank with another thou or so of wear even if this meant a rough runner. Not ideal, but the difference between one that runs and one that doesn't. Timing bush wear is not a problem, grind to clean up the journal, custom bush made to fit.
Cylinder bore max oversize is plus 60 with common aftermarket pistons, reckon I have seen plus 80's somewhere. The existing bore needs to be checked, and if within wear limits, just given a light hone to break the glaze. Thick flange barrel casting is sought after, resleeve possible but not necessary at this stage.
