Picked up a 312 crank cheap with this repair ...keyway piece welded back in place, timing gear slides on without the woodruff key in place, seems to go on too easily. Question is, would you trust this repair or is this a scrap crank?

I would trust that repair on a mostly stock street engine.  I would be more concerned about the loose fitting gear.  How loose is it?  Is the damper also loose?  Someone may have taken a light cut on the snout and made the components too loo

John - "The Hoosier Hurricane"

The timing gear slides on easily and without the woodruff key, it also will spin easily. With the TRW gear there is less play as it has only one keyway slot. The multi-keyway gear is noticeably looser with less "meat" touching the crank. The damper slides on with little effort as well. With the damper key installed the damper takes little effort to seat and can be pulled back off by hand. The crank gear with a key installed can still be wiggled back and forth ever so slightly. The crank snout measures 1.249 at the front and decreases to 1.2483 as best I can measure. I think the damper would be OK, but the gear wouldn't be good.. I'll take it to a shop and see if there is some repair that is affordable  and will give the proper fit.

the crank is cast iron,welding cast iron is very trickey,it can work on cylender heads if heated to near melt and re machined, but on crankshafts,especialy that aria that is weak to start with. my opinion is take it to the scrap and save your self alot of trouble down the road.It looks like the damage was from a timing gear failure. the key way will neve last.with the damper loose that makes the the crank worth its weight as good cast at the junkyard.

It probably isn't worth the cost, but the snout can be chrome plated and reground to size.  There are also places that can metal spray a shaft to repair a worn or undersize condition.  Does not create the heat that welding does.  Electric motor repair shops use these two methods to save the rotors in large motors.

John - "The Hoosier Hurricane"

I like John's thoughts.  Plating the snout and then finishing it to size sounds like a reasonable approach with no heat involved.  The flame spraying technique is interesting, too.  We had a Eutectic torch unit for metal spraying at work.  Heat was involved to accomplish bonding, but it was not a fusion weld to the base metal piece.  We used the technique for building up shafts while they were spun on a lathe.  The surface was turned down afterwards to the appropriate diameter.
Another out-of-the-box idea that crosses my mind is knurling the undersize surface on a lathe and then turning the surface to the correct diameter.  I'd use a diamond pattern knurling tool rather than a straight knurl.  -The idea is the same as what was once common practice on piston skirts.  SLIGHTLY increase the diameter for refitting purposes.  While the diamond knurling tool would be used, the impression in the crank snout surface would only look like an 'X', not the pointy gripping surface we see on tools like some ratchets or drive punches.  The material next to the 'X' impression is displaced, i.e., pushed out to increase the diameter slightly.As was suggested, I suspect someone took a light finish type cut to clean-up the surface perhaps related to the welding of the damaged keyway.  On a metal lathe, IF the tailstock is not properly aligned with the headstock, the turned surface of a shaft will have a slight taper, i.e. one end will measure different than the other.  Another possibility might be that the end of the crank positioned in the chuck was not accurately centered.

NoShortcuts
a.k.a. Charlie Brown
near Syracuse, New York

Would it be possible to turn the damaged snout down undersized an put a sleeve into it? Pete

industrial chrome could work if not for the key situation,but to chrome you need to true up the crank grind it afew thou then chrome then grind again. when i worked we had bucket pins and shafts when gears when pressed on. the proses was not sucsesfull on cranks,most broke,tho that was diesel engines.i would think very pricey endever. 

Back-in-the-day, late '60s... early '70s before they closed, Crankshaft Company in CA used to offer hard chroming of crankshafts...Gosh.  That was a while ago!   

NoShortcuts
a.k.a. Charlie Brown
near Syracuse, New York

Per John Mummert's web site @ http://www.ford-y-block.com/crankshaftid.htm, the crank snout is supposed to be 1.250!  You're not 'off ' very much even if your mic calibration isn't spot on.
I'd pursue the notion of knurling the slightly undersize surface.  Pushing a minimal 'X' pattern into the surface will grow the diameter AMAZINGLY well!  With so little to be 'added' to the diameter, final fitting of the timing gear and damper may best be accomplished using just a long angle lathe file to smooth the knurled surface slightly afterwards and make the necessary 'fit' adjustment.    Let us know how you make out...


NoShortcuts
a.k.a. Charlie Brown
near Syracuse, New York