We are having a problem with the pinion key routinely falling out during use. We had it cable tied which helped for a while but it recently fell out again and chipped the pinion near the notch (see photos). Does anyone have any suggestions on why this is happening and what to do to prevent & repair? One thought is that this is really a fly-wheel key and not a pinion key. Also, the crank shaft has a little play (if I pull on the flywheel it slides about 3/4?”), is that normal? Thanks for your help!
FYI: This C&P Old Style 8x12 is at the Atlanta Printmakers Studio and gets a fair amount of use (generally 3 days a week) from a variety of printers.

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You might try bending the key a little so it arches up out of the slot, pressing harder against the inside of the pinion gear. But be sure you have the right size (width and thickness) key, too — if it’s too small it will let the pinion gear rotate slightly on the shaft, wearing the shaft and the slot.

A square key isn’t right for that. You need a “gib head key” which is slightly tapered and has a right angle at the outer end. It wedges into place and doesn’t slip out. (Square keys are used when there is a set-screw to hold it in place.)
MSC sells them, and you can purchase online once you set up an account.

Thanks for the help! I found the gib head key at McMaster-Carr and just need to figure out what size to order.

I was looking for a key for a 10x15 new style and was told that, for the 10x15, the key might be 3/8 in square, with taper and maybe 3 inches long. Not sure what the differences are between the 8x12 and the 10x15 but thought this might help you get an idea of sizing. Probably smaller than this for the 8x12?


it looks in the pic that some damage has already been done. i would stop using the press until the proper key is in place. (gib head) measure the width of the groove in an undamaged section of the crank. any play here allows for more damage to be done. as for your crank moving in and out, look for one of the frame bearings to be possibly pushed out of the frame. there should be no side/side play in the crank. maybe the bearing on the op side has a lock collar? set screw?