drive side crank
 

Thanks in advance for any advice. I have recently rebuilt an ~84 Bianchi (Japanese) and replaced the bottom bracket with a square tapered cartridge. My issue is the driver side has come loose a couple of times with minimal mileage (around 10). The socket has no visible deformity but I don't have a tool to measure or Mic the inside. The cranks are the original Sugino and I am wondering if they need to be torqued to a minimum ftlb or if I need to replace the cranks.

Most square taper are 40ft/lbs for the torque spec. And yeah, torquing to the correct spec is highly adviseable, or they come loose and egg the holes in the cranks. Sugino should have torque specs somewhere on the web I'm sure. I'd find what they call for rather than blindly following the 40lb, although that should be close.

40 Nm or 40 lb/ft? I really don't know but 40 lb/ft seems pretty damn tight (40Nm is 29.5 lb/ft).

Square taper cranks generally take 35ft/lb+

You don't need to guess. If the cranks come loose after apply appropriate tightening torque they're hosed. You have nothing to lose, really by trying.

How do you determine that it's loose? This is not a trick question. Does it wobble? Or are you testing the tightness of the bolt?

you did use the correct taper cartridge BB yes? JIS I think right gentlemen? if you used a Campi or some other Italian designed to fit pre 95ish Campi cranks the different taper may be adding to your woes

25 to 32 ft pounds of torque. http://www.parktool.com/repair/readhowto.asp?id=88
Do not retorque. The arms will try to move away from the bolts and the torque will go down slightly. http://www.sheldonbrown.com/brandt/i...ng-cranks.html

To follow on to this, if you have a mis-match, then the crank might go on too far, so that the BB is flush with the crank opening. Thus the bolt cannot press the crank tighter, because the bolt is now pressing against the BB and crank at the same time. You could remove the bolt and verify that the bb axle is still recessed, not flush with the crank.

A very noticeable wobble.
I think so, I am using an English threaded Shimano BB that I was recommended by my LBS.

40 Nm or 30 ft-lb. (ft-lb = Nm * 0.75).

Sugino probably uses a JIS taper (vice ISO). But taper isn't necessarily a problem - both use the same taper angle. The issue is more a matter of where the crank sits on the taper.

What did you do to correct the wobble? Retighten the bolt? If so you're probably hosed as riding a loose (wobbly) crank arm distorts the hole and ruins the arm. Replace the arm and this time tighten the bolt correctly.