crank arm coming loose

left crank arm has recently started coming loose, have took them off and put back on a few times. they are suginos 75 square tapers, using campag iso centaur bb (old style version). i dont wanna have to tighten too much cos thinking the taper might deform and bottom out. but if that happens then thinking i could use a jis equivalent width to remedy...? thinking also to put some sort of shim between the crank and bb axle that would provide more contact/tighter fit?

Sounds like crank arm is fucked and will only get worse every time it wriggles loose.

thanks for your input, but am looking for a fix not an inevitable scenario if i do squat

If you can bottom out the crank on the bb i.e., the bolt flange touching the end of the bb axle, then the crank is irretrievably fucked anyway. AFAIK the shim you suggest doesn't exist. My research suggests that fears of deforming the crank taper by over-tightening are unfounded, so just put the merest suggestion of grease on the bb tapers and tighten it hard. I wouldn't use an extension bar, but plenty of oomph on a standard Allen key should do it. If you're really concerned ask your LBS to use their torque wrench on it.

EDIT: This assumes that the tapers are in reasonable shape. If you've been riding the bike with the cranks loose, then they may well be deformed already and need binning. Pictures would help.

its fucked, not fixable

@pifko is right

Don't listen to the internet-mechanics: use Sugru to shim it.

A shim does exist. We call it a beer can. It would need to be cut accurately to fit all four sides of the spindle end, forming a nice neat bodge.

The obvious solution is to laser spot weld the crank arm to the BB spindle.

Thanks for all input, has anyone ever crashed and died from crank arm coming off?

thanks for your input, but am looking for a fix not an inevitable scenario if i do squat

https://www.dolan-bikes.com/sugino-cycle-components/sugino-track-cranks/sugino-sg75-crank.html

HTH

Actually - https://www.ribblecycles.co.uk/sram-omnium-chainset-inc-gxp-cups/
or
https://www.dolan-bikes.com/sugino-dd75-chainset.html

HTH

Took it off too swap with my ominiums, and there is plenty of taper inside, so aint bottomed out, probably wasn't torqued enough. Just needed a gym membership.

If it came loose while you were riding it, it's fucked.

The fact that it keeps coming loose is a clue.

By all means use the correct torque now, in the vain hope that this will miraculously fix the problem.

But it won't.

And "no", you can't shim it. Especially with aluminium (aka beer can).