Originally Posted by
DannoXYZ
That's kinda overtightening it at 40-lbs. But you're more likely to cause damage by under-tightening them.
No, by tightening them that much he's more likely to damage them to overtightening. Which he is doing by an extreme margin, already. 35Nm for square taper cranks with 8mm hex bolts is generally enough. And that is quite tight already
All it takes is for them to come loose just once and you've buggered the square-taper hole and it'll never, ever fit right again.
And all it takes is for one slide too far on the spindle if you overtighten.
I've found it's a lot more secure to replace the flat washer with a star-lockwasher if you're going to be removing the cranks a lot. Reduces the chance that a well-used bolt with worn threads may come loose. Usually a good practice to use new bolts every 10th time you've re-installed the cranks.
Bolts come loose because of inadequate torque. If you're really that worried about it coming loose treat the threads with loctite. Which really ins't necessary. Using a star washer only serves to damage the crank.
The better solution for the OP is to stick a cartridge bb and forget about having to regularly overhauling the bb and it's subsequent problems. Time to get with the 21st century.