Originally Posted by
onehundred80
I agree my last statement is a bit erroneous, but torque is dependent on many variables and the same torque can apply different forces on the bearing, a lubricated thread will exert more pressure, a material with greater friction will exert less pressure and so on. So the correct material, formed to the correct profile and finish is required so that the specified torque gives the safe end load.
You need to remember that when you change the variables, you change the outcome. I was talking about different materials in like situations. If you really want to get crazy, you can say that using loctite on a bolt with a high enough RMS could be just hand tight. At the end of the day, this bolt needs to meet 4 conditions, it needs to be the right thread size and pitch, the correct length, be hollow for venting gearcase pressures and have a tensile strength high enough for the recommended 25nm torque plus 20%.
Originally Posted by
onehundred80
Tubes are notoriously weak when end loaded and crush relatively easily, a ball raceway that is buckled will not last too long. If you can break a bolt like this using a strap wrench I would suspect that the bolt is meant to fail before the end load was too great for the longevity of the bearing.
Actually, tubes are tremendously strong when end loaded and actually crush with much more effort than a similar square or other broken straight plane support. This is why we have round supports for bridges and the like. What I think you're trying to say is the tensile strength of a tube isn't as great as that of it's solid core variant. This would be correct. Just for argument sake though, if I had an M6 solid and an M12 hollow, the M12 would stretch less and fail with significantly greater force. That is unless it's walls were only as thick as tin foil.
Originally Posted by
onehundred80
The smaller bearing used on this pulley could possibly require less torque on an OEM bolt to prevent distortion than when used on the OEM bearing. It all depends on the new cross section and ball raceway depth.
This was already taken into account and is why the bearing spacer is made from aluminum and not stainless.