I am making a bracket for the idler pulley on my zetec and I am making a sleeve for the 18mm hole in the pulley. The question is what size bolt is strong enough to take the forces from the pulley?

Not sure how to calculate it other than if it looks right. M6 looks too small but M8 looks ok. M8 works better for me than M10 as I am also buillding a screw thread belt tensioner into my bracket and the smaller the better from a fit point of view

Most adjustable tensioner pulleys on factory engines are mounted with an M8 bolt.

Depends on how its done but m8 is fine on mine, plenty of clamping force between the bearing carrier and bracket.




[Edited on 15/6/13 by big_wasa]

use a high tensile bolt of grade 10.9 or 12.9

clamp force will be as follows for M8x1.25:-

10.9 - 15 KN - Tightening Max 31 Nm
12.9 - 17 KN - Tightening Max 33 Nm