Sorry, Min. Somewhere in a text book, but I have been too busy to research it. There are 2 basic formulae, one for a pin fitted in the con-rod and rotating at the piston bearings (diagram 4. SIMPLE BEAM- UNIFORM LOAD PARTIALLY DISTRIBUTED ) , one for the pin fitted in the piston and rotating at the con-rod small-end bearing (diagram16. BEAM FIXED AT BOTH ENDS- CONCENTRATED LOAD AT CENTER).
For Fatigue I would use max calculated stress must be below 0.1% of the proof stress for the pin material.
Of course the bearing loads are relatively easy to calculate.