T&T: Hand turning an engine

[Bob]

In both manuals for Cat 3208 and Onan MDJF (15 KW) Gen Set, reference is made
to turning the engine over by hand, while checking or setting the valve
clearance for example... but it doesn't explain how to turn the engine by
hand.  I assume you will have to vent the cylinders somehow... maybe by
pulling out the injectors?  Or is there an easier way... then how do you turn
the crancshaft?

Would appreciate hearing about this from any members on the list who have done
this.

Thanks.