How do you change the belt from the engine to the transmission on an older (1995?) john deere 170 lawn tractor? A diagram would be most helpful.

Hi,
I do not know of a set of directions. You must take the idler loose at the engine. There is a crossbrace across the middle of the frame that must be taken loose at both ends and rotated out of the way to get it above. Idlers have to be loosened and the brake engaged.
Understand that the idler near the engine must be in the middle of the "J" slot when tightened or it will not disengage properly.
Peace,
Clarke