Nissan Repair: timing, incomplete combustion, engine knock

Question
what really happens when you advance and retaed the timing on a pathfinder, 1990, 4wd

Answer
Advancing the timing will cause the spark to fire early, before TDC, so when the piston is on the up stroke, it fires, and slams the piston against the walls of the cylinder. This is what causes engine knock.

Retarding will do the opposite, firing the plug too late, you get incomplete combustion and loss of power.

aloha
calvin