It connects the crankshaft and the camshaft so the valves open and close at the proper time. Isuzu recommends changing the belt every 60,000 miles. If the belt breaks, the valves stop moving but the pistons don't. The pistons hit the valves, bending them and sometimes breaking the piston. Since major engine damage can result if the timing belt breaks it should be changed soon.
Preventive maintenance is worth the money.
I have a cartridge type grease gun. Dear Toby, Grease can easily be applied with a cartridge grease gun. Pump grease into the fitting until you see grease begin to work its way out of the greased joint or coupling. The appearance of grease coming out indicates that the new grease is pushing the old grease out through the joint. It is like the car can't decide where to idle.