timing gear

i just realized something... what prevents the timing set from getting out of line over time on a smallblock or any engine with that setup for cam operation? i was thinking, if one of the sprockets was just a little bit off, talking thousandths of a millimeter here, wouldn't that still be enough to throw it out of whack over a 10 year period? or do they just make them so exact that it doesn't matter...

Will it be off? Maybe. Will it still run good enough that you probably won't notice? Most likely. Timing chains are pretty reliable and if they are put on correctly from the factory, you may never need to worry about them. One gear is put on the crankshaft and usually is lined up by a key in the crank itself and will not move. Timing chains can stretch a little over time but I wouldn't worry. Timing belts on the other hand....