1987 Honda Civic timing belt

Generally some people will replace it according to the Honda spec book, but you need to consider the mileage of the vehicle and that it probably exceeds specs for maintenance intervals. Generally, 80 to 100K for miles is the right time to do the replacement. While in there, consider replacing the belt, the idler pulley, and the water pump.

Timing belt replacement will not have an affect on the smog testing capability or results. Timing itself might.