1979 small block pulleys

[Kurt]

My corvette came with four pulleys unnattached to the engine. Two are crank, two are water pump pulleys. Many diagrams show three pulleys on the crank. Am I missing a pulley? It is an L-48 with A/C. Here are the numbers on the pulleys:
3991425BX, 330556AS (WATER PUMP), GM346290AB, 3956664CF (CRANK)

Thanks, Kurt

[Joe L.]

Re: 1979 small block pulleys

Kurt----

Well, you have some correct pullies and some incorrect pullies. First of all, there were NEVER 3 pullies on the crank nor were there 3 pullies on the water pump for ANY Corvette application. For 1979, there were 2 pullies on the water pump IF the car was also equipped with the air injection reactor system. If so, there was ONE single groove pulley and ONE two groove pulley "sandwiched" together. If you have an L-48 without air injection, then only the two groove pulley was used.

For the crankshaft, there were TWO pullies. The outer pulley was a ONE groove pulley and the inner pulley was a TWO groove pulley. The 2 pullies were "sandwiched" together.

Your GM #3991425 is the correct OUTER waterpump pulley. However, this pulley is used ONLY if the car is equipped with air injection. The inner pulley that you have, GM #330556, is NOT a Corvette pulley. It was originally used on some mid-70s passenger cars, Chevelles and Camaros. It is designed for use with a "long" waterpump. Originally, your 79 was equipped with inner waterpump pulley GM #346299. This is a 2 groove pulley. It is discontinued but it's replaced by GM #14023159 which is still available for a current GM list of $52.81.

Your outer 1 groove crankshaft pulley, GM #346290, is correct for your application. This pulley is 6-11/16" OD. The 2 groove inner crankshaft pulley, GM #3956664, that you have is incorrect. This is also a passenger car, Chevelle, and Camaro pulley used from 1969 onward. Your original inner crankshaft pulley was GM #469558 and was 7-3/4" OD. It's discontinued, but it's replaced by GM #14023151 which is still available for a current GM list price of $41.88.