where do i find a pulley like this for my water pump on an 81. what is the difference between a corvette pulley and the other 350,s...... is it just the centre locating shaft size or are the 4 mounting holes in different positions?

 

Usually the difference is in the number of grooves, and the height of the pulley. Diameter plays a role, but that can be accommodated with different lengths of belt. Vettes have a short water pump, which might make the height of the pulley different than most other models.

http://www.zoops.com/product-listing.asp?ID=4

 

March can provide Corvette specific pulleys. Get the product id numbers off the March web site and order them from Summit

 

A "real" Corvette water pump uses a heavy duty 3/4" diameter shaft. A "standard" short Chevy water pump uses a 5/8" diameter shaft. March does not offer the 3/4" hole pulleys, so you have to have a machine shop open up the hole for you, and you have to make sure they do it concentric with the pulley OD. I've used several March components on Vettes, and I've always had to have the water pump pulley machined to fit. The 4-bolt pattern is the same and does not need to be changed.

 

thanks lars . is there any reason i cant get the correct size drill bit and whaammm drill that sucker as there is already a 5/8 centred hole there for me. !!! i thought someone out there would do one in this style especially for the corvettes.

 

The pulley uses the center hole for its concentricity alignment. In order to prevent a visual wobble of the pulley, concentricity between the center hole and the OD needs to be within .002". There is no way you're going to wack a 3/4" drill bit through a 5/8" hole and hold anything closer than .030" concentricity, which means your pulley will wobble like a drunken ***** if you don't do the work on a lathe.

I asked March about the 3/4" shaft issue. Their response was simply that there isn't enough demand for the 3/4" shaft pulleys to justify producing them. So you have to do the machine work yourself unless you want to swap out water pumps with the whimpy 5/8" shaft pump.

Here is a photo of a March system after machining the water pump pulley for the 3/4" shaft. The pulley was run in a 4-jaw chuck on a lathe, and the OD was dialed in to within .001" concentricity before the center hole was opened up to .751". This produced a perfect slip fit over the pump shaft, and the pulley runs perfectly smooth and in alignment:

Also keep in mind: The March accessory bracket systems are only designed to fit certain year heads with specific bolt patterns: If you use the brackets on other year Chevy heads, you have to re-machine the cylinder head accessory bracket mounting holes (heads shown here were re-machined to allow use of the March alternator bracket).