1974 Corvette. Unknown Engine year but appears to be the right period. It could be the original. Engine block was decked and numbers not restamped. The previous owner put the wrong pulley on the water pump, or possibly the Crank Pulley. It is a short water pump. The rear pulley grooves, which run the Alternator, line up correctly. The second groove, which will run the AC compressor, does not. The upper pulley 2nd groove is about 1/4 inch to far forward. If I measure the bottom pulley the width of the section with the two grooves is 1 1/4 inch. The top pulley measures 1 1/2 inch. The difference is the thickness of the ridge between the grooves. It is thicker on the top pulley and puts the groove to far forward.. The grooves themselves appear a little wider on the top pulley. I am trying to find the correct pulley for the water pump but none of the suppliers list those measurements. So, I do not know which pulley is correct. Do I change the top pulley or the bottom pulley. Also the top pulley measures 3 inches overall. Might be 3 1/16 inch. Also the Crank pulley has 3 grooves. The third, or front, groove runs the power steering. It also is a little out of alignment. It looks like it needs to come forward a bit. But I have not had any problems with it. I am installing the vintage air sure fit replacement AC system and need the pulleys to align correctly. Any ideas on which pulley to change? And how do I order the right one if they do not list those dimensions?

 

Do you have the correct water pump?

 

It does appear to be the correct water pump. I realize I should wait until I have the Vintage Air AC kit and install the Compressor to see which pulley I will line up with.

 

That is a good plan!

 

I have the compressor installed and it lines up just fine with the water pump pulley. I don't think it needs to line up with the crank pulley too. I will run the compressor off the water pump pulley only unless there is some reason it has to run off the crank pulley as well. Seems like it should be fine

 

Don't like the sound of that. You will put too much stress on the W.P. bearing. The A/C has to be run off of the "power pulley" which is the crank. Not off of an accessory pulley.

 

I did some checking and you are correct. Probably not a good Idea. I also looked a little closer and used a straight edge to check the alignment of the pulleys. The water pump pulley is a full 1/4 inch to far forward of the AC compressor. The compressor lines up much closer to the crank pulley. I will have to find the correct water pump pulley. Considering how far away the compressor is from the water pump it would probably be ok but the 2nd position V groove is to far forward of the 2nd position Crank pulley. I will have to replace the water pump pulley. Now to find one

 

Try to find a stock, direct fit unit. I tried numerous chrome / polished / billet pulleys to no avail. Either the wrong diameter, the wrong pilot hole, the wrong bolt pattern spacing or the wrong spacing from the W.P. hub. I gave up and still have the stock unit.

Correct unit:
Maybe Corvette Central, Keen or Zip Corvettes? IDK, but double check on the pilot hole & shaft, they changed.

 

I am at a loss here. I find several for sale but none with dimensions and can't seem to get an answer from the sellers on ebay. I've called a few Vette parts dealers and still can't get an answer. It looks like the original part number is 3991424 for a small block Corvette 1974 with short water pump but no one can give me the dimensions so I can be sure it will work on my Corvette. It needs to be 3 or 3 1/16 inches deep and the width of the 2 grooves is 1 3/16 inch. That's what the width of my Crankshaft V grooves is. It had the wrong after market chrome Water Pump pulley on it when I bought the car. I ordered a new pulley from Corvette Central and it was wrong but it worked for the alternator so I used it anyway because I did not have air. Now I have the AC installed and need the right Pulley. Very frustrated at this point. Does anyone know how I can get the dimensions of Water Pump Pulley part number 3991424. I don't want to just start ordering pulleys and hope I get the right one.