56 Water Pump pulley alignment

[Chuck B.]

I'm working on an engine that was put together a number of years ago, and if ever started was only run for a brief time. The water pump pulley is about 1/8" to far forward from the crankshaft pulley. I thought that possibly the engine builder had forgotten to put in the spacer behind the balancer, but when I pulled the balancer I found that the correct spacer is in place. The water pump is a 3704911 and I'm wondering if the pulley flange was not pressed on far enough to let the pulley line up with the crankshaft pulley. Does someone have the measurement of the distance from the cast iron housing to the back of the flange? I have another spacer that I could add to the one already there, but don't know if the balancer would press on far enough to be secure. There is no bolt in the crankshaft.Thanks for any help on this problem.Chuck Banks

[Joe L.]

Re: 56 Water Pump pulley alignment

I'm working on an engine that was put together a number of years ago, and if ever started was only run for a brief time. The water pump pulley is about 1/8" to far forward from the crankshaft pulley. I thought that possibly the engine builder had forgotten to put in the spacer behind the balancer, but when I pulled the balancer I found that the correct spacer is in place. The water pump is a 3704911 and I'm wondering if the pulley flange was not pressed on far enough to let the pulley line up with the crankshaft pulley. Does someone have the measurement of the distance from the cast iron housing to the back of the flange? I have another spacer that I could add to the one already there, but don't know if the balancer would press on far enough to be secure. There is no bolt in the crankshaft.Thanks for any help on this problem.Chuck Banks

Chuck------


Assuming that you are using the correct pulleys, I'd say your problem is exactly what you suspect-----the waterpump hub has not been pressed on far enough. In fact, just "eyeballing" the pump, that's exactly what it looks like to me.

I definitely would not recommend adding another crankshaft balancer spacer. What you need to do is to press the hub on the additional amount needed to align the pulleys. To do this right, you need to remove the pump from the engine. Then, remove the backing plate and support in an arbor or hydraulic press the rear of the pump shaft. Finally, press the hub on the additional amount needed.

[Chuck B.]

Re: 56 Water Pump pulley alignment

Joe,Thanks for the quick response. I'm probably better off to pull the pump to look inside anyway since I don't know the history of the rebuild. I would have thought rebuilders would have known the correct specifications for the location of the pulley hub.Chuck

[Joe L.]

Re: 56 Water Pump pulley alignment

Joe,Thanks for the quick response. I'm probably better off to pull the pump to look inside anyway since I don't know the history of the rebuild. I would have thought rebuilders would have known the correct specifications for the location of the pulley hub.Chuck

Chuck------



Yes, I would think so, too. The problem most likely occurred because of some confusion regarding hub positioning that does exist. There were actually 2 different hub spacing specs for 1955-70 Corvette small block waterpumps, each being different by 1/8". However, I believe all 1955 to at least 1963 pumps were the same spec. The "alternate spec" pump came into being sometime during the C2 period, about 1965 or 1966, I believe. But, this is all academic and your path is clear------you need the hub spacing it takes to align your pulleys. It's as simple as that.

[Chuck B.]

Re: 56 Water Pump pulley alignment

Joe, My water pump pulley is stamped 3788472 CG. This part appears to have been used on other SB Chevy engines. The correct number according to the AIM is 3704172 which was superseded by 3905995. My question is whether the pulley I have is the same dimensions as the 3704172. If anyone has either of the two correct pulleys, I'd appreciate it if they could compare their measurements to mine. Thanks, ChuckIMG_0402.JPGIMG_0407.JPG

[Joe L.]

Re: 56 Water Pump pulley alignment

Joe, My water pump pulley is stamped 3788472 CG. This part appears to have been used on other SB Chevy engines. The correct number according to the AIM is 3704172 which was superseded by 3905995. My question is whether the pulley I have is the same dimensions as the 3704172. If anyone has either of the two correct pulleys, I'd appreciate it if they could compare their measurements to mine. Thanks, Chuck[ATTACH=CONFIG]55116[/ATTACH][ATTACH=CONFIG]55117[/ATTACH]

Chuck-------



The GM #3788472 pulley was never specified for any Corvette application. It was passenger car only. However, there is a "connection" with the 3704172. It's like this:

The GM #3704172 was discontinued in April, 1973 and replaced by the GM #3905995. Both are 7-1/8" pulleys

The GM #3788472 was discontinued in April, 1967 and replaced by the GM #3905995 + GM #3720616 reinforcement. The GM #3720616 reinforcement is 1/8" thick. So, what this tells us is that the 3788472, by itself, will space 1/8" further out than the 3905995 (and, presumably, the 3704172 since the 3905995 is equivalent to the 3704172 without the spacer).

So, the above would explain your 1/8" discrepancy.

What to do? Well, I'd say either press the waterpump hub on the additional 1/8" as discussed earlier or replace the pulley with the correct pulley. You could also obtain a GM #3905995 and use as-is. It's discontinued but there are plenty around. What would I do? I'd replace the pulley with the correct3704172 pulley.

[Chuck B.]

Re: 56 Water Pump pulley alignment

Thanks Joe, I'll start looking for a 3704172 pulley. I'm happy to not have to pull the water pump to press the hub on another 1/8 ". Chuck