1971 Water pump casting number, confusion w/ the judging manual

[Billy S.]

Hello,

First things first; I love the new manual, thanks to all who put it together!

Now onto my question -- I am reading about water pumps it says (PG 152):

"For 1970 350s, the casting number is 3782608; 1971 and early 1972 style is 3991399..."

I have a car built mid December of 1970 (clearly its a 71 model). Which water pump should I have? Technically my motor was built in 1970, but are the years referring to calendar years or model years in the judging manual?

Thanks!

[Patrick H.]

Re: 1971 Water pump casting number, confusion w/ the judging manual

Model years, always, unless otherwise indicated.

3991399 is correct for your car.

[Terry M.]

Re: 1971 Water pump casting number, confusion w/ the judging manual

Hello,

First things first; I love the new manual, thanks to all who put it together!

Now onto my question -- I am reading about water pumps it says (PG 152):

"For 1970 350s, the casting number is 3782608; 1971 and early 1972 style is 3991399..."

I have a car built mid December of 1970 (clearly its a 71 model). Which water pump should I have? Technically my motor was built in 1970, but are the years referring to calendar years or model years in the judging manual?

Thanks!

The reference is to Model Years (MY). However there is always a chance of hold-over, but December is way far into 1971 model year for this feature.

One of the differences between the 3782608 and the 3991399 is the diameter of the pump shaft (the 399 is larger diameter) and this dictates a larger bolt hole circle for the fan clutch and pulley. Unfortunately I can't recall the numbers of the shaft or the bolt hole circle, but maybe someone who is not yet traveling to the National Convention will post those numbers. That might lead you to a clue as to the original water pump if the fan clutch and/or pulley on your car are original.

[Billy S.]

Re: 1971 Water pump casting number, confusion w/ the judging manual

Thank you Patrick & Terry.

My feeling is that I should have the standard 1971 water pump 3991399. The fan & fan clutch appear to me to be original and when I compare them to other 1971 cars they are the same.

Billy

[Joe L.]

Re: 1971 Water pump casting number, confusion w/ the judging manual

The reference is to Model Years (MY). However there is always a chance of hold-over, but December is way far into 1971 model year for this feature.

One of the differences between the 3782608 and the 3991399 is the diameter of the pump shaft (the 399 is larger diameter) and this dictates a larger bolt hole circle for the fan clutch and pulley. Unfortunately I can't recall the numbers of the shaft or the bolt hole circle, but maybe someone who is not yet traveling to the National Convention will post those numbers. That might lead you to a clue as to the original water pump if the fan clutch and/or pulley on your car are original.

Terry------


1970 waterpumps have a 5/8" shaft; 1971+ pumps have a 3/4" shaft. The pulleys used with the 2 waterpumps are different and non-interchangeable.

[Rick N.]

Re: 1971 Water pump casting number, confusion w/ the judging manual

Not only are the shaft sizes different, but so is the 4 bolt, bolt circles.

[Joe L.]

Re: 1971 Water pump casting number, confusion w/ the judging manual

[QUOTE=Rick Newman (63908);834361]Not only are the shaft sizes different, but so is the 4 bolt, bolt circles.[/QUOTE


Rick-----


Yes, that's one of the reasons the 1970 and earlier pulleys are not interchangeable with the 1971 and later. The other reasons are the pilot hole size and the fact that the hub spacing on the 1970 and earlier applications is slightly different than the hub spacing on the 1971+.

[Rick N.]

Re: 1971 Water pump casting number, confusion w/ the judging manual

[QUOTE=Joe Lucia (12484);834392]

Not only are the shaft sizes different, but so is the 4 bolt, bolt circles.[/QUOTE


Rick-----


Yes, that's one of the reasons the 1970 and earlier pulleys are not interchangeable with the 1971 and later. The other reasons are the pilot hole size and the fact that the hub spacing on the 1970 and earlier applications is slightly different than the hub spacing on the 1971+.

Why would the flange spacing be different? The crank pulleys are the same.

[Joe L.]

Re: 1971 Water pump casting number, confusion w/ the judging manual

[QUOTE=Rick Newman (63908);834411]

Why would the flange spacing be different? The crank pulleys are the same.

Rick------

I can assure you the water pump hub spacing was different for 1970 and earlier versus 1971 and later. My recollection is that the 1971 and later had the hub spaced out ABOUT 1/4" compared to previous. The configuration of the water pump pulleys "compensated" for this and allowed the pulley grooves to match up to the crank pulley which was, indeed, the same one used for some earlier applications.

The above only applies to small blocks. While the pulleys also changed for big blocks for 1971 due to the 3/4" pilot and consequent larger bolt circle mounting pattern, the hub spacing for all 1965-74 big block water pump hubs was the same.

[Rick N.]

[Rick N.]

Re: 1971 Water pump casting number, confusion w/ the judging manual

I just did a comparison. Looks like the two pulleys are spaced differntly. The later waterpump would have to have the flange further out from the pump. Good call Joe !!!