BB68Vett

What is the difference and what does it refer to? Does my '68 427/390 have a long or short water pump. Thanks for any replies.

Tahos

1968 and older BB and SB had shorter W/P than 1969 and later W/P.That is
for all but Vettes.I believe ALL BB vettes have the shorter pump.

LAvetteman

Never seen a long one on a big block

rrent

I've got the long pump set up on my '67 elCamino. I bought parts for a '72 Chevelle. This will never work on a Vette - just not enough room for the power steering pump and who knows what else would hit what else.

If you are looking at a pump on a motor the long will have an inch maybe a little more between the pump back and timing chain cover - the short maybe 1/2" or less.

Joe Lucia

"BB68Vett"-------

ALL Corvettes with big block engines use the "short" water pump. This includes ALL 1965-74 models.

For other Chevrolet passenger car models with big blocks, ALL 1965-68 use the "short" water pump. All 1969-75 use the "long" leg water pump.

Also, the functional difference between the "short" and "long" leg water pumps is the distance from the block mounting surface to the face of the fan/pulley mounting flange. The "long" pumps have a greater distance between the two and, in appearance, the "legs" (which are the two portions of the casting the ends of which mount on the block) are longer than on the "short" style pumps.


[Modified by Joe Lucia, 11:15 AM 9/1/2001]

BSeery

To add even more confusion, there is one more type of chevrolet water pump out there. The Corvette pump.

The water pump on the C3's is different than the normal short or long water pump. It has a 3/4 inch shaft instead of the smaller, normal shaft.

If you are buying a pump, make sure it says "Corvette" in the listing, if not, it's not the right pump.

rrent

BSeery - I am a firm beleive in the theory: there can never really be to much confusion. :D

Does the larger shaft water pump include both big and small block pumps?

Joe Lucia

BSeery------


The "Corvette short" water pump which you refer to applies only to small blocks and not big blocks. ALL 65-74 Corvette big blocks use the same, BASIC water pump casting (although 4 different castings were used). All 65-70 big blocks use a bearing/shaft assembly witha 3/4" diameter shaft, but a PILOT (the end of the shaft which centers the pullies and fan clutch) turned down to 5/8". 1971-74 big blocks use a full 3/4" pilot.

For Corvette small blocks, ALL 55-70 Corvettes use a "short" water pump with a 5/8" shaft. This same style water pump was also used on all 55-68 small blocks used in all other Chevrolet passenger cars with small blocks. In 1969, most Chevrolet small blocks and big blocks, EXCEPT CORVETTE, went to the "long" water pump which still used a 5/8" shaft.

In 1971, virtually ALL of the small block water pumps changed. All, EXCEPT CORVETTE, continued to be "long leg" style but with 3/4" shaft and 5/8" pilot. Corvette continued to use a "short leg" water pump, but it was a DIFFERENT short leg water pump than used for 55-70 Corvettes. This water pump, often referred to as the "Corvette short" water pump, was set up to accomodate the large bearing and shaft assembly which used a 3/4" shaft. For 71-82 Corvette pumps, the shaft PILOT was the full 3/4". The full 3/4" pilot small block water pumps are unique to Corvettes and some medium/heavy duty trucks which also used the "Corvette short" water pump. I might also add that 71-74 Corvette big blocks ALSO used the 3/4" pilot shaft and they were the only big block water pumps which did so.

Due to its design, the "Corvette short" water pump has a slightly greater block mounting surface-to-face of hub flange dimension. Combined with the fact that the 71+ pump has the full 3/4" pilot, it is applicable to only 71+ model Corvettes (and the trucks mentioned). The "Corvette short" water pump is NOT applicable to 55-70 Corvettes unless the entire pulley system, fan clutch and fan are changed to the 71+ configuration.

I might also add here, for clarification, by water pump SHAFT diameter, I am talking about the portion of the shaft that goes THROUGH THE BEARING. All Corvette water pumps use a 5/8" impeller shaft end. For 65-70 small block Corvettes, this means that the shaft is 5/8" all the way from end-to-end. For 71+ Corvette small blocks, the impeller end of the shaft is turned down to 5/8".

There were several GM castings used for the 55-70 Corvette and 55-68 ALL small block "short" water pumps. However, for the 71-82 "Corvette short" water pump, there were only 2 castings ever used. 1971-early 1972 used GM #3991399. Later 1972 to 1982 used GM #330813. These are the only 2 castings which GM EVER used for the "Corvette short" water pump. The 3991399 has no drilled and tapped boss on the top for external bypass. The 330813 does have a large upper boss and 3/4" NPT fitting for external bypass. The external bypass provision was plugged with a square head pipe plug for all 72-82 Corvette applications. The fact that this boss and tapping was added to the pump was only for the truck applications that also used it.


[Modified by Joe Lucia, 12:50 PM 9/1/2001]

BB68Vett

Wow! I certainly did get an education. Thanks for the reply. Talk about information overload. I'm just glad I have a big block, this makes my water pump selection much easier. Now...what is the right mounting set up? Bolts or some bolts and studs. I will start a new thread on that one though, probably in the Factory Correct Resto forum.

LemansBlue68

...I always thought pumps was pumps.

Bubba


(Thanks Joe, Now you've got me going out to my garage to see if the outfit that rebuilt my pump used the right shaft.)

BSeery

As I said, make sure it says "Corvette" in the parts listing for the pump that you want for your year.