Correct Water pump question
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Joined: May 2022
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From: Connecticut
Correct Water pump question
Looking for correct water pump for my 427 engine, did it come with long or short? Everything I see says I should be looking for short one? Is this correct? Mine had water pump on it but with the rebuild looking to put back all correct parts this is the last as it had everything except was using electric fuel pump but found correct 40659 pump now need water pump
Melting Slicks
Joined: Nov 2006
Posts: 3,380
Likes: 1,800
From: Apple Valley, MN
I found this on a old post by member Joe Lucia:
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.
From Bill Mock’s website, the big block water pump casting numbers are: 3856284, 3940960, 3992077 and 386100. I believe the 3856284 would be correct for your ‘68.
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.
From Bill Mock’s website, the big block water pump casting numbers are: 3856284, 3940960, 3992077 and 386100. I believe the 3856284 would be correct for your ‘68.
Last edited by 69L88; Aug 29, 2023 at 11:06 PM.
Thread Starter
Advanced
Joined: May 2022
Posts: 69
Likes: 14
From: Connecticut
I found this on a old post by member Joe Lucia:
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.
From Bill Mock’s website, the big block water pump casting numbers are: 3856284, 3940960, 3992077 and 386100. I believe the 3856284 would be correct for your ‘68.
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.
From Bill Mock’s website, the big block water pump casting numbers are: 3856284, 3940960, 3992077 and 386100. I believe the 3856284 would be correct for your ‘68.
Melting Slicks
Joined: Dec 2014
Posts: 2,771
Likes: 2,296
From: Central UT
https://www.ebay.com/itm/17525550215...Bk9SR8bkjPvIYg
https://www.ebay.com/itm/31473880887...Bk9SR8bkjPvIYg
Lots more to choose from. Best, Paul
https://www.ebay.com/itm/31473880887...Bk9SR8bkjPvIYg
Lots more to choose from. Best, Paul
