I have a 71 big block car with a build date of April 29 and i am a bit confused about which water casting number is correct for that car. the serial number is 115834. I have a copy of the ncrs technical information manual but either i am not reading it right or it is confusing. thanks in advance. Sheldon
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Re: 71 Big Block Water Pump?
Sheldon-----
Your car was originally fitted with a GM CASTING #3992077 waterpump. Virtually no doubt about that, at all.In Appreciation of John Hinckley -
Re: 71 Big Block Water Pump?
Joe's dead right about that. I went through that when I pulled the water pump off a '77 454 in my '70 LS-5. The odd thing about the removed pump was that it is a 1971 big block pump. I still have it and was okay when it was removed. The NCRS manual didn't reference the pump for the 1970 454 Corvette but through several board members and two pump rebuilders I have a correct rebuilt pump for the '70 454 engine I bought to replace that '77 454 engine.
ScottComment
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Re: 71 Big Block Water Pump?
You have to watch the water pump shaft sizes on hose years. We sold a 1974 454 water pump for a 1970 454 C-3. The shaft size was smaller and it broke the shaft and threw the fan into the hood. The manufacture (wont mention names) would not stand behind it as my counterman thought he said "74, 454 vet" and in fact he said "he said 70, 454 vet". Any way it cost us money. DaleComment
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Re: 71 Big Block Water Pump?
Thanks for the info. Do the water pumps have a date code cast in them?Comment
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Re: 71 Big Block Water Pump?
Sheldon:
Yes. My '71 454 'vette is vin #15065, build date April 20, casting # is as Joes states. Casting date is A 27 71Comment
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Re: 71 Big Block Water Pump?
Dale-----
Yes, the big block waterpumps did change from 1970 to 1971 in more ways than just the casting. Small blocks did, too, but small blocks changed a lot more than big blocks. Here's the deal for big blocks:
There were 4 different castings used for big blocks in Corvettes over the 1965-74 period. These are GM #3856284 (1965-E1969), 3940960 (L1969-1970), 3992077 (1971-72), and 386100 (73-74). ALL of these castings are functionally interchangeable, all use a "jumbo" sized bearing, and all use a 3/4" shaft.
However, the 1965-70 pumps use a 5/8" pilot on the shaft and a waterpump hub with a 3" bolt circle (or, a dual pattern bolt circle). The 71-74 pumps use a 3/4" pilot and a 3-1/4" bolt circle hub (or, a dual bolt pattern hub).
ALL of the above are "short leg" style waterpumps. NO 55-91 Corvette, big block or small block, EVER USED A LONG LEG WATERPUMP. NONE. EVER. PERIOD. The short leg waterpumps were also used on ALL Chevrolet V-8 engines, big block and small block, from 1955 to 1968. After 1968, all Chevrolet V-8s, big block and small block, changed to the long-leg style waterpumps EXCEPT Corvette and some MD/HD trucks. So, the GM #3856284 casting was used for ALL big blocks during the 65-68 period. The other castings were used only for Corvette and MD/HD truck applications.
Beginning in 1971, Corvette small blocks and big blocks used the 3/4" pilot as did MD/HD trucks. ALL others continued to use the 5/8" pilot, even though ALL small blocks changed to a 3/4" shaft size in 1971 (big blocks were always 3/4" shaft size).
Now, the foregoing is all background and here's where things get "tricky": a 1971-74 Corvette big block waterpump configuration cannot be used on a 1965-70 Corvette, assuming that the 65-70 has all of its original fan drive and pulley system. The 3/4" pilot will not fit the waterpump pullies and it will not fit into the fan clutch pilot hole. Also, if the waterpump hub is single pattern, as many 71-74 pumps were/are, the pulley/fan clutch bolt holes will not align. So, installation is "impossible" (not for "bubba, of course, who will "ream out" and "re-drill" the pulley and fan clutch holes).
However, a 1965-70 big block waterpump CAN be installed on a 1971-74 Corvette. The 5/8" pilot shaft of the 65-70 pump will fit, "sloppily", the 3/4" hole in the 71-74 pullies and the 3/4" pilot hole in the 71-74 fan clutch. Since many 65-70 big block waterpumps were fitted with dual pattern hubs or are fitted by rebuilders with dual pattern hubs, the pulley bolt holes will align.
Now, the REAL tricky part which everyone that does this misses, is that while a 1965-70 waterpump can be installed sucessfully on a 1971-74 Corvette, a PRECISION BUSHING TO INCREASE THE EFFECTIVE SIZE OF THE PILOT SHAFT FROM 5/8"' TO 3/4" MUST ALSO BE USED. Without this bushing, the pullies and fan clutch will NOT be perfectly aligned, significant imbalance will result 99% of the time, and RAPID AND CATASTROPHIC FAILURE of the waterpump and/or fan clutch is practically ASSURED.In Appreciation of John HinckleyComment
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Re: 71 Big Block Water Pump?
As usual Joe is on the money. I can not say that I have ever used an early pump and later fan, I have experienced the catastrophic failure of using an early fan (yep, we drilled it} on a later pump. Summer 1981, my buddy's '73 big block. We were both 19 and knew it all, we had an earlier fan clutch off my '69 z/28, and we proceeded to make things happen. Ten minutes later when we hit 5 grand the clutch snapped off and the fan went straight through the radiator. We were supposed to be headed to the beach that night to chase women, instead we spent the weekend chasing a radiator.Comment
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Dating
All BB pump housings were dated. For SB pumps, the dating process depended upon the specific casting number and source of the casting (Saginaw vs. Tonawanda). Saginaw didn't begin putting cast dates on SB water pump housings until roughly the 1964-65 time frame. Tonawanda dated their 'equivalent' water pump housings as far back as 1960 (maybe even earlier)....Comment
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Re: 71 Big Block Water Pump?
John-----
Yes, attempts to modify the early style fan and fan clutch to work with a later style waterpump and pulley system will result in the exact same conditions that are caused by using the early waterpump on the later applications without the bushing I mentioned. What results is an imbalanced assembly that will "self-destruct" VERY rapidly, often taking other components with it. Hoods, radiators, fan shrouds, radiator hoses, alternators, inner fender wells, etc., are frequent "victims".In Appreciation of John HinckleyComment
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Re: Dating
Jack,
FWIW -- my 1967 Chevelle 327 has an undated 608 water pump. I am 99+% sure it is original to the engine. Good news is NCRS won't be judging it, and I doubt the Chevelle guys will get that chance either.TerryComment
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That's good news, Terry...
because the JG books for mid-year Corvettes do not bar judges from attempting to read/verify water pump cast numbers/cast dates as the 'enlightened' policy of the early Shark cars. So, it's a judge's choice issue on whether or not you should attempt to read/verify casting numbers in the mid-year era and the various JG books define when date coding began on various Saginaw/Flint housing castings with the '608 version of the pump said to have been dated starting in mid-64 while the '326 pump is identified to have begun dating in late '65.
An NCRS 'purist' going from the book would conclude your Chevelle's pump must be a service replacement because it's past the 0-6 month general guideline AND it's undated....Comment
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Re: That's good news, Terry...
"An NCRS 'purist' going from the book would conclude your Chevelle's pump must be a service replacement because it's past the 0-6 month general guideline AND it's undated.... "
Yep, I'm aware of all that Jack, and it is the reason I posted what would otherwise be off topic information here. Saddly I have not owned the car its entire life, so I can't be 100% sure of its heratige.TerryComment
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