1970 L46 water pump & pulley?

**Joe L.** · March 22, 2013, 08:25 PM

Re: 1970 L46 water pump & pulley?

Originally posted by Mike Furline (53259)

I need an education on a water pump and pulley.

I have a 1970 L46 (350/350HP), with Power Steering, no A/C, no A.I.R.. The "installed" water pump has been rebuilt twice in the last 30 miles or so, and the pump shaft is loose again. As RPM increases above 3000rpm you can see the fan assembly/water pump pulley start to wobble.
Not sure if it's the rebuilders fault, the pump is past the point of a decent rebuild, or the pulley/fan/clutch assembly is out of round/balance and wiping out the water pump bearing.

So I'm starting from scratch and ordered a water pump from Bill Mock (NCRS #93). He informed me that 1969 & 70 Corvette water pumps have an eight hole flange. (My current installed water pump has four.) Any particular reason for the eight holes?

Started searching for a two groove pulley (P/N 3890419) which most descriptions list as a 66, 67, 68 327 water pump pulley. I then called Paragon and Corvette World to ask a few questions, neither of their catalogues list a pulley for a 70 350/350. Neither could answer why they don't carry a pulley or what it should be. They both are going to get back to me when they find an answer.

So, what pulley do I need? Should the pulley have eight holes to match the water pump flange? Should the fan have eight holes to match up?

Any ideas on best way to check my fan for balance, alignment, etc.?

TIA,
Mike

Mike-----

The waterpump pulley you require was originally GM #3848904. This is a deep groove, 2 groove pulley. It has a 5/8" center pilot hole and FOUR pulley mounting holes on a 1-3/4" bolt circle. It was discontinued in September, 1972 and replaced by GM #3995641. The latter is still available from GM for about 90 bucks, GM list.

Some original 1969-70 waterpumps did have an 8 hole flange. This is a dual pattern flange used for applications using either the 1-3/4" bolt circle or the 2-1/8" bolt circle. ALL 1955-70 Corvette small blocks use the 1-3/4" bolt circle. Some 1969-70 waterpumps originally used a 4 hole flange. My original-owner 1969 was one that did. It does not matter which you have. No one will know the difference once the pulley is installed on the pump. In general, PRODUCTION waterpumps had 4 hole flanges whereas SERVICE waterpumps had 8 hole flanges but exceptions exist both ways.

As far as your rapid-failing waterpumps go, it is highly unlikely that the waterpump casting is at fault. Usually, the only thing that causes a casting to "die" is corrosion damage (but many do suffer from significant internal corrosion damage). What causes waterpumps to fail in short order is excessive runout on the flange. I believe this is why GM OVERHAUL manuals after 1970 no longer included procedures for waterpump rebuilding and GM discontinued most internal SERVICE parts for waterpumps. After about that time, GM considered waterpumps to be SERVICED as a complete assembly only. It is possible to field SERVICE a waterpump but one has to be sure that excessive flange runout is not created during the assembly. It's often difficult to do this, especially with a used flange.

Corvette fans have a 4 hole flange. All 63-70 fans use a 3" bolt circle.

**Terry M.** · March 22, 2013, 11:03 PM

Re: 1970 L46 water pump & pulley?

My 1970 (small block engine assembled 0114) has the 8-hole flange on the water pump that has never been off the engine. You will find many people who will tell you the 8-hole is a service replacement and ALL factory installed Corvette water pumps are 4-hole. Do not believe them. On the other hand I can not tell you that any particular stretch came with 8 holes, but Bill Moch pas probably seen more water pumps than all of us put together. Just remember what Joe said -- once you get it together the only one who will know is you.

**David L.** · March 23, 2013, 12:09 PM

Re: 1970 L46 water pump & pulley?

I have always assumed that SB Chevrolet water pumps with the 8 threaded hole hubs were either service replacements or rebuilt but today I have a different opinion.

I just did a little research on the hub with my vintage Chev. parts catalogs (Gr. 1.062) and parts history catalogs.

GM # 3836771 was replaced with GM # 3852830 in Oct. 1964 which was then replaced with GM # 3941054 in April 1970 which was then removed from service in Dec. 1971.

Here are my conclusions (or maybe assumptions):

3836771 - 4 threaded holes, 1 3/4" BC, 1955-1964 models
3852830 - 4 threaded holes, 1 3/4" BC, 1965-1968 models plus 1969-1970 Corvettes
3941054 - 8 threaded holes, 1 3/4" & 2 1/8" BC, 1967-1968 Z28, 1971+ Corvette, 1969+ other Chev. models

I do not believe that the 4-hole hub w/2 1/8" BC was ever serviced.

It seems very logical that the 1969-1970 Corvettes could have factory installed 8-hole W/pump hubs since both 1 3/4" and 2 1/8" BC hubs were used on 1969 and 1970 Chevrolet models, particularly for those engines made in Flint.

I wonder if the water pumps made in Tonowanda with the "T" casting during the 1969 and 1970 model years also used the 8-hole hub or did they just use the 4-hole 2 1/8" BC hubs. I have two "3927170" water pumps dated "A 27 70" and "A 13 70" with the "T" casting that have the 4-hole 2 1/8" hub. These water pumps are for my 1970 Camaro SS350 (orig. Tonowanda eng.).

Dave

**Joe L.** · March 23, 2013, 12:52 PM

Re: 1970 L46 water pump & pulley?

Originally posted by David Liukkonen (3775)

I have always assumed that SB Chevrolet water pumps with the 8 threaded hole hubs were either service replacements or rebuilt but today I have a different opinion.

I just did a little research on the hub with my vintage Chev. parts catalogs (Gr. 1.062) and parts history catalogs.

GM # 3836771 was replaced with GM # 3852830 in Oct. 1964 which was then replaced with GM # 3941054 in April 1970 which was then removed from service in Dec. 1971.

Here are my conclusions (or maybe assumptions):

3836771 - 4 threaded holes, 1 3/4" BC, 1955-1964 models
3852830 - 4 threaded holes, 1 3/4" BC, 1965-1968 models plus 1969-1970 Corvettes
3941054 - 8 threaded holes, 1 3/4" & 2 1/8" BC, 1967-1968 Z28, 1971+ Corvette, 1969+ other Chev. models

I do not believe that the 4-hole hub w/2 1/8" BC was ever serviced.

It seems very logical that the 1969-1970 Corvettes could have factory installed 8-hole W/pump hubs since both 1 3/4" and 2 1/8" BC hubs were used on 1969 and 1970 Chevrolet models, particularly for those engines made in Flint.

I wonder if the water pumps made in Tonowanda with the "T" casting during the 1969 and 1970 model years also used the 8-hole hub or did they just use the 4-hole 2 1/8" BC hubs. I have two "3927170" water pumps dated "A 27 70" and "A 13 70" with the "T" casting that have the 4-hole 2 1/8" hub. These water pumps are for my 1970 Camaro SS350 (orig. Tonowanda eng.).

Dave

Dave-----

The 3941054 hub could not have been used for 1971 and later Corvettes. The 3941054 is designed for use with a 5/8" waterpump shaft. All 1971 and later Corvettes used a waterpump shaft of 3/4" OD (except the impeller end which was always 5/8").

For 1969-70, the only vehicles that used the "short leg" waterpump without external bypass (i.e. 3782608 casting) were Corvettes. So, while all of these only required the 1-3/4" bolt circle hub, GM may have decided that they would use the same 8 hole hub for both PRODUCTION and SERVICE waterpumps (the SERVICE pumps manufactured during this period were applicable all the way back to 1955 although few would have required the larger bolt circle). They did not do it exclusively, though, since my original 1969 pump was a "4 holer". Most, if not all, SERVICE waterpumps for small blocks were manufactured at Flint.

The 4 hole 2-1/8" bolt circle hub for 5/8" shafts and the 2-1/8" bolt circle hub for 3/4" shafts were never available in SERVICE. There was no need for former because there was no 2-1/8", 5/8" shaft applications prior to 1969. From 1969 on the 3941054 would SERVICE all applications. As far 3/4" shaft hubs, there were never any applications that used the 1-3/4" bolt circle, so a dual pattern hub was not necessary. Plus, after 1970 GM stopped specifying overhaul procedures for waterpumps and rapidly phased out most waterpump internal parts. So, as far as SERVICE was concerned, the 4 hole 2-1/8" hubs were either not necessary (because an 8 hole dual pattern was available) or because the SERVICE requirement "died before they were born" (i.e 2-1/8", 3/4" shaft)

**Mike E.** · March 23, 2013, 01:35 PM

Re: 1970 L46 water pump & pulley?

70 #6243, unmolested and recently purchased from the original owner, has 608 wp dated A10 0 has 8-hole hub. And you CAN see that with pulleys, etc. installed.

**Jim T.** · March 23, 2013, 02:48 PM

Re: 1970 L46 water pump & pulley?

Original owner and still own my 1970 Corvette 350/300. Original water pump on my 1970 built in July 1970 (still have it) has more than the four holes on the flange. Only four holes in the original pulleys.

Replaced the 1970's original water pump that was leaking through the weep hole with a new TRW water pump in late 80's. Did not last, did some high rpms one day and the front bearing failed on the water pump. Was given a new TRW replacement and it failed quickly on a road trip leaking. Bought a rebuilt from auto parts store, it failed on the way home from the trip out of state in 1988. Bought another rebuilt unit that is still in use since 1988.

**Terry M.** · March 23, 2013, 10:37 PM

Re: 1970 L46 water pump & pulley?

Originally posted by Mike Ernst (211)

70 #6243, unmolested and recently purchased from the original owner, has 608 wp dated A10 0 has 8-hole hub. And you CAN see that with pulleys, etc. installed.

I guess that is another reason to come visit you again -- besides my buying lunch. You can school me on how to see the water pump hub with the car assembled. Oh, and then there are windshield wipers also. The excuses are mounting and Spring is here. LMK

**Joe L.** · March 23, 2013, 11:39 PM

Re: 1970 L46 water pump & pulley?

Originally posted by Jim Trekell (22375)

Original owner and still own my 1970 Corvette 350/300. Original water pump on my 1970 built in July 1970 (still have it) has more than the four holes on the flange. Only four holes in the original pulleys.

Replaced the 1970's original water pump that was leaking through the weep hole with a new TRW water pump in late 80's. Did not last, did some high rpms one day and the front bearing failed on the water pump. Was given a new TRW replacement and it failed quickly on a road trip leaking. Bought a rebuilt from auto parts store, it failed on the way home from the trip out of state in 1988. Bought another rebuilt unit that is still in use since 1988.

Jim-----

The most likely problem with the failed pumps was excessive runout on the hub OR a badly balanced fan/fan clutch assembly. Either of these faults will cause a waterpump to fail in short order. This is especially true for all 1955-70 Corvette small blocks which use a 5/8" shaft waterpump.

**Mike E.** · March 24, 2013, 09:41 AM

Re: 1970 L46 water pump & pulley?

Can't see all 8, but with a mirror can see a quadrant, and there is more than one and less than three in that quadrant. I used my math skills to do the extrapolation. It's obvious that I took a college math class already in high school, isn't it??

I need to get those wipers ready, and give you a call, Terry. Been trying to bring the 72 LS5 back to life first.

**Terry M.** · March 24, 2013, 10:50 AM

Re: 1970 L46 water pump & pulley?

I can tell by your questions the 1972 has occupied your time since my last visit. The weather will only get better the longer it takes for you to return your attention to the 1970. Those wipers have waited 43 years for me. They can wait a little longer.

**William M.** · November 15, 2013, 10:19 PM

Re: 1970 L46 water pump & pulley?

Sirs:MVC-001S.JPG MVC-004S.JPG
I just purchased a quantity of 3782608 water pumps that came on Corvette engines that were puchased by an automotive company that used the Corvette engine in their automobiles. Before the Corvette engines were installed the water pump was removed because of a clearance issue with the fan and radiator and the company installed their own water pump. These water pumps had never been run in a car and are 43+ years old. They show the use of the 8-hole hub which started in 1969 on small block and big block engines. Note in the four pictures how the snout of the water pump was masked off and paint runs and because the water pump was on the engine when it was painted note the halo effect of the timing case cover on the back of the water pump. Your comments please. Bill Mock #93
MVC-002S.JPG MVC-003S.JPG

**Joe L.** · November 16, 2013, 12:17 PM

Re: 1970 L46 water pump & pulley?

Originally posted by William Mock (93)

Sirs:[ATTACH=CONFIG]49070[/ATTACH][ATTACH=CONFIG]49073[/ATTACH]
I just purchased a quantity of 3782608 water pumps that came on Corvette engines that were puchased by an automotive company that used the Corvette engine in their automobiles. Before the Corvette engines were installed the water pump was removed because of a clearance issue with the fan and radiator and the company installed their own water pump. These water pumps had never been run in a car and are 43+ years old. They show the use of the 8-hole hub which started in 1969 on small block and big block engines. Note in the four pictures how the snout of the water pump was masked off and paint runs and because the water pump was on the engine when it was painted note the halo effect of the timing case cover on the back of the water pump. Your comments please. Bill Mock #93
[ATTACH=CONFIG]49071[/ATTACH] [ATTACH=CONFIG]49072[/ATTACH]

Bill-----

This pump appears just how I would expect for a '608' waterpump originally installed on an engine. I recall that the rear of the original waterpump installed on my 1969 was painted just about as this one. I do not recall the paint appearance on the front.

The original hub on mine was an "8 holer". The photo below shows the original hub which I re-installed on the pump when I rebuilt it (but, of course, not the original shaft). Ignore the circumferential tape; that's just to keep the protective can (shown in second photo) "tight" on the hub.

One question for you: does the snout on the pump you picture have a pronounced chamfer on the ID at the end. I can't make that out in the photos. Mine has such a chamfer but I don't recall ever seeing another '608' like it. Unfortunately, I can't take a photo of it with the hub installed.

DSCN2916.jpg DSCN2917.jpg

**William M.** · November 16, 2013, 05:10 PM

Re: 1970 L46 water pump & pulley?

Joe, the first picture shows the chamfer that you are talking about. A quick check of my 3782608 water pumps showed that 90%+ had the chamfer. The second picture is the "Almost NOS" "3782608 dated B 10 0 which does not have the chamfer. MVC-006S.JPG MVC-005S.JPGWhat is the casting date on your 1969 3782608 water pump? Bill

**Joe L.** · November 16, 2013, 10:54 PM

Re: 1970 L46 water pump & pulley?

Originally posted by William Mock (93)

Joe, the first picture shows the chamfer that you are talking about. A quick check of my 3782608 water pumps showed that 90%+ had the chamfer. The second picture is the "Almost NOS" "3782608 dated B 10 0 which does not have the chamfer. [ATTACH=CONFIG]49083[/ATTACH][ATTACH=CONFIG]49084[/ATTACH]What is the casting date on your 1969 3782608 water pump? Bill

Bill------

Yes, I have seen many pumps with the sort of chamfer seen in your first photo. The chamfer on my pump is much more pronounced and the face of the snout is machined flat as seen in the pump in your second photo. So, basically, my pump looks like the pump in your second photo with a more pronounced chamfer.

My pump is dated "E 18 9" and was made from foundry pattern number 27. My block casting date is "H 12 9". Heads are "H 11 9" and "H 13 9". Intake manifold is "H 2 9". The engine assembly date is August 14. So, my pump was cast well before the other major cast components of my engine. However, there's absolutely no doubt this is the original pump since I've owned the car since new.

A few other comments on your pump:

I note that it has the original NDH bearing/shaft assembly which is another point of verification that it's an original GM assembly. I have several of these NOS bearing/shaft assemblies but I did not use them to rebuild my pump. Instead, I used an F A G assembly (I also used a John Crane Company mechanical seal assembly with all stainless steel construction, carbon-ceramic seal, and Viton bellows).

I also note that the Chevrolet orange paint color on your pump is EXACTLY what was used at Flint in the 1969-70 period. It has much more red in it than most commercial Chevrolet orange paints of today have in them (the color of the paint on my restored engine is not correct in this context regardless of what Bill Hirsch says).

1970 L46 water pump & pulley?

1970 L46 water pump & pulley?

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