C2 "326" water pumps.

[Clark D.]

This winter a friend and I decide to each replace the generic water pumps in our C2s with the correct "326" water pumps. I have a 66 350hp and he has a 65 365hp. Actually this has turned into quite a challenge. To date I have ordered and recieved two 326 water pumps from LIC and the flanges were about an eight of an inch short in attaching to the block, on each engine, both pumps. The pumps hit the timing chain cover first and will not mate. I then ordered a repop 326 from Ecklers and it had the same problem. My friend bought a rebuilt 326 off ebay and it exhibited the same problem on both engines. We do have one 326 core that we sent back to Arthur Gould for rebuild that fits perfectly. The only thing we can think of: The pumps have been milled so much over the course of rebuilds. However an eight of an inch is quite drastic. This also would not explain the repop water pump.

Any thoughts here?
Clark #42490

[Rob A.]

Re: C2 "326" water pumps.

Clark,

I bought an original,dated 326 pump for my '66 L79. I haven't tried to install it yet, but now you have me wondering if I will run into any problems. Do you think I can tell by taking some measurements first? I'll be curious to see the responses you get.

[Jack H.]

Re: C2 "326" water pumps.

These interference fit problems are typically the result of water pump rebuilder ignorance... Early water pumps (prior to '326 casting), used a flat rear plate with low profile slot head screws to supply ample pump to timing cover clearance.

Then, technology 'improved' and the a rear plate with a rolled stamped reinforcing edge was introduced for better rigidity/seal. It's unclear from our JG books just when the stamped rear plate entered the picture, but on BB water pumps the JG books document continued use of the flat rear plate into the '66-67 era. Of course, these pumps were different and products of Tonawanda vs. Saginaw/Flint.

Now, when the stamped rear plate came along, it was typically installed with low profile, hex bolts to gain/preserve as much clearance as possible between the rear of the water pump and the timing cover. Rebuilders that 'blindly' install fresh rear plate bolts using off-the-shelf 'hardware store' fasteners wind up with the heads of the bolts extending too far rearward.

Savvy judges will frequently shine a flashlight between the rear of the water pump and the front of the block to see which style rear plate has been used on the pump + which form of rear plate is installed...

Bottom line: there's more to getting a 'correct' water pump than simply buying one with a 'correct' casting number/casting date!

[Clark D.]

Re: C2 "326" water pumps.

Jack;

Initially, I thought the rear plate was the issue. I took the rear plate off a water pump that fit properly and moved it over to the 326 that didn't fit. I still had the interference issues. That is why I am still perplexed over the issue. Thanks for the input.

[Wayne M.]

Flat metal backing plate -- 284 BB pump

Here's the plate on a big block water pump 3856284 of May 5th 1965 cast, showing the plate and panhead screws that Jack describes. I would assume that this plate configuration was also used on all small block pumps of that era, although I've not seen any. If you look closely you can see the "points" of the star washers under the screws.

The '65 TM & JG just refers to backing plates that are "stamped metal" without the "flat" descriptor.

Before I send this pump out for rebuild, I will remove the plate and screws/washers.

[Joe L.]

Re: C2 "326" water pumps.

Clark-----

I doubt that the waterpump block mating surfaces have been milled; I've never known rebuilders to do this. I think that they would just discard a core if this needed to be done for exactly the reason that your problems suggest.

Anyway, here are the specs for the dimension from the waterpump-to-block mounting bolt seat to the block mating surface for all 4 waterpump mating surfaces. These dimensions originate from GM specs and I've CONFIRMED them by measuring the dimensions on a brand new, NOS GM waterpump using the '326' casting. To avoid confusion, I'll use driver and passenger side as the pump is mounted on the car to describe each position:

top, driver side----0.902"

lower, driver side---1.140"

top, passenger side---1.105"

lower, passenger side---2.00"

Also, you need to check the dimension of the plane of the rear plate mounting surface to the plane of the block mounting surface. To do this, place the pump on a flat surface with the "legs" sitting on the flat surface. Measure the distance form the flat surface to the rear plate mounting surface. It should be right at 1.22".

Report what you find on the above dimensions.

Another possible problem: are you sure that the timing covers on the engines are original? Do you know if the timing covers have ever been off the engines and, possibly, thicker-than-stock timing cover gaskets used? Are the timing covers in any way distorted?