Water Pump Bolts??

[John L.]

I have a 68 corvette 427 with water pump 3858284, The water pump was rebuilt and has slotted pan screws holding the back cover. Would this be correct? I thought the cover should be held on with hex head screws stamped "L". I need to paint the water pump so I need someone with a 68 427 to answer my question soon.

Thanks!

John................

[Rich P.]

Re: Water Pump Bolts??

John,

You are correct 65 BB and early 66 (I think) had the slotted screws your 68 needs the Hex bolts w/star washers.

Rich

[Jack H.]

Re: Water Pump Bolts??

Also, the slot-head screws were 'typically' used with the flat rear plate while the hex-head bolts are ususally seen on stamped rear plates (plate has an outside 'lip' that serves to strengthen it and add rigidity). I'd suspect that by '68 all BB water pumps had the later era construction with stamped/lipped rear plate and hex-head bolts...

[Mark F.]

Re: Water Pump Bolts??

Here is a photo of the hex head bolt and star washer. This is from a C 7 8 dated 284 water pump. The markings on the head of the bolt say "B&H". It also has the lip on the edge. I also have another 284 water pump that the hex bolts have what looks like a wavy banner. It has the flat backing plate. It's dated I 12 7. Maybe someone can comment more on the proper bolt markings.

Mark

[John L.]

Re: Water Pump Bolts??

Thanks for the fast reply. My water pump has the back plate with the lip. I suspect someone couldn't fit the pump on the block with hex head srews because they touch the timing cover so they used the slotted screws. I will try replacing the slotted screws however two would need to be filed down for clearance. It's posible that when the pump was rebuilt, someone may have ground too much matterial off the matting surfaces in order to clean them up.

John.......................

[Joe L.]

Re: Water Pump Bolts??

Thanks for the fast reply. My water pump has the back plate with the lip. I suspect someone couldn't fit the pump on the block with hex head srews because they touch the timing cover so they used the slotted screws. I will try replacing the slotted screws however two would need to be filed down for clearance. It's posible that when the pump was rebuilt, someone may have ground too much matterial off the matting surfaces in order to clean them up.

John.......................

John-----

I believe that GM changed the design of the waterpump rear plate due to sealing problems with the original "flat" design. When this change was made, the change was also made to hex head bolts since, due to the reinforcing lip's configuration, the extra height of the bolts was pretty much moot.

However, while this change may have done a lot for pump sealing, it caused problems with water pump-to-timing cover interference. These problems plagued both small block and big block applications.

Chevrolet solved the problem once-and-for-all in 1969 when the change was made to the "long leg" style waterpump for most Chevrolet V-8 applications. However, the "most" did not include Corvette and MD/HD trucks. So, they continued to suffer with interference problems.

[Rich P.]

Re: Water Pump Bolts??

Here is a photo of the hex head bolt and star washer. This is from a C 7 8 dated 284 water pump. The markings on the head of the bolt say "B&H". It also has the lip on the edge. I also have another 284 water pump that the hex bolts have what looks like a wavy banner. It has the flat backing plate. It's dated I 12 7. Maybe someone can comment more on the proper bolt markings.

Mark

Mark,

both the B&H and the FLAG or as you call it wavy banner are period correct for 68.

Rich

[John L.]

Re: Water Pump Bolts??

Joe Lucia, thanks for your reply. Now I understand, it's a design problem.

Take care,

JL

[Jack H.]

Re: Water Pump Bolts??

I'm not sure I'd call it a 'design problem'... A better terminology might be 'issue' or 'design improvement'.

LOTS of cars went out the door with flat water pump rear plates + low profile slot head screws and GM didn't 'collapse' from excessive warranty claims! It's simply what Joe said, the 'ribbed' or 'stamped' or 'lipped' rear plate provided superior rigidity and sealing qualities.

Then, once you had the extra height of the rear plate's 'lip' on the back of the pump, why use slot head screws? Hex head bolts are MUCH easier to work with given the use of pneumatic assembly tools...

[Joe L.]

Re: Water Pump Bolts??

I'm not sure I'd call it a 'design problem'... A better terminology might be 'issue' or 'design improvement'.

LOTS of cars went out the door with flat water pump rear plates + low profile slot head screws and GM didn't 'collapse' from excessive warranty claims! It's simply what Joe said, the 'ribbed' or 'stamped' or 'lipped' rear plate provided superior rigidity and sealing qualities.

Then, once you had the extra height of the rear plate's 'lip' on the back of the pump, why use slot head screws? Hex head bolts are MUCH easier to work with given the use of pneumatic assembly tools...

Jack-----


A lot had to do with the cooling system pressure. When the pressure was 7 PSI, the flat plates worked ok. When they went to 13 PSI, the flat plate was marginal. At 15 PSI, it was "hit-or-miss".

I did some tests with waterpumps using the flat plate, lipped plate without impressed ridges, and lipped plate with impressed ridges. I carefully installed the rear plates on the pump, used sealer on both sides of the gasket (which the factory did not), and carefully cross-torqued the bolts to the top of the torque range.

I was not able to achieve sealing with the flat plate at 15 PSI. Even the lipped plate without impressed ridges was very marginal at 15 PSI. When I got the pressure just slightly above 15 PSI, it leaked.