Mark IV Big Block Oil Pumps

[Joe L.]

I recently learned something about the above-referenced that I was not heretofore aware of. I was always of the understanding that the only Mark IV big block that used a high volume oil pump was the 1969 ZL-1. However, that's not how it was. As it turns out, 1965-66 also used an oil pump that could be essentially described as "high volume".

Thanks to George Wright I was able to obtain a 1965-66 oil pump for "autopsy". As folks may be aware, "standard" volume Mark IV oil pumps used gears that were 1.15" overall length. The 1969 ZL-1 high volume pump used gears that were 1.38" OL. However, as it turns out the 1965-66 big block pump used gears that were 1.30" long. That should produce a volume about 13% greater than the 1.15" gear pumps. All 1967-74 Mark IV pumps, except ZL-1, used the 1.15" gear pumps. All 1965-74 pumps use the same OD gears at 1.773". The internal machined cavity dimensions are, as close as I can measure them, the same for both pumps.

We do not know the complete history of the 65-66 pump which I "autopsied" except that it is a 1965-66 pump. It currently appears to have the high pressure spring installed but that may or may not be what was originally installed in the pump. Also, it has a pick-up installed which is definitely not Corvette since the tube section is much longer than Corvette.

Attached are photos of the internals of the 1965-66 pump and an NOS GM #3904826 pump which was the 1967-71 SHP pump as well as the SERVICE replacement for the 1965-66 SHP pump after December, 1966. The 65-66 is on the left side of each photo and the NOS 3904826 on the right.

So, why the higher volume pump for 1965-66? Well, I expect it had something to do with the unique-to-65/66 oiling system. However, GM must have considered that the "standard volume" 67+ pump would work just as well (or better) because they replaced the 1.30" gear pump with 1.15" for SERVICE.

[Joe L.]

Re: Mark IV Big Block Oil Pumps

Some more photos the the 65/66 and 3904826. Note that this example of the 3904826 was actually cast at Tonawanda as evidenced by the "GMT" casting mark.

[Joe L.]

Re: Mark IV Big Block Oil Pumps

Note that the installed pick-up on the "autopsied" 65/66 pump is not Corvette by comparing to the NOS 1965-66 Corvette pick-up.

[Joe L.]

Re: Mark IV Big Block Oil Pumps

Note that the cover for the 3904826 pump (purple dye mark) was also cast at Tonawanda (note the "T" casting mark).

[Timothy B.]

Re: Mark IV Big Block Oil Pumps

Joe,

Thanks for posting your findings about the gear height for 65-66 big block. It's also interesting how the idler pin is lubed by the groove in the cap. I know there are others that will be interested in this information.

That original looks like it's in nice condition.

[Patrick B.]

Re: Mark IV Big Block Oil Pumps

Joe:
The oil pump that I think came out of my 69 ZL-1 looks a whole lot like the 66 pump in your thread but the body casting number is different. It body casting is 3863688 or 698 (the numbers are very hard to read); the lid casting is 3860376 same as yours. The gears are 1.30" and a Corvette pickup screen was tack welded on. The old Chevy power books list the ZL-1 pump as 3969870 with 1.30" (not 1.38") gears and a welded on screen.

[Michael H.]

Re: Mark IV Big Block Oil Pumps

I recently learned something about the above-referenced that I was not heretofore aware of. I was always of the understanding that the only Mark IV big block that used a high volume oil pump was the 1969 ZL-1. However, that's not how it was. As it turns out, 1965-66 also used an oil pump that could be essentially described as "high volume".

.

Joe,

I think the pump that you show is actually a service only drag race pump for 65-66 passenger cars. It goes along with the special service only deep sump 7 (?) qt oil pan.

The oil pump part number is 3879643.

The special oil pan is part number 3879633.

If I remember correctly, the oil pump included the special long oil pick up tube/screen.

[Joe L.]

Re: Mark IV Big Block Oil Pumps

Joe:
The oil pump that I think came out of my 69 ZL-1 looks a whole lot like the 66 pump in your thread but the body casting number is different. It body casting is 3863688 or 698 (the numbers are very hard to read); the lid casting is 3860376 same as yours. The gears are 1.30" and a Corvette pickup screen was tack welded on. The old Chevy power books list the ZL-1 pump as 3969870 with 1.30" (not 1.38") gears and a welded on screen.

Patrick-----


I'm not surprised the original 3969870 pump had 1.30" gears. However, I have a later-manufactured 3969870. By the time that pump was manufactured I think that Melling had been selected as the manufacturing vendor to GM. The gears in the 3969870 pumps I have are 1.38" overall length. It does have the welded-on screen, too.

[Joe L.]

Re: Mark IV Big Block Oil Pumps

Joe,

I think the pump that you show is actually a service only drag race pump for 65-66 passenger cars. It goes along with the special service only deep sump 7 (?) qt oil pan.

The oil pump part number is 3879643.

The special oil pan is part number 3879633.

If I remember correctly, the oil pump included the special long oil pick up tube/screen.

Michael------


That could very well be and makes sense. The pick-up screen on this pump does not appear like any PRODUCTION piece I have seen. However, the pump body and cover are the same casting numbers as the PRODUCTION 65-66 oil pump. So, I would expect that the only difference between the 3879643 and the PRODUCTION pump was the welded-on oil pump pick-up screen. The PRODUCTION and SERVICE pumps were not supplied with a pick-up screen (except ZL-1, L-88, and some truck pumps).

[Clem Z.]

Re: Mark IV Big Block Oil Pumps

michael is correct as i used those pump and deep pan on drag race engines. the pick up was welded to the pump as delivered. i was under the impression the setup was originally used in heavy duty trucks. i even used this setup on some circle track engines where ground clearance was not a problem.

[Clem Z.]

Re: Mark IV Big Block Oil Pumps

michael is correct as i used those pump and deep pan on drag race engines. the pick up was welded to the pump as delivered. i was under the impression the setup was originally used in heavy duty trucks. i even used this setup on some circle track engines where ground clearance was not a problem.

if i remember correcty those pans were sectioned and the sump was deepened by adding a welded on piece to make it deeper. i may have one around here somewhere.

[Clem Z.]

Re: Mark IV Big Block Oil Pumps

as far as the length of the gears it could have been the length used in the 409/427 "W" which the mark IV was based off of as a mark IV crank can be installed in a 409

[Patrick B.]

Re: Mark IV Big Block Oil Pumps

Mark Nagy, one of this group's contributors, told me the original oil pump in his 66 427-425 had the casting number 3860370 and 1.30" gears. I think Joe had it nailed from the beginning. This was a production pump for 66 SHP big blocks. Maybe Mark will chime in. Melling apparenty tested his pump recently and was quite impressed with it.

[Joe L.]

Re: Mark IV Big Block Oil Pumps

as far as the length of the gears it could have been the length used in the 409/427 "W" which the mark IV was based off of as a mark IV crank can be installed in a 409

clem-----


The 409 used the same oil pumps as small block Chevrolets.

[Clem Z.]

Re: Mark IV Big Block Oil Pumps

clem-----


The 409 used the same oil pumps as small block Chevrolets.

what about the Z-11 ???