Water pump weird bolt

Trying to change my water pump and came across this weird little bugger
Anyone seen this ? All other bolts are half inch hex.

Assuming this is from a V12:


"Some, but apparently not all, water pumps have a single countersunk Phillips screw. According to Thomas Alberts, it is a common mistake to overtighten this screw, resulting in a fracture of the aluminum casting surrounding it. Apparently the casting was designed for a non-countersunk bolt, and adding the countersinking makes the metal too thin for serious tightening. If you wanna make sure the pump doesn’t leak, use a good sealing compound, don’t overtighten this bolt.:

The JDHT website gives this screw is item #17 ( SF505101J):

The screw pictured is a Posidrive.

Thank you for that I think I need to go shopping for a Phillips head bit that will fit that I think I have one chance to get that thing out and I don’t have any bits that seem to fit properly

Thank you for pointing it out. Clearly it is NOT Phillips, but I am not the one who wrote the paragraph.
I also provided the correct part. # and any reference to it ( SF505101J) is PZ

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I didn’t mean to imply you didn’t know the difference.

Many people can’t tell the difference, and end up buggering the heads up. It’s one thing when it’s on a doorcatch, or hinge… completely different when it’s a struggle to get at, so I thought I’d shout a warning.

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Look at your new water pump and see if that screw/bolt hole is recessed or not.
If it was like the new one I bought, it wasn’t.

The weird screw/bolt will still clear the belts however if I had to do it again I would have tapered the hole in the pump so that it would seat better.

So this looks to be something they did on going with the wide serpentine type belt on the alternator versus the V belt because my 87 I did a water pump on didn’t have this issue and it had a V-belt alternator instead of the flat serpentine type
Anyway I need to seek out correct Posi Drive bit
Thank you everyone for your help

#4 Posidrive (#3 might be too small) bolt on water pumps from engine number 86249 (I think?) has the countersunk bolt.

Been a long time since I replaced one.

One option is to buy a nut driver kit with all types of screwdriver tips, star driver tips,etc
The kit I have included # 1, 2, 3, and 4 Posidrive tips. Got mine from Griots Garage … good quality. No affiliation. I think Harbor Freight has similar kits. Very handy.

Aye, mine came from HF. Very useful. Has tips I use and others that Inever have and probably never will. I think HF termed mine as a Security something.

Lots of Pozi on these cars.


Interesting thing is after reading about not over tightening and such that my “new” water pump has what looks like some welding repair in the area of the PoziDriv bolt. Guess I best be cautious here.

I will try to find the correct bit today.

Thanks again all. I should have known “the book” would mention it.

I also have that Harbor Freight kit and in addition to the Pozidrive bits I have found the Torx bits useful for the fasteners on the seat mounts and door latches. I probably haven’t used 90% of the wide variety of different fasteners in that kit, but there are a bunch that I use all the time. Especially the Pozidrive ones.