Anyone know what bit these water pump pulley bolts are? (CAXC)

[Rakhsh]

Hi everyone. I'm doing the timing chain and decided to do the water pump too while I'm here since the pulley needs to come off for the timing chain cover to be removed anyway. I'm stuck on these water pump pulley bolts:

There's not enough clearance for me to put my regular M10 triple square socket on it but I did try my stubby M10 triple square and it was slightly too big. It would "fit" but wouldn't go in much at all and turning it would just result in it coming loose.

I tried a T50 torx too before I realised it was a spline screw, this one would go in but was obviously too small and not the right shape. Anyway, can anyone confirm these are actually M10? I saw on a YouTube video that the guy used an M10 bit but no other videos said how they got this off. I have ordered a new M10 bit (just the bit, no holder) from Amazon (Draper brand) and it arrives tomorrow so I'm hoping that will fit.

M8 is far too small. I don't think an M9 exists does it? Would be a very weird choice by VW to put it on here anyway.

Also does anyone know if I need to replace these bolts? I assume not because my new water pump didn't come with any. Thanks.

 

[RUM4MO]

Parts listing quotes "M8 X 12 Socket head collared bolt with inner multipoint head " for that bolt, part number N 910 522 01 - so I'd expect that it has an M8 multi spline pattern on its head.

Edit:- if you bought a new bolt you'd be in a better position to work out if it is an "M8" triple square or even an "M9" - US Pro/Berlin do sell an "M9" multi spline bit - if that is what you end up needing.

 

[Rakhsh]

Weird. Maybe previous owner replaced it for something different because both my M8 spline bits are too small. My new M10 should arrive in the next few hours though so I'll see if it was just my cheap Amazon bit being a little bigger than it should be.

 

[Rakhsh]

My new M10 bit arrived and it fit perfectly fine. My old one must've been bad.

And pro tip for stopping the pulley from spinning: use one of those rubber oil filter wrenches to hold it in place.

You can try to undo them with the serpentine belt on but when I tried to do that it would just turn the crank because these bolts are normal threaded not reverse.

 

[RUM4MO]

I thought that you might be able to use the existing belt and clamp it using vise grips or similar - to do the same job as your "rubber oil filter wrench" - I've got a pair of these rubber band wrenches, the original BOA-CONSTRICTOR version - very useful, even to open jars! (and plastic plumbing fittings)

Going back to you finding out that the bolt head insert is M10 while the bolt thread is M8, I'd think that when VW Group came up with that bolt, it would have had the right to make the "head - tool" size what they felt was most suited to that bolt - so that should explain why it is M10 multispline.

 

[Rakhsh]

Honestly I have no idea what the real name of this thing is but I got a 2 pack for £5 and I'm sure it'll be helpful for all sorts of things. You could definitely do the vice grips thing but I'd imagine it would not be as convenient to hold since the wrench thing has a nice handle you can apply pressure to to hold it against whatever it is, vice grips would probably be awkward.

Also really odd that spline bits are named the same way as bolts. Why would they name it M10, it will just get confused for bolt sizes.