Water Pump Housing Bolt Size

[Gray035]

I have a Mercruiser Alpha I Gen II and I need to tap one of the bolt holes for the water impeller housing. Does anyone know the bolt size so I can get the correct tap? I have a thread gauge (but it doesn't include all sizes), but those bolts don't seem to match anything on the gauge I have.

Also, do the nylock nuts used for attaching to upper unit to the lower unit need to be replaced every time the lower is separated?

Any help would be much appreciated.

 

[Fun Times]

Here's some info on the screw,

--SCREW, (M6 x 16)

https://www.mercruiserparts.com/816928-screw
Usually you won't need new bolts or nuts for the upper and lower mounting the first few times that is unless the nylock nut plastic material inside the nut is worn out to where the nut turns to easy then it's a good idea to by new OEM nuts from Mercuiser as they are special type material nuts.

 

[harringtondav]

Agree with ^^. Nylocs aren't as important as achieving the correct torque. I replaced bell hsg nuts once, for cosmetic reasons. Every other lock nut in my drive is 23 yrs old, disassembled several times. And always tight when removed.

 

[Fun Times]

Screw is item number 26, https://www.mercruiserparts.com/bam/subassembly/30858/1017/80

 

[Gray035]

So I see that the bolt is an M6 x 16. I discovered that there are a couple types of thread for M6 bolts - M6-1.0; M6-0.75 etc. Does anyone happen to know which thread type I need? If no, I might just get both taps from Grainger and send the wrong one back.

 

[Bt Doctur]

Pretty sure its the M6-1.0

 

[harringtondav]

Take one of your old screws to the hardware store and test fit with an M6 nut until you find your pitch Also, must get SS.