Water pump pulley bolt size?

[TurboTnZ06]

I searched and there are three results, each different. I guess I'll see if these exist and try each one out at the hardware store.

5/16 - 24
5/16 - 25 NF
1/4 - 28

 

[RICHIE HIGH PSI]

5/16-24
Just did mine.

 

[TurboTnZ06]

Thanks!

 

[GNVenom]

METRIC! It's 8mm. x 1.0 with a 13mm hex. They're about 12mm long.


The 5/16NF will not fit properly.

 

[coach]

METRIC! It's 8mm. x 1.0 with a 13mm hex. They're about 12mm long.


The 5/16NF will not fit properly.

You are correct. It is fine thread 8mm. Most 8mm are 1.25 thread. Dont bother looking for stainless bolts. Thye dont make them. The threads are too fine and strip out to easy. I found chrome allen heads at Gardner Wescott.

:biggrin:

 

[TurboTnZ06]

Well, I dug around the garage some more and found a magical box of things I didn't need with the GN1's- stock valve cover bolts, 8445 arp head stud nuts and the water pump pulley bolts which I did need. I also found a new crank sensor, new lt1 maf, and new cam sensor cap! Like Christmas in July!

 

[turbofabricator]

SORRY....They ARE 5/16-24 SAE FINE NOT 8mm metric. 8mm metric might work, but they are all SAE. They are the same pump as long before federally mandated metric rules. Most aftermarket pumps come with studs in the box. Fine thread on one end, course on the other. Even the factory bolts hane the grade 8 stamping on them. If they were metric, they would have a grade 10.9 stamped on them, not the grade8 dashes. Look up bolt identification symbols and you'll see what I mean. Typically, 8mm fine have a 12mm head size. The factory bolts use a 1/2" wrench.

 

[Just a Six??]

SORRY....They ARE 5/16-24 SAE FINE NOT 8mm metric. 8mm metric might work, but they are all SAE. They are the same pump as long before federally mandated metric rules. Most aftermarket pumps come with studs in the box. Fine thread on one end, course on the other. Even the factory bolts hane the grade 8 stamping on them. If they were metric, they would have a grade 10.9 stamped on them, not the grade8 dashes. Look up bolt identification symbols and you'll see what I mean. Typically, 8mm fine have a 12mm head size. The factory bolts use a 1/2" wrench.

Are the pump threads tapered at the end as no matter the size I use on 3 new ones they all get tighter the last 3-4 threads? I always figured they were tapered?

 

[GNVenom]

SORRY....They ARE 5/16-24 SAE FINE NOT 8mm metric. 8mm metric might work, but they are all SAE. They are the same pump as long before federally mandated metric rules. Most aftermarket pumps come with studs in the box. Fine thread on one end, course on the other. Even the factory bolts hane the grade 8 stamping on them. If they were metric, they would have a grade 10.9 stamped on them, not the grade8 dashes. Look up bolt identification symbols and you'll see what I mean. Typically, 8mm fine have a 12mm head size. The factory bolts use a 1/2" wrench.

Turbofabricator is correct - the grade 8 designation are indeed on those bolts. That said, the 5/16-24 and 8mm 1.0 are almost identical and either will work. VERY close to each other in size.

You would need to use 5/16-24 NF grade 8 bolts with a flange - probably impossible to find at a hardware store.

 

[GNVenom]

Are the pump threads tapered at the end as no matter the size I use on 3 new ones they all get tighter the last 3-4 threads? I always figured they were tapered?

They're not tapered. I think you are referring to "distorted thread" screws which have a sort of triangle shape instead of perfectly round.

Tapered threads are only used in pipe applications; the taper gets tighter as you progress the threads. Sort of prevents leaks.

 

[turbofabricator]

Are the pump threads tapered at the end as no matter the size I use on 3 new ones they all get tighter the last 3-4 threads? I always figured they were tapered?

Maybe it's the lock washers you installed under the bolt heads.:biggrin:

Seriously.....not sure I have ever noticed that. I'll think about that next time for sure. GREAT....one more thing to worry about. NO sleep for me tonight.

 

[Just a Six??]

Maybe it's the lock washers you installed under the bolt heads.:biggrin:

Seriously.....not sure I have ever noticed that. I'll think about that next time for sure. GREAT....one more thing to worry about. NO sleep for me tonight.

I notice that the first 5 turns are normal & then if you dont hold the pulley tight or use an impact on low setting they are much tighter that last few turns? I thought it was done on purpose so they wont come loose? Altho, thats purely a Guess on my part?
I have a brand new Delco pump at my friends I still havent picked up & when I finally do I'm really going to check it out. maybe it's just in my head?