Need Help on Bolt Size
 

Hey guys, I've been searching all over the net today and can't seem to find it anywhere! What size are the bolts that hold the mechanical fan to the water pump? Essentially, what size bolt goes into the pump through the pulley? My truck didn't have any of this installed when i got it, and even though I am swapping to an electric fan, I still need the pulley attached!

Oh yeah, it is a 1957 3100, with the "assumed" original motor, a 235.

Re: Need Help on Bolt Size
 

They should be 1/4"x3/4" with a lock washer. As far as I remember the older pumps used a coarse thread but not positive

Re: Need Help on Bolt Size
 

Any of the ones I've done, mostly V-8's use a 5/16 NF(24) on that water pump flange. That and the crank pulley to balancer are the few fine thread bolts on that vehicle.

Re: Need Help on Bolt Size
 

On a 235 the bolts will be fine thread.

Re: Need Help on Bolt Size
 

Yes, I've never seen a small block pump with anything else.

I've never seen one with 1/4 inch bolt holes either.


In case you can't eyeball a bolt and tell it's diameter, outside of a few odd ball bolts the following almost always holds true.

1/4 inch bolt = 7/16 wrench
5/16 inch bolt = 1/2 wrench
3/8 inch bolt = 9/16 wrench
7/16 inch bolt = 5/8 wrench but often has a nut that takes a 11/16 nut.
1/2 inch bolt = 3/4 wrench

The larger sizes can be mix and match so I left them out.

Re: Need Help on Bolt Size
 

My mistake. Yes 5/16

Re: Need Help on Bolt Size
 

So just to clarify, as it looks like we may have gotten off track as far as the v8's go, (sorry, I may be misunderstanding) on my 235 straight 6, The bolt that goes into the water pump pulley is a 5/16 fine thread? Just want to be sure as I have nothing to go off of right now - nothing there. I would really like to get the truck going with the cooling system working so that I can run it for longer than 3 minutes without cooking anything! Thanks for the help guys!

Re: Need Help on Bolt Size
 

you could run a tap in the hole and get the fit, you should be able to do this with out a wrench so as to not cut a differant thread. startwith a fine thread tap, this works for me good luck.

Re: Need Help on Bolt Size
 

Most studs have a fine and a course thread side. you should be able screw the correct threaded stud or bolt in with your fingers.

You could use a tap to clean the threads if they have rusted for some reason but usually you don't need to do that.