I would like to enlarge a 5/8 inch hole in a billet aluminum pulley and pulley spacers to 3/4 inch. If I get a good quality 3/4" bit and enlarge the hole on a drill press, am I risking a centering issue with the pulley on the shaft? Is there one special drill bit that works better than another? Am I better off having a machine shop do it?  This is the dual belt project on my Y blocks with using the double groove dampner with double groove alternator pulley and getting a water pump pulley that will work. I have a drill press.

Darrell Howard Whitefish, MT Outlaw 56 Ford F-100's

The 3\4" drill bit is going to give you a hole that is a few thousandths larger than the stated size.If that isnt a problem you will need to be very careful about center and be sure your pulley is secured in the drill press so that it cannot move! I usually do this sort of work in the lathe but I reckon it could be done in a good,stout drill press?

Do I need to buy a drill bit that is under 3/4"?

Darrell Howard Whitefish, MT Outlaw 56 Ford F-100's

Darrell

If you use an undersize drill and then Ream it to the size you need, it should work ( if the part DOES NOT MOVE in the drill press. You must have it centered, a last word indicator would be the best choice to center the hole on the press, You might save yourself time and money by using a machine shop to enlarge it for you.

Gary Ryan San Antonio.TX.

I've done this using a step drill and haven't had any problems. Each step sort of stops before cutting again. Chuck

Y's guys rule!
Looking for McCullouch VS57 brackets and parts. Also looking for 28 Chrysler series 72 parts. And early Hemi parts.

MoonShadow, 292 w/McCulloch, 28 Chrysler Roadster, 354 Hemi)
Manchester, New Hampshire

You should get it close enough with a drill press if you set it up carefully.  You can use a 5/8" bit to line it up and then install a 3/4" bit to drill.  You can also use the taper of the 3/4" drill to align it.  Pull the bit down os it touches the pulley and turn it backwards a couple revolutions by hand to align it.



Lawrenceville, GA

Enlisting a machine shop with an engine lathe to drill or bore the pulley hole undersize and then ream the hole to final size is the way I would approach this.  Even if the machine shop only uses a three jaw chuck to hold the pulley, I'd have more confidence in getting the hole centered than depending on a reliable drill press set-up.
No keyway, Darrell?Regards,

NoShortcuts
a.k.a. Charlie Brown
near Syracuse, New York

Charlie,

No keyway. This is the fan pulley not the dampner. The fan pully also includes a set of spacers which have to be enlarged from 5/8 to 3/4. Not sure I understand what you mean by "no keyway". I tend to think the machine shop is a good idea, but its not certian it will work until I can test it. Its like throwing a $100 bill (plus the cost of the machining) out on the crap table. Im already nervous about gambling the cost of the pulley and spacers, but then to add more to the cost using a maching shop to enlarge the whole just increases my loss if it dont work. The good news is if it works, I can at least let others know what components I have and what worked for me. If someone wants to double belt a dampner, water pump, and alternator, I will know what works (or does not work). Obviously double belting also opens up other windows for air compressor and power steering.

Darrell Howard Whitefish, MT Outlaw 56 Ford F-100's

It seems to me, a non anal type, that the center hole isn't that important. The pulley is drawn tight by the 4 bolts that are on a set diameter. I've used pulleys with oversize center holes and re-drilled some and never had a problem. At least not one that I could see. I would think if the center hole was a little off it would be quite apparent in the fan rotation. Anyway, that's my take on the problem. Not saying I'm right, just what I've seen. But again, I don't think like a machinist or engineer. Chuck

Y's guys rule!
Looking for McCullouch VS57 brackets and parts. Also looking for 28 Chrysler series 72 parts. And early Hemi parts.

MoonShadow, 292 w/McCulloch, 28 Chrysler Roadster, 354 Hemi)
Manchester, New Hampshire

Remember, the front spacer has to have a pilot to center the fan blade.  If you just bore the spacer to 3/4 then you won't have that pilot.  Unless your water pump has a fan mount included in the casting that you need, why not just put a 5/8 shaft water pump on it?

John - "The Hoosier Hurricane"