Drill AFR 165 heads for 1/2" studs - Ford Muscle Forums : Ford Muscle Cars Tech Forum
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post #1 of 3 (permalink) Old 03-09-2014, 11:20 PM Thread Starter
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Drill AFR 165 heads for 1/2" studs

Has anyone enlarged the head bolt size on their AFR 165 heads from 7/16" to 1/2"?
I have a ford R-block(1/2" head bolt threads) 331 that I am scaling down to a milder setup.
I took off my AFR 205s and thought my 165 were 1/2". Ooops.
I found one thread about somebody asking if they could do this, and as usual there was no closure on the thread.

I will talk to my machine shop tomorrow about this.
If I had to do it myself, I would true up my drill press and first use a step drill that has a 7/16" to 1/2" step. Then I would use a 1/2" drill to drill thru the head and open the hole up. I would finish with a 17/32nd drill bit and go thru again.
The idea is that the step bit starts the hole true to the 7/16" hole. The 1/2" uses that hole to start straight. The 17/32" is what the holes in my heads that use 1/2" bolts/studs are actually. So I would give a pass to clean up down the 1/2" hole and all should be good if everything stayed true.

Perhaps I should skip the 1/2 and go straight to the 17/32?


Any thoughts.

The thread I was looking at made this sound like it should be easy.
It scares me to take my expensive heads and chop like this.

This motor is going into a 62 Jaguar MK2 with a tremec 5spd.
It should be fun and a real sleeper. Car will be just under 3000 pounds.

63.5 Galaxie 500. Outa this world!

Last edited by selash; 03-09-2014 at 11:22 PM.
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post #2 of 3 (permalink) Old 03-10-2014, 04:07 AM
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Re: Drill AFR 165 heads for 1/2" studs

I drilled a set of 289 heads out for 1/2" head bolts. At first, I used a 1/2" drill, but it was too tight. I ended up using a 33/64" drill, and it worked fine. Could have used a more common 17/32" though. I would strongly recommend using a drill press in order to drill the holes straight. Make sure everything is level and perpendicular, as it wouldn't be too hard to drill those long top holes crooked. 17/32" should give you plenty of cushion, though. I may have gone in steps... but don't remember exactly.

Good Luck!

Last edited by n2omike; 03-10-2014 at 04:10 AM.
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post #3 of 3 (permalink) Old 03-10-2014, 04:12 AM
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Re: Drill AFR 165 heads for 1/2" studs

Sounds to me like you got the equipment and have it all figured out. Should be easy since the "pilot holes" are already there and straight. Ensure the bits are sharp, use lots of lube, and take your time. Want the bit to cut but not grab. I'd clamp the head to the table too since you are in the large bit range. Just remember that you need to drill 20 holes total so don't get sloppy.

Would be a breeze on a Bridgeport though once the head was first setup on the table.


65' Stang Street/Strip. Dart 434W NA, Victor heads, G101A 4 Spd, 4:56 rear gear, on 93 octane pushing 3550lbs. [email protected]
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