size of drill bit & tap for crank snout

[Al R.]

Hi All, I've searched the archives w/o success. What size drill bit & tap does one use to tap & thread the crank snout for the balancer bolt? Also, any helpful tips would be appreciated. Engine is out of the car and on an engine stand, so access is easy. TIA Al

[Doug F.]

Re: size of drill bit & tap for crank snout

we use 7/16 x 20 bolts in our cranks so the tap size we use is 25/64 ths, make sure you get the hole drilled straight or you will not be happy with the results

[Joe L.]

Re: size of drill bit & tap for crank snout

we use 7/16 x 20 bolts in our cranks so the tap size we use is 25/64 ths, make sure you get the hole drilled straight or you will not be happy with the results

Doug-----


With the crank installed in the engine, getting the hole drilled straight is tough. However, getting it TAPPED straight is even much more difficult.

[Al R.]

Re: size of drill bit & tap for crank snout

anyone ever made a type of homemade jig to help keep the bit straight??

[John H.]

Re: size of drill bit & tap for crank snout

anyone ever made a type of homemade jig to help keep the bit straight??

Al -

Note that it's 7/16"-20 for small-blocks, and 1/2"-20 for big-blocks; 1/2"-20 takes a 29/64" tap drill.

[Al R.]

Re: size of drill bit & tap for crank snout

Thanks John, any tips on keeping proper alignment. I've thought about putting a level across the top of the block to level long ways, but unsure how to keep the drill level

[Clem Z.]

Re: size of drill bit & tap for crank snout

Thanks John, any tips on keeping proper alignment. I've thought about putting a level across the top of the block to level long ways, but unsure how to keep the drill level

if you have a friend with a machine shop have him make you a drill jig to slip fit over the crank snout with a pilot hole on the end to align the drill and then the tap

[Joe L.]

Re: size of drill bit & tap for crank snout

if you have a friend with a machine shop have him make you a drill jig to slip fit over the crank snout with a pilot hole on the end to align the drill and then the tap

clem-----


That's a great idea. The tool could be modeled after and, perhaps, partially fabricated from one of those crank turning tools which slip over the crank snout.

[Clem Z.]

Re: size of drill bit & tap for crank snout

make a drill jig like this.

[Al R.]

Re: size of drill bit & tap for crank snout

Thanks all for the responses. I'll try to contact a machine shop on the suggestions.

[Bill H.]

Re: size of drill bit & tap for crank snout

Thanks John, any tips on keeping proper alignment. I've thought about putting a level across the top of the block to level long ways, but unsure how to keep the drill level

My Ryobi drill has levels built into the top of it.

I do like Clem's jig and realize that you need to protect the crank but if it was me. I'd use an easyout, PB Blaster and some heat. Just did 3 bolts on my 67 this way yesterday.
And, if you can pull out the broken piece, i wouldn't use a thread tap, I use a rethread "tap".

But do it the way that makes you feel comfortable.

[Clem Z.]

Re: size of drill bit & tap for crank snout

i was under the impression he was starting with a undrilled crank

[Bill H.]

Re: size of drill bit & tap for crank snout

i was under the impression he was starting with a undrilled crank

Proly, my mistake Clem.

[Thomas N.]

Re: size of drill bit & tap for crank snout

I made one of these tap guides to clean out a broken crank snout bolt for a neighbor in his sbc. I'm pretty sure I've got it in my toolbox. If you are interested, I can find it and drop it in the mail to you.

[Al R.]

Re: size of drill bit & tap for crank snout

Thanks anyway Thomas, someone is sending me one to use and return. Appreciate the offer, though. Al