Steam hole difficulty

[USSkoval]

I finally got my 487 heads back from the machine shop and I'm trying to drill the steam holes in them to use on my 400. I can only get 4 of the six holes drilled in each head. When trying to drill the outer holes on the intake side, I get about 1/4 inch in and then the bit goes dull. If I try another bit, it dies too I had no problems drilling the other holes at all. Do I need to go buy some expensive bit or something? The drill bits I have are very strong and I've never killed one until now.

Do I even need to worry about those last holes? The instructions that came with my Edelbrock heads (different project) said to drill the holes on the exhaust side of the head only.

 

[USSkoval]

Any thoughts or suggestions? I'm anxious to get this motor finished and shoved into the truck

 

[Never Satisfied]

Try these links....
http://www.chevelles.com/forums/showthread.php?t=226287&highlight=drill+steam+holes

http://www.gregsengine.com/350to400.htm

The first link one of the guys mentions drilling an angle to miss an area around some of the head bolts. I'm betting that is what you are running into. Hope this helps

 

[Jimbo*]

You are drilling cast iron, it's much more abrasive than steel. Since they are steam holes, I assume they are less than 1/4 inch?
Try a masonry drill bit. It's a non-critical hole, and the masonry bits are carbide tipped, which is designed for abrasive drilling.

 

[USSkoval]

I know about the correct angle to drill the holes, so that's not an issue. I'm just having trouble with two areas in the same spot on each head, where the iron seems to be much harder than everywhere else. It's very weird.