Advice for drilling on my intake wanted.

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Troub

67 Dart 270, 225 slant six
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Soooo, I think my replacement exhaust manifold is one where the factory started using a larger bolt to mate the intake and exhaust together. I was trying to check port alignments against the new gasket that came today and the intake would not slide down onto the bolt on the top of the exhaust. I guess I have to enlarge the bolt hole on the intake. Anyone done this and any bit recommendations for drilling that cast iron? Pics...

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Standard black oxide drill bits from Home DePot or Lowe’s... drill slowly, not high speed.
Thanks, should there be any play at all or do I want that drilled out only as wide as necessary to receive that bolt? I don’t know if any play is required at that spot once the intake and exhaust are sandwiched together for flex as they heat and cool. I know that they flex and slide across the face of the head as they heat and cool but wasn’t sure bout movement at this bolt spot.
 
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Any cast iron I've ever fiddle with drills pretty easy....until you break out the other side. Measure carefully, and "break through" gently, or it can break out a big piece
 
I’m not sure on the bolt hole size for the bolt.
Good question
My original exhaust manifolds bolt dropped right into the intake mounting hole, absolutely wasn’t super snug and the bolt diameter is noticeably smaller than the one on the later manifold that I have now. I understand that they went to the larger bolt due to the early size bolts tendency to break off. Anyone out there care to confirm?
 
DON'T just hog it out to the size you want. Use as many bits as you can to remove the smallest amount of metal in between each bit size to work up to your final size.

Use oil.

Slow drill speed, and use light pressure on the drill. It may try to over feed itself so you may have to hold it back as you drill.
 
Measure the dang bolt man. Dial calipers are cheap. Also, I would try to use a drill press so you'll have more support. That way, you can level it up by the hole in the intake and drill it straight.
 
Measure the dang bolt man. Dial calipers are cheap. Also, I would try to use a drill press so you'll have more support. That way, you can level it up by the hole in the intake and drill it straight.
Lol I know the bolt size. My question was whether or not mother Mopar had the hole much bigger than the bolt to allow for play?
 
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Lol I know the bolt size. My question was whether or not mother Mopar had the hole much bigger than the bolt to allow for play?
Early years had a smaller bolt hole on the intake later had bigger ones. Due to different bolt sizes
 
Any cast iron I've ever fiddle with drills pretty easy....until you break out the other side. Measure carefully, and "break through" gently, or it can break out a big piece
That's an easy one, pre-drill/chamfer the other side of the hole, then drill through from the intended end........as stated,....cast drills relatively easy
 
I used my el-cheapo drill press & 3 different drill sizes to slowly step up to the new size hole.
 
I tried to open up the big hole for the head pipe on a exhaust manifold with a bur and die grinder. Same bur I used to port the head. I gave up! :(
Yeah, the exhaust alloy is more difficult, but fresh carbide still works, I ported a set of mid-'70's 440 units. It does go sloooow tho',.......
 
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