decking the head?
01-07-2012, 07:23 PM
#31
6th Gear Member
Join Date: Feb 2007
Location: state of confusion
Posts: 7,635
I've hand-tapped a few things, but nothing as angularity-critical as rocker stud holes. It's way too hard to keep the tap straight and once it's started to cut crooked you've lost that battle (and may even break the tap off leaving a piece that's too hard to drill out stuck there in the hole). Don't do it.
Fitting the biggest possible valves can end up costing you power due to shrouding on the chamber wall side. A streetable 289/302 simply does not need 2.02's.
Building up your engine should be about putting together a good combination of parts. Not about individual spec numbers themselves.
Norm
01-08-2012, 10:04 AM
#32
2nd Gear Member
Thread Starter
Join Date: Oct 2011
Location: AL
Posts: 446
I wouldn't trust ANY method of removing head deck material that did not involve a large, heavy, and rigid piece of machine shop equipment. You're all but guaranteed to end up outside any reasonable flatness spec, which in turn will all but guarantee having head gasket trouble later.
I've hand-tapped a few things, but nothing as angularity-critical as rocker stud holes. It's way too hard to keep the tap straight and once it's started to cut crooked you've lost that battle (and may even break the tap off leaving a piece that's too hard to drill out stuck there in the hole). Don't do it.
Fitting the biggest possible valves can end up costing you power due to shrouding on the chamber wall side. A streetable 289/302 simply does not need 2.02's.
Building up your engine should be about putting together a good combination of parts. Not about individual spec numbers themselves.
Norm
I've hand-tapped a few things, but nothing as angularity-critical as rocker stud holes. It's way too hard to keep the tap straight and once it's started to cut crooked you've lost that battle (and may even break the tap off leaving a piece that's too hard to drill out stuck there in the hole). Don't do it.
Fitting the biggest possible valves can end up costing you power due to shrouding on the chamber wall side. A streetable 289/302 simply does not need 2.02's.
Building up your engine should be about putting together a good combination of parts. Not about individual spec numbers themselves.
Norm
As far as tapping the holes for the studs it seems like it would be really easy to rig up a guide for the tap. I'll have to check and make sure it's a true 90* angle on the current studs first. If all else fails I have a pretty decent adjustable speed drill press that rotates slow enough to where I could probably tap it with that.
01-08-2012, 11:02 AM
#33
6th Gear Member
Join Date: Feb 2007
Location: state of confusion
Posts: 7,635
That glass table had better be sitting on a thickish steel plate that is also flat, otherwise under the weight of the head the glass will deflect and you'll end up cutting more off the ends of the head than from the middle. It only takes a few thou for head gasket sealing to become problematic even with composition gaskets. Never mind if metal head gaskets might be used. If anything, the 4 bolts/cylinder SBF fastening arrangement is going to be a little more sensitive to this than the SBC's 5 bolts/cylinder.
Many years ago I saw a power tap machine used once, by an old-time machinist. Using a drill press sounds like a pretty shaky approach, because you still have to periodically stop and reverse the rotation to break the chips.
It's easy enough to visualize using something sort of like a lathe center to keep the butt end of the tap in position. But it might not be so easy to actually locate the axis of the center along the axis of the rocker stud hole. If you're off either laterally or angularly you still won't end up with the threads being cut straight.
The rocker studs are not perpendicular to the head face. The procedure given in the FRPP catalog for "head modification for mechanical cam" implies this by telling you to machine the tops of the stud bosses at right angles to the holes (as opposed to cutting parallel to the deck). They don't provide the angle because it is a general note, and the angle probably varies among the different engine families anyway.
Norm
Many years ago I saw a power tap machine used once, by an old-time machinist. Using a drill press sounds like a pretty shaky approach, because you still have to periodically stop and reverse the rotation to break the chips.
It's easy enough to visualize using something sort of like a lathe center to keep the butt end of the tap in position. But it might not be so easy to actually locate the axis of the center along the axis of the rocker stud hole. If you're off either laterally or angularly you still won't end up with the threads being cut straight.
The rocker studs are not perpendicular to the head face. The procedure given in the FRPP catalog for "head modification for mechanical cam" implies this by telling you to machine the tops of the stud bosses at right angles to the holes (as opposed to cutting parallel to the deck). They don't provide the angle because it is a general note, and the angle probably varies among the different engine families anyway.
Norm
01-08-2012, 02:26 PM
#34
2nd Gear Member
Thread Starter
Join Date: Oct 2011
Location: AL
Posts: 446
That glass table had better be sitting on a thickish steel plate that is also flat, otherwise under the weight of the head the glass will deflect and you'll end up cutting more off the ends of the head than from the middle. It only takes a few thou for head gasket sealing to become problematic even with composition gaskets. Never mind if metal head gaskets might be used. If anything, the 4 bolts/cylinder SBF fastening arrangement is going to be a little more sensitive to this than the SBC's 5 bolts/cylinder.
Many years ago I saw a power tap machine used once, by an old-time machinist. Using a drill press sounds like a pretty shaky approach, because you still have to periodically stop and reverse the rotation to break the chips.
It's easy enough to visualize using something sort of like a lathe center to keep the butt end of the tap in position. But it might not be so easy to actually locate the axis of the center along the axis of the rocker stud hole. If you're off either laterally or angularly you still won't end up with the threads being cut straight.
The rocker studs are not perpendicular to the head face. The procedure given in the FRPP catalog for "head modification for mechanical cam" implies this by telling you to machine the tops of the stud bosses at right angles to the holes (as opposed to cutting parallel to the deck). They don't provide the angle because it is a general note, and the angle probably varies among the different engine families anyway.
Norm
Many years ago I saw a power tap machine used once, by an old-time machinist. Using a drill press sounds like a pretty shaky approach, because you still have to periodically stop and reverse the rotation to break the chips.
It's easy enough to visualize using something sort of like a lathe center to keep the butt end of the tap in position. But it might not be so easy to actually locate the axis of the center along the axis of the rocker stud hole. If you're off either laterally or angularly you still won't end up with the threads being cut straight.
The rocker studs are not perpendicular to the head face. The procedure given in the FRPP catalog for "head modification for mechanical cam" implies this by telling you to machine the tops of the stud bosses at right angles to the holes (as opposed to cutting parallel to the deck). They don't provide the angle because it is a general note, and the angle probably varies among the different engine families anyway.
Norm
If I go the guide route then I'll probably secure it off of the other studs so that the angle is right. As far as making it centered, i'll probably secure a magnetic laser to the guide and aim it to the center of the hole. That's the best way I can think to do it anyway...
I've never used the drill press for tapping, but I have used it for extracting broken bolts. I probably won't end up using it though simply because I don't feel comfortable tapping something that I can't feel.
remember though I got these heads cheap to try this stuff out on. I'm fully prepared to turn these things into a small coffee table or something if I screw them up.
01-08-2012, 06:43 PM
#35
5th Gear Member
Join Date: Nov 2006
Location:
Posts: 2,106
The 1/2" glass surface may get you past 1/10th" mark, its gonna flex. Fully tempered, maybe into the 100th range. Nothing is going to beat the right combo of parts and a good reputable maching shop to prepare them.
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