Clearancing heads for pushrods

[Bucky]

I have a project with a set of Brodix Track 1's of mine. I have had the pushrod area welded up for some extra meat to move the pinch over for the intake port. I have offset lifters and rockers are also T&D offset. I have a mill that I can set up for clearancing, but is there an easy, straight forward way to determine where the clearance should be? When you mock them up, of course the pushrod won't fit, so you are guessing a bit. Also, is the angle generally different than perpandicular to the head gasket surface? And finally, is there a long tool someone would suggest for plunging down that distance? I suppose the larger the diameter you use, the more leeway you have for error.
This isn't something I do every day, but I like tackling things like this. But any advice would sure be appreciated.

[andyf]

You might think about doing one cylinder by hand while the head is on a bare block. Then once you know what it needs to look like, set it up on a knee mill with a rollover fixture and duplicate the first cylinder.

[Bucky]

That may just be what I do. Thanks!

[bill jones]

-I took a really coarse round rasp style file----rounded off the nose to where I could spin it in a dedicated lifter socket---modifed the rat tail end to fit into a 1/4" square socket---and spin that either direction with an electric drill.

-works pretty decent if you have an empty block sitting on an engine stand to bolt the heads to and you have the time to trial fit the rockers etc.
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-the tops of the paired intake pushrods are definitely tilted away from each other.
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-I can tell you this about milling the outside of the port walls--when you use an endmill that is long enough to cut that entire length outside the port---deflection becomes a BIG issue---to the point that holes or the curves drift quite a ways off center due to the torque of the cutter teeth to the surface.

-If I had to mill the pushrod holes I would personally use a left hand rotation end mill to do the one side and a right hand end mill to do the other side---so that the deflections sort of mirror each other.
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-here's a picture of a positioning jig I built to get the holes located pretty precise.

[Bucky]

I like that jig. My pushrods are nearly vertical since I am using offset lifters as well. So I can't use the center of a lifter bore as my reference. I can sure see what you mean about the deflection. Makes sense.

[Ken_Parkman]

I did a set (different head and engine) on Saturday. Using a head, rockers and lifters that let me mock up the pushrod (87 degrees from the deck in this case) I was able to figure out how far out to machine. I have a block block print, so with that I was able to calculate the indexing of the table on the mill. Then, used a long 7/16" endmill, and like Bill says there is a serious problem with deflection, I snuck up on it very carefully with small cuts to keep the deflection down. Very tedious and time consuming, but the result was nice.

[Bucky]

What overall length did you use with the 7/16" end mill?

[Bucky]

I didn't realize the cost of a longer one. I am going to have to do a better search through my tooling! Does this one look appropriate?

http://www1.mscdirect.com/cgi/NNSRIT2?P ... rchResults

[Ken_Parkman]

Similar, but much cheaper in HSS.

[Strange Magic]

You draft your two points right on the intake face as pictured, without the pushrods in place. Your complete rocker system needs to be in place and your lifters need to be in place as well. Use a straight edge and machinist ink on the intake face. I do this all the time in the shop.

[Strange Magic]

I also plug and move pushrod holes as well in the shop. Thats always an interesting project.