Trying to fit a 60's AMC intake manifold on 70's heads. The center two holes on each side need slotting/milling to line up. AMC in their wisdom decided to relocate these holes so techs wouldn't mount late model 401 intakes (breathe better) on 390 heads/blocks. When drilling the holes, the holes become siamese'd and the drill will walk over to the original hole while drilling. The manifold is a 1/2" thick. I've read, use a ball end mill and a drill press or mill but the articles don't say how to. I don't have access to a mill. There is an X and Y axis the drill bit must be perpendicular to. And the object should be clamped to the drill press table. Takes a level to get things right. It is near impossible to clamp an intake manifold in a position for drilling. Has anyone had to perform this feat? If so, please advise. Here is one done on ebay. See pic.
If you want to drill a precision hole you can create a "drill jig" using an appropriately sized steel plate and some "drill guides". You can get drill guides from the better industrial supply houses.
Don't know where in the Bay Area you are. But I know a guy in San Mateo who has a Bridgeport and nothing better to do. If you want to reply with a PM.
Without access to a milling machine I think your best approach would be as R Pope has suggested. Scribe out the lines you need to make the slot , hog out with a die grinder and finish with a file to the right size/shape. "Drill guides", or what I know as drill bushings, will require a drilled and reamed hole of precision size to press into. They can also be slip fit but will still need a precision sized hole to fit into. Also standard end mill will do the job better than a ball type if you are able to gain access to a mill.
A mill with a big table and a system of clamps would be ideal, but only if you know the exact degrees and distance to splay the 4 new hole centers, etc. Otherwise you're just guesstimating and will be somewhat sloppy to within a couple thousandths anyway. In your situation, I would just use a Dremel or hand drill with one of those bits designed to cut sideways. Use a black marker and a good gasket as a template. Then cut away maybe checking the fit once or twice.
So it's only 4 holes right? And they overlap the original holes. Buy a round coarse file smaller then the diameter of the hole and a fine file just a little smaller then the hole. Use a new gasket with the correct hole spacing and scribe the bottom of the manifold to the new pattern. Then take the coarse file and have at it, after all it's just aluminum. Then when you get close to the scribe ones switch to the fine file and finish it. Have a wire brush handy to clean out the files of aluminum chips if they get clogged. That's the old school way to do it, shouldn't take more then 2 beers worth of time to do all 4 holes.
Thanks guys. This has been the go-to forum when it comes to being mechanically creative and thinking outside the box. Thanks for all the input. Now, gotta go up to Home Depot for more tools.
Since you are only doing one, how about making a jig from a block of hardwood with one or more holes drilled at the appropriate angle, that bolts or clamps to the manifold?
Which ever way you decide, acquire some “ Rapid-Tap Aluminum “ it will make the job easier. In the Firetruck business we use a lot of aluminum, this stuff is a life saver working aluminum. Bones
Junkman uses a method similar to mine when a drill press is handier than firing up the mill. I sometimes take a 1/2 or 3/4 thick piece of metal, drill the hole I want in the thick plate, then tightly clamp it in place (in this case, against your intake gasket surface) exactly where you want your finished hole, then simply run the drill bit thru the hole in the plate again. This forces the drill bit to stay perfectly in place where you want it without having to use hardened drill bushings, or milling machine, or having to grind or freehand anything. Just clamp the THICK plate with the hole exactly where you want a new hole, and let the thick plate force the drill bit to stay in the right place. feed it gently if the drill bit is chiping away at only one side of the manifold hole. WHY BE ORDINARY ?
WOW! Thanks for all the great ideas. The collective brainstorming on this forum reminds me of how "TEAM SCORPION" works together in the TV series. I will try two of the procedures mentioned out of curiosity and decide which procedure works best. Then, make the remaining two holes.
since its a one time thing I would just put the intake manifold gaskets in place, mark the bolt locations on the manifold, center punch and drill. but that's just me
Last time I needed to do something similar [Speedway valve cover adapter with hole drilled 1/8th inch off] I filled the 1/4" hole with a piece of 1/4" aluminum dowling as per Sunbeam's suggestion. Used red loctite to keep it in place and redrilled the hole in the correct place...couldn't tell I made any modifications.
Another good way to fill a hole in aluminum. Drill hole, chamfer the ends slightly, press in aluminum rod that is slightly too long, peen the ends and file flat.
I'd have been all over Rich Fox's suggestion. 5 minutes in his mill and an hour or two of me asking questions about what he's done.
Wanted you all to know I appreciate the suggestions. The advice didn't go in one ear and out the other...put them to good use. Used an aluminum rod to plug old hole, used intake manifold gasket to trace where new holes go, used champagne bottle cork wedged against Air Gap intake manifold and aluminum rod to keep the rod from pressing out, drilled pilot holes on drill press table and drilled up to 7/16" holes, the holes overlapped/siamese'd, removed aluminum rod. Drank the champagne. Cheers
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