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I rebuilt my carburetor for my truck, and wanted to replace the choke thermostatic coil. The coil's hold-down bolt twisted off at the manifold. Before I drill and tap/heli-coil it, I want to know if it is a blind hole....and maybe someone knows how deep? I suspect so, but the last thing I want to do is introduce metal shavings to the innards of the engine. 402 BBC.

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I would heat it first then try a left hand drill bit might come out without going the whole heli-coil route

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Yeah, I'm going to have to buy some left hand twist drills. It's in a puddle of Deep Creep at the moment.

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If you have access to a welder I’d try and weld a nut to it and spin it out before drilling. It normally works pretty good.

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Blind hole iirc good luck!

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On my 350 manifold, the thermostatic coil screw hole is a blind hole and is 1/2-inch deep. The screw that goes in the hole is only about 1/4-inch long. I can take a photo if that would help.

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It sheared off at the manifold, nothing is sticking out.. I'm waiting for my son to come home for lunch. He has left-hand drill bits. I went to Harbor Freight but they only carry them online.

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I was thinking that it should be blind, but I don't want to guess.

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I wanted to remove the coil and housing on my 307 but the screw wouldn’t budge. Leave sleeping dogs lie.

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If I was the only one to drive this truck, I could run a manual choke in a pinch. But everyone else around here has to have it turn key like a new vehicle, or they can't deal with it.

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The screw is a machine screw.. IIRC, the size is 6-32.. Drill it out and tap it to the next size (8-32??) and be done with it..

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Yup, that is what I just finished doing! I had to put the tap in my drill, though, because I didn't want to completely remove the carburetor. I should have looked closer before installing the carb, and addressing the choke coil first. I flat-rated it out of the way with the hoses and linkage still attached (except the fuel supply) and diapered it off to avoid metal chips down the intake. That coil is different from the one that was on there, so I had to make a new choke link. Welding rod ftw! :lol: My arthritic knees finally made the end of the day. I'll finish up tomorrow. 🍺

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Not too late to just bolt on an electric choke and forget that mess ;-)