Heli-Coil a stripped carb inlet

Mon Feb 12, 2007 4:47 pm

Hello everyone. Here's the hot set-up that Phil (PWL) used to heli-coil two(2) bad I.H. carb inlets that were stripped out. All this was performed at George Willer's High Tech Machine Shop :wink: .

There have been other's do this project, but Phil has it down to a science.

Phil made a jig out of a piece of flat stock about a 3/8" thick by about 4" wide and roughly 8" tall(can be made shorter if room is a problem). He machined the plate so the carb would bolt close to the top corner, and still allow room for the throttle linkage plate to clear the side of the jig. Phil bolted the carb to the jig with two 1/4-20 allen head bolts. Here's the first pic of his jig with the carb mounted.

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The next step was to clamp the jig in the mill vise, making sure you align the jig square, and setting flat in the vise, so the drilling is done straight into the hole.
The next step was to install his dial indicator into the mill. Phil lowered the indicator into the area between the seat and the screen, and centered the carb body. He used a 1/2" end mill(4 flute) to do the drilling, which will leave a flat, bottomed out cut. Phil also adjusted the stops so it would only cut to a max depth of .340, stopping short of the tapered seat that the ferrule will compress into.

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Next was to install a center into the mill. Pics soon to come. Phil then installed his first heli-coil tap into a tap handle, placed it into the carb hole, and lowered the center onto the tap, allowing for perfectly straight threading into the carb body. Then he installed his second heli-coil tap, hand ground into a bottoming tap, so the threads would be as deep as possible.

He then blew everything clean with an air hose. Make sure you remove the small screen before you blow things out, or you could send it flying across the room :shock:

Next was the heli-coil installation. This is Phil's kit of his two taps, end mill, and the installation tool.

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Phil screwed the heli-coil into the hole until it was roughly one thread away from bottoming out. Pics to come soon. He then installed a drop of lock-tite down into the heli-coil. Then he snipped off the heli-coil flush with the carb body, and then finished screwing the heli-coil into the hole till it bottomed out. This left the outer end of the coil just below the surface, for a nice neat looking job. There is roughly 4 heli-coil threads installed in this repaired hole.

I'll get the remainder of the pics on this post to explain the missing details, in case it's too confusing for some.

Hope this helps.
Rick