Snug spark plug boots

[BigTallDad]

Quite by accident I discovered that vinyl insulation on electrical wire has a “memory”; if stretched, it will revert to its original size after the stretching implement is removed. Here are the components of a plug, the boot, and the plug wire. I used .030” styrene rod for the plug, and eyeballed the size for the boot and the wire. Note that the boot is slightly larger than the wire and the plug, but the inside diameter is still too small to insert the styrene and wire.

I used a common push pin as a stretching tool. Place the boot on the point of a push-pin, stick the pin into an eraser or similar material (corrugated cardboard works very well too), then work the boot to the thickest part of the pin. Although I'm only showing one boot, several can be placed on a single push-pin. I discovered (the hard way) that you need to let the pin do the stretching for at least an hour; the longer the vinyl stretches, the longer it takes (within reason) to return to the original size. If you only wait a few minutes, the vinyl shrinks almost immediately and you’re back to square one.

I set the stretched version on the sample to give you an idea of what the stretching will do.

Note that the boot is larger in diameter (and can be worked with easily) but is a bit shorter. Don’t worry, when the almost-original diameter returns, the length will too.

Place the styrene in some kind of clamp (I use a vacuum-base vise). Working rather quickly, remove the boot and slide it over the styrene; place a drop of CA on the end of the styrene, slide the boot over the tip of the styrene (leaving room for the plug wire), and insert the plug wire into the boot. After the boot has returned to the original (albeit slightly larger) size, trim the styrene rod to the desired length.

Use a number 68 drill to drill the holes for the plugs and cement the plugs in the holes, leaving a portion of the white (to represent the porcelain on the spark plug) exposed. After all is said and done...

[Skip]

Good observation and trick, I've used a sewing needle to do the same.

[bobss396]

I have drilled spark plug wire holes extra big, so the boot material slides right into the hole. This depends on how much material you have to work with. I'd be hesitant to try it on 3D parts since they are brittle compared to kit plastics.

I have a bunch of wire that measures around .037", I use that for boot material. I slice through the jacket, leave the core wires un-cut and slide the "boots" off the wire.

I leave the boots long, most of the time they compress enough and don't need glue. The height can be set very uniform, the wire-wrap wires that go into the boots you can get away with not gluing.