This tutorial is for the tool geeks like me. If I can get the original tool for a job for an affordable price I'll get it. If not, well, time to think and make it.
The tool we'll make here is a copy of the Puch Dial Indicator, Puch Part# 278.
Total costs to build this will be in around 20$, but you will have parts to spare.
Pictures found in forum source
1 Dial Indicator, Harbor Freight, with coupon 12-14$ (1 In. Travel Machinist's Dial Indicator, Item#623)
1 Spark plug, this one was 2.38$ at Advance Auto (Its an NGK BKR5E I had left over from a car)
1 O-Ring Assortment, Harbor Freight, 5$, pick what you like
1. Shades...yes, nothing like porcelain in your eyes, put on your shades and look smooth while staying safe
2. Dremel with a cutting disc and sanding sleeve (or other cutting tool, hacksaw works but put in some sweat)
4. Vise (makes it easier, but you can do without)
5. Hammer (big or small, doesn't matter)
6. Something to knock out the ceramic, like a 1/4 wrench extension, an old bolt, ...
Put on your shades, pull out your plug, and put it in the vise (or hold it if you dare). Make sure, if you put it in your vise, you don't damage the threads. I leave the carton around it for that purpose.
Now, using your dremel with a cutting disc, cut around the sparkplug where the porcelain ends, there is a little lip that holds it in. It's thin metal, it wont take long. Cut around the whole plug.
Now cut off the ground electrode. That was easy, wasn't it?
Hammer Time!! Clamp the plug upside down into your vise. Center your extension/bolt/nail/whatever on the electrode and give it a couple gentle tabs. It wont take much, the whole porcelain and electrode will come out in one piece. If you hulk out here you will learn why you are wearing glasses. Be gentle.
Back on the dremel, use the sanding sleeve to smooth out any jagged edges you might have on the plug. We want nothing pitting the cylinder.
Now we drill a small hole at the end of the threaded portion (up, where it doesn't make contact with your cylinder) to avoid having compression interfere with our funky fresh tool. Make sure there are no shavings/jagged edges after you drill.
Take your dial indicator, fit it with three snug o-rings and insert it into the plug base. There will be enough friction to hold your dial in place and to gently screw the assembly into your cylinder.