I received a PM earlier this week from a fellow board member here, "Pick". He read my build thread and had some suggestions and motivation for me to repair coolant temp sensor hole in my cylinder head. My biggest take away was his suggestion of using a tapping block when I tap my threads. I have heard about these but I have never used one. It sounded exactly like what I needed and would certainly help with my biggest concern. I researched what was available to buy, but I couldn't find anything that was near the size I needed (0.555"). So, I decided to make my own. I had some scrap round stock that was perfect. The lathe made quick work of it and I had exactly what I needed. This should work great, thanks Pick!!!
The tap I am using for this job came with the 12x1.5 HeliCoil kit I bought. It also came with the drill bit, installation tool and 5 new steel threads.
First thing I did was rotated the block until the plane I was working on was upside down but parallel to the floor. I needed to make sure that any metal shavings that are created have a chance to fall out of the head. Next, I put some grease on the supplied drill bit and started drilling out the hole. The grease should catch all of the metal shavings. I went very slow and only took out two old threads at a time. Each time I stopped, I cleaned the shavings out of the drill bit and replaced the grease. I also kept vacuuming the hole out. Here is the hole after all passes were complete.
Next, I put cutting oil on the threads of the supplied tap. I used the tapping block to make sure the new threads were tapped perfectly straight. I cut about two threads at a time and back out the tap. Again, making sure I clean up the shavings from the tap and vacuuming out the hole. I continued oiling the tap and cutting threads until it was complete.
Next, I used red Loctite and inserted the new threaded coil into the hole with the supplied tool. I was a bit tricky to get it started but once it did, it only took a little pressure to keep it threading to the end. I used a pair of needle nose pliers to pull the installation tang off of the coil. Here is the finished product after waiting 24hrs for the Loctite to dry.
The last thing to do was finish it off with a nice plug. I found a nice stainless plug with copper crush washer at McMaster-Carr. I used high-temp thread sealer and torqued to 15 lb/ft. This thing is sitting 100% flush! What was I ever worried about???
