CHT nightmare

[chateau]

Decided to replace the CHT sensor in my 84 3.2 as I am replacing the reference and speed sensors. Thought about it for a few days " What about if I cut the wires and then cannot get the CHT sensor out?". Well that is just about what happened!! Should have trusted my instincts!! Cut the wire and then tried to back out the sensor, well after 26years you can imagine it was not going to be a ' piece of cake". Eventually it started to move but after a few turns it got stiffer, so WD-40'd it tightened it back in a bit and then backed it out, after it was out 5mm, it just kept spinning and would not go in or out!!. A few choice words like 'golly gosh!!' and ;'Oh bother' were heard. I managed to get a broad screwdriver around the back and into the gap between the Head and the CHT and as I started backing out the CHT a bit more I turned the screwdriver in the gap to help force the CHT out. It worked, although the threads on the CHT are stripped I think the threads in the head are OK but just need to be tapped to clean them out. It could have been worse!! Does anyone know what the thread specs are on this hole for the die size. Thanks all.

[GH85Carrera]

I can't help you on the thread size. I can warn you there might be another GOLLY or two in your future. Getting the rubber grommet back in place is a pain. Use some lube on the grommet and it will help go back in. Good Luck!

[chateau]

FYI the thread spec is 1/8 NPT 27. Getting at the hole to tap the threads was a PITA. I had to reverse a 2" - 1/4" extension bar from a socket set then add a U/J and then another 4" - 1/4" extension bar and then the T-bar. Fortunately this worked and managed to clean the threads. I also ran a die down the thread on the sensor to make sure everything matched. The sensor went in well for about 4 threads and then started to tighten up so I backed out the sensor and re-tapped the hole to make sure it was clear and then blew the hole out with WD-40 to make sure there was no swarf left. The sensor still tightened up after about 4 threads, wound it in until there was about 1 thread left and stopped as I did not want to end up with a totally screwed sensor that was going nowhere. Have run the car and all seems well. By the way the grommet was the easy part!! Just wiped some grease around it and it slipped in.

[rick-l]

Where did you get a 1/8 inch NPT (National Pipe Tapered) tap? How far did you run it in?

[chateau]

The 1/8 NPT 27 came in a metric set. The hole is depth is pre set so I just ran it as far as it would go. I measured about 7/8 threads. As the thread is tapered I suppose that is why the sensor tightened up the further it went in. Found this for you. http://hand-tools.hardwarestore.com/22-409-taps-pipe/irwin-pipe-tap-298869.aspx

[john walker's workshop]

just so you know, the threads are 10X1.0 mm. they are not tapered.

[chateau]

I stand corrected. Wish someone had told me before when I first asked. I have a metric set and the 1/8 npt was the only die in the set that fitted on the sensor, the others were too coarse. Still it is in the car and the car is running.