I'm just trying to run a thread up the outside of my STi air temp sensor and so I can then tap my intercooler for it. One slight problem I've never done it before and the sizes that I've got hold of are the exact wrong ones LOL

The OD of the bit of the sensor that I need to thread, which is plastic btw, is 12.5mm, so roughly half an inch. The biggest die I have is an M12 x 1.75 which will carve huge swathes of plastic off it, by the looks of it a couple of mm off all the way round.

Hmmm, I thought, seeing as it's roughly half an inch what about a 1/2 inch die of some kind, but of course it turns out that imperial thread sizes are totally on a different planet. Weirdly the closest that I can look up that might work is 1/4 inch BSP. Can anyone confirm that if I could get hold of a 1/4 BSP tap/die, that this would thread my 12.5mm plastic sensor nicely, and not too deep, i.e no deeper than say 0.5mm into the plastic, because otherwise it starts to actually turn it down like a lathe would!

The other thing is, I thought at first I'd want a fine thread pitch, because the metal of the intercooler is only a few mm thick so I want as much thread in there as possible. But then I thought that actually to allow the plastic to show a clear, strong thread, maybe I should go coarse instead?

Help!

 

have a look here : NAMRICK : TAPS & DIES

 

TAP 9/16 BSF
DRILL 12.7-0.5000-1/2
Might Help......................

 

Can I suggest you just use the inlet temp sensor to measure the temperature at the filter? You should certainly consider it if you're having problems with threading the STI sensor. Personally if you wanted to thread it into anything, I would get a metal threaded boss say m18x1.5 thread (lambda bung size), drill it out and araldite the plastic bodied sensor into the middle of it. I don't think you will reliable cut a thread onto the body of the sensor, and have it stay in one piece.

 

Cheers all! Yes Paul I might well go with that idea. I've got it in the cold air pipe at the moment, in the standard location, but I'm interested to see if it can accurately measure charge temp rather than incoming air temp, and see how it can cope with rapid temp changes. If so, it'll be handy to have it up on the FC Commander. Plus I want to see what difference it will make to the charge temp pattern when I fit a front mount, just before coming to you for another tweak of the map.

 

Agree with Paul, but if you need to cut a thread in thin walls use as fine as possible. M12 fine is 1.5, but i have M12 X 1.0 (which is a special) if you need it.

 

Ah, so the 'fineness' of the thread is also how deep it goes in as well?

Well I've been rummaging around in my plumbing drawer and have an old brass stop end with a 1/2" BSP male thread on it. There's just room to drill a 13mm hole through, stick the 12.5mm part of the sensor through and araldite it, job done. Then I'll just use a 1/2" BSP tap to fit it where I want it. Which is handy because I also need the same tap to fit a 1/2" BSP hose tail into my home-made catch tank!