tapered or parallel thread for EGT sensor

[PhilipA]

I am soon to have a TD5 manifold ceramic coated and plan to drill it for an EGT gauge at the round casting mark just before the turbo.

1 Should the hole/thread in the manifold be 1/8 NPT tapered or parallel?

2 I assume that a steel plug will be needed rather than aluminium as I plan to get the EGT gauge in due course rather than straight away

3 any other suggestions for siting of the sensor?

4 any experience on whether the heat shield can still be fitted with the sensor in that position, as planning for a 90degree bend sensor.
Regards Philip A

[justinc]

1/8npt is the go. The probe can fit with the heat shield. We drill them close to the flange slightly toward the front so the 90? probe comes out under the shield with room to spare. Use a 1/8 npt brass blanking plug.

Jc

[kelvo]

I modified my heat shield to allow it to fit the the 90* probe I had. This is using a 1/8"NPT into the manifold casting mark

[northiam]

Taper... everyday

https://en.wikipedia.org/wiki/National_pipe_thread

[Roverlord off road spares]

I modified my heat shield to allow it to fit the the 90* probe I had. This is using a 1/8"NPT into the manifold casting mark

Neat job

[PhilipA]

Taper... everyday

It was explained to me today by an ex Royal Navy engineer who now builds steam engines, that the taper is on the male thread and not on the female.

This seems to be supported by the fact that they sell 1/8 NPT taps as tapered (starter) taps and parallel finishing taps in sets of two although they do sell them separately.
Anyone disagree with this info?
Looking at the Wikipedia entry seems to support this.
Regards Philip A

[bee utey]

It was explained to me today by an ex Royal Navy engineer who now builds steam engines, that the taper is on the male thread and not on the female.

This seems to be supported by the fact that they sell 1/8 NPT taps as tapered (starter) taps and parallel finishing taps in sets of two although they do sell them separately.
Anyone disagree with this info?
Looking at the Wikipedia entry seems to support this.
Regards Philip A

Both of the two taps in my 1/8" NPT tap set are tapered thread, not parallel. One of the two has a bigger lead in ground onto it. I would never use a parallel thread tap as you couldn't control the depth engagement of the male fitting. The hex section of the fitting should not bottom on the face of the item you have tapped a thread into.

[northiam]

I purchased a similar set recently in 1/4 NPT both taps sure look tapered
Regards
National Pipe Thread NPT TAP SET Boxed Starter Plug 2pc SET From 1 8" 1 1 2" | eBay

[Don 130]

I recently fitted an thermocouple to my 300TDI. After much asking of questions I'm convinced that both the male and female threads are tapered.
Don.

[PhilipA]

And the correct answer IS..............
TAPERED.
I bought a 1/8 NPT tap and brass plug from the great little shop that is Gosford Bolts and Bearings.

Funnily enough the tap had scribed on it DRILL 9.3MM. Anyone know what that means as 8.5 MM is the correct drill size and AFAIK there is no such thing as a 9.3MM drill.

Ironically they cost about $22 for both which is cheaper than ebay.

I had to drill a 8.5 MM hole and I drilled about 0.5 MM with a 9MM drill to start the tap.
I have not tapped to the full depth of the tap leaving about 1-2MM at the top so that the plug would not bottom out finger tight. I can always tap a bit more if the EGT sensor is a bit too tight.
The position is in the casting mark on top of the manifold near the turbo flange as in the posting above by Kelvo.
Thanks Kelvo that was very helpful.
Regards Philip A
So much for old RN engineers.