I am getting finished with installing my guages and I am having problems in getting the hole tapped. What is the proper way to tap?

I drilled it out the hole with a 21/64 and I am using a 1/8 NPT to tap. I tap about 3 threads in. However, I can't even hand thread the thermocouple. the threads on both look good.

I am installing on ramped maniforld like here:

http://www.dieselmanor.com/diy/CMS3-gauge/G3image3.htm

Any ideas?

 

I believe you have to run the tap in further than that. Are you working the tap back and forth to remove chips?

You should run the tap in 1/2 to 3/4 of its length. Do not go past 3/4 of the taps length or your hole will be too big to get a tight seal on the fitting.

 

Ok thanx. I am no where near that. Do I need to apply lots of pressure on the tap to thread? This part is remarkably slow and I am taking my time. Two hours into it... The hole is opened to 21/64, the drill bit slides through like butter.. There is much resistance on the tap, so I think I have broken anything yet.

Again thanx!

 

Yes, there will be a fair bit of resistance - remember you are cutting threads into the cast iron manifold. Make sure you get the tap straight, and also remember to reverse the tap every 1/4 turn to break the chips off.

 

If you are installing the probe pre-turbo, did you take any precautions to prevent large metal chips from falling into the turbo?
The evil doc is correct, but don't open the threaded part too large or you will end up with too much sticking into the exhaust flow.

 

Yeah. I loosen the turbo and slid some cardboard between that the manifold. Again thanx. I will finish it at first light.

 

You dont really have to do that.

When i drilled mine I had a buddy stand there with a shop vac. I used some grease on the tap when I tapped it (yes, I know you are supposed to tap cast iron dry). And then ran a q-tip (with grease on it) through the hole to pick up any chips that may have dropped.

 

Cutting oil is your friend.

http://www.ridgid.com/Tools/Thread-Cutting-Oil

 

Thanks, got it done. Less beer made the difference.

 

Cutting oil is not recommended for cast iron or non-ferrous metals.
I don't see what all the chip paranoia is about, they all blow out the exhaust before the engine finishes it's first ten revolutions.

I've installed dozens of pyros and don't do anything at all about the chips,
never a problem.

 

Really?

http://www.grainger.com/Grainger/items/2RPA9

Have you ever tried threading black iron pipe without thread cutting oil?

 

Black Iron pipe is a ferrous metal that is why you need cutting oil

 

No, never tried without oil, but it's not cast iron.
It's the same as galvanized pipe without the coating.

 

So what is recommended?

Nothing?

 

me too...............