Corksil

Hey this is a simple question but I can't find the damn answer anywhere.

I have a gauge probe I want to tap into my cylinder block.

The gauge probe is labeled as [1/8" PT] - it does NOT appear to be tapered

Should I use an 1/8" NPT tap?

I need this to seal up well enough to hold 120psi fluid @ 300*F

Thanks.

Sprockets

iTrader: (6)

If I remember correctly from years ago...male BSPT can go into female NPT, but not the other way around. If the threads aren't tapered, it won't seal. Are you sure it's not tapered? What brand is the gauge probe? Japanese usually use BSPT, but they're labeled PT.

Corksil

Innovate gauge, MTX-D and feliepes customer service fellow told me that "PT and NPT are both interchangeable" (which I highly doubt is completely true)

The manual specifies the probe as 1/8" PT and does not say anything else.

Hard to tell but I believe this is tapered...


And this does not look tapered at first glance, but it appears that the threads actually get wider halfways up the thread, then taper back down... as if they balloon wider in the middle.

Corksil

BRB buying dial caliper gauge thing.

nub

PT = pipe thread which there are more than one type.

Your second pic looks tapered to me. Maybe not as noticable as the first pic because it doesn't have the parallel surface of the probe on it.

Corksil

Okay well lets assume that all the probes and sensors are NPT with the usual 3/4" per foot of pitch. (1/16th" per inch in other terms)

So a simple 11/32" hole drilled, then an 1/8" NPT tap, some teflon - and everything should tighten up and seal 120psi of 300*F fluid?

or am I missing something.

Sprockets

iTrader: (6)

First picture...NPT on left, BSPT/Japanese PT on the right (came with an Omori EGT gauge). The second picture is the label for the NPT adapter in the first pic on the left.

Corksil

Uh... thanks I suppose. Not sure exactly how your defi gauge has anything to do with what I'm talking about but hey, pics are fun to look at!

Sprockets

iTrader: (6)

I appreciate the sarcastic comment. I'm showing you the difference between BSPT and NPT (side by side), which is what you're trying to figure out, correct? I took a picture of the Defi package (not for the gauge, but for the adapter), to show you that Japanese gauge manufacturers write "PT" on there when referring to BSPT.

Your first picture is tapered, the second is not.

Corksil

Thanks for your help.

Yes I agree - upon visual inspection it appears that my first picture is tapered and the second is not, just like you think.

Do you think that BSPT is interchangeable with NPT?

I've got a female 1/8" NPT fitting arriving in the mail, which I plan on threading the silver male (1/8" BSPT) probe into..

Thanks.

Sprockets

iTrader: (6)

I currently have my OEM BSPT oil pressure sensor and BSPT oil pressure sending unit screwed into an NPT T, so that's fine.

Khnemu

iTrader: (1)

They're interchangeable but what I've read is you need to run a tap through the threads for it to work correctly. BSPT threads need a NPT tap ran through to correctly use a NPT gauge or sensor.

wantboost

iTrader: (2)

Bspt and npt are completely identical except for the thread profile.. npt has straight, sharp edged threads where bspt has rounded threads.

They will interchange just fine, especially since you're supposed to use Teflon on the joint.

Khnemu

iTrader: (1)

Could you substitute Hondabond for teflon paste or tape?

wantboost

iTrader: (2)

No, Honda bond is only to be used on mating surfaces.

Khnemu

iTrader: (1)

Thanks wantboost. :O

Sprockets

iTrader: (6)

The TPI is different between them. For example, 1/8" BSPT is 28 TPI and NPT is 27 TPI. The thread angle for BSPT is 55º, NPT is 60º.

Corksil

So it sounds like BSPT is commonly called simply "PT"

I ordered a few parts for the pressure sensor sending unit and I think I have that figured out. I'll tap the sandwich plate for the vtack conversion for 1/8" NPT and thread one end of the braided line into it. The sending unit will connect to the braided line with a 1/8" NPT coupler. It looks like the threads on the sending unit ARE tapered in this picture... But it threads in 3 or 4 rotations before it binds up and starts to feel tight. I think teflon and a gentle torquing will cause the two to mate up perfectly without leaking.

Dial caliper is in the mail arriving tomorrow/monday SO I'll be able to verify if the sending unit has tapered threads or not

Corksil

Gonna go have a day in the shop hopefully will be getting the intake manifold off so I can test fit the oil temp sensor (1/8" PT also) in the back of the block where the OEM sensor is.

Will update w/question

Sprockets

iTrader: (6)

In that picture you can definitely see the taper. The first picture you posted makes it look like a regular bolt. Teflon paste will help.