Retapping BSPT to NPT

[unclemat]

I have a "sandwich" adapter, that goes between the block and the oil filter. The purpose is to hook up oil temperature/pressure sensors.

The holes have 1/8 BSPT threads, and I have sensors with 1/8 NPT threads. I am thinking about retapping the holes to NPT, rather than using adapters.

Would it work? Any suggestions how to do it right would be appreciated. Btw, the piece is aluminum.

 

[nissan_crawler]

I have a "sandwich" adapter, that goes between the block and the oil filter. The purpose is to hook up oil temperature/pressure sensors.

The holes have 1/8 BSPT threads, and I have sensors with 1/8 NPT threads. I am thinking about retapping the holes to NPT, rather than using adapters.

Would it work? Any suggestions how to do it right would be appreciated. Btw, the piece is aluminum.

Retapping is bad, bad, bad. You can't cut threads through existing threads.

HOWEVER, depending on the size of pipe thread it is, it's either the same thread count, or on more than npt. Honestly, for my oil sending units on my nissan, I have 1/8" brass npt into the 1/8" bspt in the block. They have different degree thread, but it works fine, hasn't leaked in ten years. Most people I know do it this way.

The only other choice is adapters.

 

[PoorOwner]

I think the NPT has 1 less or more thread per inch than the BSP in 1/8"
So tapping with NPT can be bad but it had been done before.

Personally I have also just installed NPT fittings into BSP (assuming because it was a Japanese car..) it's non tapered, and it works fine. I recommend permatex form a gasket 2 as sealant just in case, if it's a oil joint this stuff works great.

You can use adapter too as long as it is not too long and create a weak point.. (I installed a tee before to use 2 senders and it snapped right off after a while on the freeway.

 

[unclemat]

The adapters ****, especially for oil temperature sensor - it will be less accurate because it won't protrude into the oil path.

I tried (lightly) to screw an npt sensor into bspt hole and it binds quite soon. I guess I could force it, but I am afraid about buggering the threads on the not so cheap sensors...

Perhaps I should drill new hole and tap it with NPT. The oil sensor I plan on mounting remotely with braided hose due to clearance reasons, so I can get bspt adapter for it.

 

[scofo]

Hello UM, If there is enough room in the boss of the "sandwich" maybe you could go up to 1/4" NPT and use a pipe bushing. You may be able to "work it over" with your 1/8"NPT tap so that you oil temp sensor protrudes into the oil flow. Good luck.

 

[PoorOwner]

for oil pressure sensors I always relocate with braided AN3 or AN4 hose, less chance of snapped, an expensive gauge usually come with a hose.

Isolated from vibration for longer sensor life, don't have to worry about the thing snapping off, hitting a rock etc.. losing all your oil and possible engine damage.

 

[unclemat]

Thanks guys for suggestions. I decided to buy another sandwich adapter with npt holes. Will be plug and play.

It was kinda necessity anyway since as it turns out, I needed the bspt threaded sandwich on another car with Defi sensors, which are bspt threaded. A *@^$@*^$%! dealer's monkey who worked on the car, overtorqued the bolt holding the sandwich adapter already present on that car (I had to use breaker bar to remove it!). It made it crack inside. Nothing was leaking, but it was cracked half way thru. If it cracked all the way thru, the adapter would have fallen off with filter, cut off the oil and likely killed the engine.

I truly hate letting others work on my cars, but it was warranty repair (engine short block replacement).

Good thing about the npt/bspt mismatch. While changing oil I decided to check the adapter already mounted on the car, being curious if it's bspt or npt.

 

[russlaferrera]

One more suggestion. If you have the room. You could drill and tap a 1/4 NPT, use a bushing to 1/8 NPT.

 

[ntsqd]

I know that the issue is solved, but:
1/8" BSP: 28 TPI
1/8" NPT: 27 TPI

In a typical thread depth of under 1/2" we're talking less than 1/2 of a thread difference in pitch. That wouldn't bother me at all to re-thread.

What would make me look twice is the difference in major thread diameters. No idea how much those differ.