What tapered thread system do Toyota use? (1 Viewer)

[Eurasiaoverland]

Wasn't sure where to post this question.

The specific parts are a tapered threaded port on the water pump (and engine block) of B Series diesel engines, but the question is a general one. It relates to parts from Toyota with the 6th and 7th numbers '52'. So, for example:

90345-52001 - this is a tapered blanking plug which is used on the water pump (no ACSD) and as an oil gallery plug on the block of a 3Bii or 14B.
90404-52028 - this is a water outlet union which connects the water pump to the ACSD on a 14B.

The plug mentioned above is used on dozens of different Toyota models.

I have a 'G1/4-19' parallel (bottom) tap, which I believe is a BSP thread. It's 19 TPI (not the 18 TPI of the American NPT system). But I cannot get the tap into the tapped hole on a 14B water pump. The shank of the tap will fit snugly down the tapped hole, but I cannot get the tap threads in.

Could anyone suggest what's going on here? Is the hole perhaps indeed 1/4"-19 TPI but made with a tapered tap?

Or is there another tapered tap system which is very similar.

The reason I want to know is that I wish to tap out a temperature sensor hole on my water outlet to accept the above mentioned water outlet union to connect a turbo coolant bypass hose.

Thanks!

 

[AirheadNut]

From what I can tell the G1/4-19 tap is a BSPP thread, whereas Toyota uses BSPT thread. The tap you have is parallel thread, the hole will be a tapered thread. What’s the difference between BSPP and BSPT? - QC Hydraulics - https://www.qchydraulics.com/whats-the-difference-between-bspp-bspt.html

 

[TheBussman]

Everything Toyota I've run into so far and most other jap equipment has been BSP. They would have in fact used a tapered tap and not a standard tap. The way to know for sure is to try the outlet union on a 1/4bsp die. Get a 1/4 BSP tap it and should work well.

 

[Eurasiaoverland]

From what I can tell the G1/4-19 tap is a BSPP thread, whereas Toyota uses BSPT thread. The tap you have is parallel thread, the hole will be a tapered thread. What’s the difference between BSPP and BSPT? - QC Hydraulics - https://www.qchydraulics.com/whats-the-difference-between-bspp-bspt.html

I think you're right on the money, thanks! The question now is whether a parallel tapped 1/4" BSPP hole will seal a tapered 1/4" BSPT union with thread lock. I would guess it will be OK as the system is barely above ambient pressure. Or should I get a 1/4" BSPT tap to be sure?

 

[AirheadNut]

I would go with a tapered tap just to be on the safe side, but then I'm fairly particular about threads matching up right.

 

[TheBussman]

if your straight tap wont start in the factory made hole where that union usually goes then you need a tapered tap, don't want to make it too big and then not be able to tighten it up.

 

[mudgudgeon]

I think you're right on the money, thanks! The question now is whether a parallel tapped 1/4" BSPP hole will seal a tapered 1/4" BSPT union with thread lock. I would guess it will be OK as the system is barely above ambient pressure. Or should I get a 1/4" BSPT tap to be sure?

It's not best practice, but should still be ok.

If you're in a hurry, use thread tape or paste, and bolt it up.

If you're not in a hurry, buy a tapered tap.
Might cost you $20-30+shipping