Oilway plugs in sump - thread please

[Ruairidh Dunford]

More on this subject here: http://pub25.bravenet.com/forum/static/s...6&cmd=show

[Chris KC]

Bob, Zeto, thanks. And Ruairidh - thanks for finding this! David Cochrane recalled there was a thread (no pun intended!) on the topic but I had failed to find it.

For what it's worth:
The steel plugs I have taken out (3 brg engine) are definitely 28 tpi - yes it's hard to count accurately, but if you offer up to a 1/8 BSP tap under a magnifying glass the peaks coincide exactly.

As to whether they are parallel (BSPP) or tapered (BSPT), the taper angle of BSPT is 1:16, and it is harder still to judge whether the thread diameter drops off by 1/64" (0.4mm) over a quarter inch of worn thread. However, apart from a slight lead in on the first thread, I see no sign of a taper whatsoever (when offered up between the jaws of vernier calipers under a magnifying glass). My bet then is 1/8 BSPP.

Dave Mann made a valid point above - BSPP is not self-sealing and should normally be backed up with a ring seal, whereas BSPT tightens into the taper until it seals. I'm not sure this is significant given the oil pressure concerned and that any drips will only migrate back to the sump.

And just to re-iterate what I said above - I contacted one (Chinese) eBay seller to confirm whether their BSP screw was parallel or taper thread, and they replied oops sorry it's NPT, which as Bob rightly points out has a different thread angle. As others have said this may not be important - but buyer beware.

[Steve Jones]

Rather than buy such things on Ebay or wherever from unknown sources, try your local hydraulic supplier. Most towns have one and you'll find the people there understand what BSP, BSPT NPS etc. etc. is all about. The one local to me https://www.mendahose.co.uk/ have never failed to supply whatever fitting, union or plug that I wanted from stock and are happy to spend a bit of time making sure it's what I'm after. Try that on Ebay!

Steve

[Chris Garner]

As Chris says, counting small thread pitches can be difficult. Investing in an internal / external screw pitch gauge is a good idea and can be bought cheaply for around a fiver.

[Chris KC]

Steve that turned out to be jolly good advice! My local hydraulic / pneumatic supplier handed me half a dozen stainless 1/8" BSPP fittings and wouldn't take any money for them... Only required quickly dressing to length with a grinder.

I will pop them in with Loctite 242, which last time I looked was the lowest strength thread lock/ sealant in their catalogue.