Honda oil pressure switch thread

rivvybarner · L Plate Warrior Joined: 15 Mar 2012 Karma :

I've got a Bros 650 where the P/O has broken the original proud mounting - I need to retap the hole but cant seem find out the correct thread. Does anyone have any idea what tap I'm looking for
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puddin' chips and gravy please...

Andy Perrett · Crazy Courier Joined: 07 Oct 2021 Karma :

Does your tap and die set not have a small set of toothed gauges to check?

I'd want to know for sure rather than guesses on the Internet, before rethreading it.

If you've not got one, get one for under a fiver. Thumbs Up

rivvybarner · L Plate Warrior Joined: 15 Mar 2012 Karma :

not got one yet - I've never needed to retap anything before, but I thought I'd check before I went shopping.
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puddin' chips and gravy please...

MCN · Super Spammer Joined: 22 Jul 2015 Karma :

That's an NPT (National Pipe Thread USA standards) thread. NPT uses a tapered profile to augment sealing properties. (BSP (British Standard Pipe) uses a parallel profile.)

But I would need a banana next to it to guess the size.

NPT (most pipe threads) use the inside diameter of the pipe it is used on as the description size.

e.g.
1/8" NPT is for pipes/tubes with inside diameter of 1/8" ("= Inch).
1/4" Baptist for pipes with inside diameter of 1/4".

Nominal sizes. 1/8, 1/4", 3/8", 1/2", 5/8" and so on.

Taps and Dies easily available in U.K. eBay/Bezozon and smaller specialist engineering suppliers.
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Disclaimer: The comments above may be predicted text and not necessarily the opinion of MCN.

Islander · World Chat Champion Joined: 05 Aug 2012 Karma :

rivvybarner · L Plate Warrior Joined: 15 Mar 2012 Karma :

cheers chaps for the input - most welcome and appreciated.
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puddin' chips and gravy please...

WD Forte · World Chat Champion Joined: 17 Jun 2010 Karma :

1/8th npt is what I've found on Honda oil pressure switches
I think I still have a tap somewhere.
Remember its a tapered thread so don't go mad
and over tighten them or it's tears before bedtime.
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bikers smell of wee

Polarbear · Super Spammer Joined: 24 Feb 2007 Karma :

steve the grease · Crazy Courier Joined: 26 Jan 2018 Karma :

I have to say I find it most odd that the Japanese would use a thread sized in inches, when they have been totally metric since the war ( maybe before?), and there are plenty of metric sizes to go at, but NPT it may be . Here is a list I kept that I thought would be useful. Part numbers are Intermotor - available at any motor factors.
"Here are the complete range of oil pressure switches
Part No. A/F Size Thread Pressure ( p.s.i.)
51150 24 1/8" BSP Taper 0.7-2.2
50820 22 1/8" BSP Taper 2.2-3.6
51140 22 1/8" BSP Taper 3.0-5.0
50750 22 1/8" BSP Taper 3.0-5.0
51100 22 1/8" BSP Taper 3.0-6.0
51110 22 1/8" BSP Taper 3.0-6.0
50740 22 1/8" BSP Taper 3.0-6.0
50810 22 1/8" BSP Taper 3.0-6.0
50700 22 1/8" BSP Taper 4.5-7.5
50800 22 1/8" BSP Taper 4.5-7.5
51196 24 1/8" x 27 NPTF 1.26-3.25
51010 22 1/8" x 27 NPTF 2.0-5.0 N.O.C.
51011 22 1/8" x 27 NPTF 2.9-7.3 N.O.C.
51000 22 1/8" x 27 NPTF 3.0-5.0
50620 13 1/8" x 27 NPTF 3.0-5.0
50530 22 1/8" x 27 NPTF 4.4-8.7
50540 22 1/8" x 27 NPTF 4.5-7.5
51060 22 1/8" x 27 NPTF 4.5-7.5
50670 22 1/8" x 27 NPTF 4.5-7.5 N.O.C.
50500 22 1/8" x 27 NPTF 5.8-10.2 - Standard sprite
51020 24 1/8" x 27 NPTF 6.5-8.5 N.O.C.
50650 22 1/8" x 27 NPTF 6.5-10.0 N.O.C.
50630 13 1/8" x 27 NPTF 10.0-13.0
50610 25.4 1/4" x 18 NPTF 2.0-8.0
50850 22 1/4" x 18 NPTF 2.9-5.1
50590 22 1/4" x 18 NPTF 2.9-8.7
51050 22 1/4" x 18 NPTF 3.0-5.0
50690 22 1/4" x 18 NPTF 4.5-7.5
51190 22 1/4" x 18 NPTF 7.5-11.9
50510 22 1/4" x 19 NPTF 2.9-5.1
50520 22 3/8" BSF 6.1-10.2
50680 22 3/8" BSF 17.4-29.0
50611 22 1/2" UNF 3.0-5.0
51170 22+18 1/2" UNF 4.5-7.5
50600 22 1/2" UNF 5.8-10.2
50950 22 M10 x 1 2.2-6.5
51031 22 M10 x 1 5.8-10.2 N.O.C.
50660 22+15.8 M10 x 1 7.5-10.0
50760 22 M10 x 1 7.5-10.0
51030 22 M10 x 1 17.4-23.2 N.O.C.
50970 22 M10 x 1 23.0-29.0 N.O.C
50960 22 M10 x 1 Taper 2.2-6.5
51197 24 M10 x 1 Taper 4.25-6.25
50550 22 M10 x 1 Taper 4.4-8.7
51015 22 M10 x 1 Taper 4.4-8.7
50710 22 M10 x 1 Taper 4.4-8.7
50951 24 M10 x 1 Taper 4.4-8.7
51040 22 M10 x 1 Taper 23.0-29.0 N.O.C.
50720 22 M12 x 1.5 0.7-2.2
50570 22 M12 x 1.5 2.9-7.3
50730 22 M12 x 1.5 2.9-7.5
50725 24 M12 x 1.5 4.25-6.25
50910 22 M12 x 1.5 5.5-8.5
50770 22 M12 x 1.5 6.0-8.0
50780 22 M12 x 1.5 7.5-10.0
50790 22 M12 x 1.5 7.5-10.0
50830 22 M12 x 1.5 7.5-10.0
51195 24 M12 x 1.5 Taper 4.25-6.25
50890 22 M12 x 1.5 Taper 5.8-10.2
50900 22 M12 x 1.5 Taper 7.5-11.5
51131 21 M14 x 1.5 2.0-4.0
50985 21 M14 x 1.5 2.0-4.0
50980 22 M14 x 1.5 2.2-3.6
50990 21 M14 x 1.5 3.5-6.5
50721 24 M14 x 1.5 3.5-6.5
51133 21 M14 x 1.5 4.25-6 25
50930 22 M14 x 1.5 4.4-8.0
50935 22 M14 x 1.5 4.4-8.0
50840 22 M14 x 1.5 4.5-7.5
50860 24 M14 x 1.5 5.8-8.7
50560 22 M14 x 1.5 7.3-11.6
50880 22 M14 x 1.5 8.0-11.0
51134 21 M14 x 1.5 28.0-32.0
50870 22 M16 x 1.5 5.8-10.2
50871 21 M16 x 1.5 5.8-10.2
50875 21 M16 x 1.5 10.5-14.5
51130 21 M18 x 1.5 4.25-6.25
51132 21 M18 x 1.5 4.25-6.25
50861 21 M18 x 1.5 6.0-8.0
50941 23 M18 x 1.5 8.0-10.0
50920 23 M18 x 1.5 8.5-11.5
50940 23 M18 x 1.5 8.5-11.5

Plenty of choice there then.......
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All the above is my personal opinion, you can see my lips move, but I'm talking out of my arse.
I've been riding, and fixing , bikes for 50 years, in that time the more I learn, the less I am absolutely sure of.....

Islander · World Chat Champion Joined: 05 Aug 2012 Karma :

rivvybarner · L Plate Warrior Joined: 15 Mar 2012 Karma :

Once again chaps many thanks - some quality input there for sure. I'm going to take it VERY easy with lots of lube ( I told her!) - I suspect the PO just kept tightening up the the old switch not realising it was tapered till it broke apart. 'Tis in a bugger of a position to get to but I'm going slow. Cheers All.
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puddin' chips and gravy please...