Topic: oil pressure sender thread size?

[millerza]

78k 750 looking to plug sender hole
Ok, im 98% sure the threads are NOT 1/8NPT. I tried two fittings on two engine cases 1/8NPT doesn't work. So can anybody tell me what they might be?

The sender will fit(fairly well) in a 1/8npt hole but not vice-versa.

[MoTo-BunnY]

I'm almost sure it's 10mm x 1.0T (tapered) but I'm still looking in my notes to see if I can confirm this 100%.    update: yes, this IS correct, 10mm x 1.0T is the closest equivalent to 1/8"NPT

1/8" NPT is like 3/8" x 27 (threads per inch) in actual  (non-plumbing world) measurements and the metric equivalent is REAL close (both have 60 degree thread angles, too). I actually used 1/8"NPT stuff in old VWs many moons ago with oil lines and it sealed up fine, but they have less oil pressure and I was a bit more hillbilly engineering back then, too.. .. he he. It is more the wedging action of the tapered thread that seals the connection rather than the threads themselves, so maybe that's why it worked for me.

Calipers and thread pitch gauges are great and relatively inexpensive tools to have for incidences like this, by the way. 

Also, just so you know, I found a ton of adapters that convert the M10 x 1.0T to 1/8"NPT, depending on what you want to do (though it sounds like you just need a plug) EG:
http://www.dieselmanor.com/dm_products/fittings.asp
https://www.pegasusautoracing.com/productdetails.asp?RecID=1832

[millerza]

sweet thanks moto-bunny,   i half expected a bunch of "IT IS 1/8" answers.  good to know!!

[754]

 I will try to look at one.. Slight chance it is  1/8 NPTSC or F..there is 2 series of straight pipe thread...the c is coupler, the F is fuel. There is a lot of folks dont know these threads exist. I tapped hundreds of them for oil tank fittings.

 The reason we used them, is there were no depth control issues.  Imagine tapping  the sender guage hole on a set of 750 cases, and having to reject the due to thread being to deep !!

[MoTo-BunnY]

Yes, actually measuring it would be the best. I know there are various Japanese only standards too and I was concerned it could be something like that. However, all my Googling brought up a ton of Japanese car forum stuff where there were needing the above mentioned adapters for 1/8"NPT to 10mm x 1.0. Not sure if that would be relevant or not.....

[brooze72]

Japanese manufacturers of hydraulic equipment used to be fond of using a lot of BSPT, almost identical to NPT (with a Brit twist). Maybe that is what it is?

[cougar]

Hey millerza ; I'm liable to get chastized for this. Even though the thread isn't an exact match, I just used the adapters that came with my oil gauge with a careful wrap of teflon tape. Like I said the thread isn't an exact match but it sealed with no problem or leaks for over 2 years now. And without a couple of inches of adapters sticking up from my motor (1976 cb750) . But the choice is yours.   ...cougar...

[23tbucket]

The threads are 1/8" BSPT....1/8" NPT is similar, but has different TPI and angle cuts on the threads.

[millerza]

I ordered 1/8bspt and 10x1, and it was 100% 10x1

[LesterPiglet]

I'm confused. Why would Honda use anything other than metric?

[Duke McDukiedook]

Just get an oil sender unit for a Honda Civic at your local auto parts store- it will work and be at least 50% cheaper.

[buffaloejon]

Yea, unfortunate that you bought adapters already... NPT is just a tapered thread, so interference is the whole point. And as long as you don't remove the (very closely related) 1/8" NPT, it won't cause any problems... just get some teflon tape!!

And autozone around here sells gauges for 15.99 that include 3 feet of tubing and both a 1/8 and 1/4 NPT adapters... so that's the route I'll be going in the near future.

[cb650]

I'm confused. Why would Honda use anything other than metric?

Y are tires in inches?

[MoTo-BunnY]

Yea, unfortunate that you bought adapters already... NPT is just a tapered thread, so interference is the whole point. And as long as you don't remove the (very closely related) 1/8" NPT, it won't cause any problems... just get some teflon tape!!

And autozone around here sells gauges for 15.99 that include 3 feet of tubing and both a 1/8 and 1/4 NPT adapters... so that's the route I'll be going in the near future.

When trying to make car gauges work on a CB you should make sure that:

1. The gauge is of enough pressure to work on these bikes (most car stuff isn't high enough to cover the complete pressure range of a bike with all of the quick spikes in pressure and what not-typical low psi gauge is NOT enough)  and that:

2. It can handle the vibration and aforementioned quick spikes (liquid filled would be best for this)

Also, a 10mm x 1.0T is tapered (like a pipe thread would be).


It sure would be nice if we could get a definitive answer here on what threads these are? Doesn't anyone have good calipers and some thread pitch gauges and can actually measure them? (I do but I don't have any CB sending units to measure right now....lol)  Though I am thinking it's the thread angle that would be the definitive match and difficult to match up with just the typical thread pitch gauge (they are more for measuring the threads per inch/mm and not angle, typically)

[brooze72]

The threads are 1/8" BSPT....1/8" NPT is similar, but has different TPI and angle cuts on the threads.

Thought we had a definitive answer..

PS I concure with his assesment.  I personally have used NPT fittings in BSPT threaded holes with T tape or pipe dope at high pressure (2000 psi or 140 bar) with success, the threads are SO close, you just cannot thread the NPT fitting in as deep as the original, but that too depends on the quality of the original thread cut.

[brooze72]

I'm confused. Why would Honda use anything other than metric?

I think the 60s/70s were a time of transition for Japanese manufacturers.  They were using metric for a lot of things but were maybe trying to cater to other markets or possibly were in the process of developing their own standards, IMO.  I've seen lots of machinery from that era that have a mixture of metric, US standard & British, just to confuse everyone.  Remember the Japanese drive on the left too!  After using the BSPT threads they changed to JIS (Japanese Industrial Standard).  This high pressure taper seal had a 2 degree difference from US standard but with the exact same threading! What a clusterf@$k! I think everything is now metric on new bikes including tires, wish I could afford to buy a new one & find out!  Oh well, 19mm & 3/4", I only need one wrench for that.

[754]

 I did measure a set, they werent metric and 1/8 NPT tap appeared to fit.. will try to look up BSPT tommorrow..is it 55 degree included angle thread form ? You can easily tell a tapered thread with verniers, when you stick the tips in the hole a ways down and tighten, they will rock a bit, straight thread wont.

 I think NPT is used in many countries.
 If tires are metric, then they would not be 17 or 16 or 18 inch..they are actually "Standetric"...

[brandEn]

I plugged mine with an 1/8" BPT fitting bought from McMaster Carr. I bought both the BPT thread and NPT thread and both fit but the BPT fit better. I used this thread for info
http://forums.sohc4.net/index.php?topic=31371.0

[brooze72]

I plugged mine with an 1/8" BPT fitting bought from McMaster Carr. I bought both the BPT thread and NPT thread and both fit but the BPT fit better. I used this thread for info
http://forums.sohc4.net/index.php?topic=31371.0

Ooh, a thread thread!

[MoTo-BunnY]

Kewl-great information! apparently 1/8" BSPT / 28 tpi it is (but 1/8" NPT / 27tpi is pretty darn close)


ADDITIONAL INFO:

[img width= height=]http://farm8.staticflickr.com/7208/6874157612_42b248784b_z.jpg[/img]


sources:
PIPE THREADS (NPT / BSPT)(.pdf file)

METRIC THREADS (.pdf file)


tons of additional information on threads, industrial standards, metals, conversion charts etc. etc. (source of above):

Maryland Metrics Technical Information



Also note that I see several sources that seem to say that BSPT and JIS (Japanese Industrial Standard) pipe threads are the same! (see attached diagram)


I just wanted to make sure we had some solid answers here before folks go stripping out the threads for their sending units! Believe it or not, there is the rare piece of questionable advice to be found on these boards. 

Now I don't feel quite so hillbilly when I put a 1/8" NPT into my old VWs oil sender, back in the day. Apparently it wasn't exactly the thread but close enough to "work" (and it never did leak oil there, but then again with a VW, how can you tell will all of the other oil leaks? he he)

[LesterPiglet]

I'm confused. Why would Honda use anything other than metric?

Y are tires in inches?

Tyres aren't made by Honda who use metric fittings on their bikes.

[cb650]

Many are made in metric countries though.   I think in the day many where made in japan.  i remember the 10" bridgstones on my ct70 where.  Or whatever size they where.
Even Ford tried to do a metric tire but it failed miserably.

[millerza]

I ordered 1/8bspt and 10x1, and it was 100% 10x1

I'm confused. Why would Honda use anything other than metric?

Metric  10MM X 1.0 worked on my 78k.     I could not get NPT or BSPT to work, tape or not.     Just saying.

[754]

 Just for kicks, we should check part # for sender between K1 and K7...

[MoTo-BunnY]

Just for kicks, we should check part # for sender between K1 and K7...

Here ya go, with a '73 CB500 thrown in just for kicks (they are all the same Honda part number!)

hmmmmm...... the pipe thread thread plot thickens..........   (see what I was saying about wanting a definitive answer?!?  lol)


SWITCH, OIL PRESSURE

1969 CB750K
35500-333-014 (replaces 35500-300-000)
35500-333-014 (replaces 35500-333-004)
37240-P13-013


1978 CB750K
35500-333-014    
37240-P13-013


1973 CB500K2
35500-333-014 (replaces 35500-300-000)
35500-333-014 (replaces 35500-333-004)
35500-333-014
37240-P13-013