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healeyboz

healeyboz

Jedi Knight
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a threaded piece that I can insert into the top of the new radiator that will allow for the thermostat to mount properly. The old readiator had a smaller hole inside that pushed the sensor tight to the nut. NOT THIS ONE!!

Anyone know what size threads these are?
 
The threads (i think) are 1/4" BSPP.
 
Barry,
Are you referring to the threaded “nipple” just around the side of where the upper hose attaches?
If you are, and you’re talking about the temp sensors end and it’s compression sleeve, the threads are 5/8-18. What do you mean by the old radiator had a smaller hole inside? What is this one not doing? Is the nut not screwing in enough? “or” is the sensor not going in all the way now?

dug
 
Hey Dug,

THanks for the thread size. The sensor hangs "loose" inside the nut to allow the nut to turn and tighten to the radiator. There is a smaller hole that the sensor slides into and stops it from sliding all the way into the radiator. Does this make sense?

I am wondering if there is some type of fitting out there that has the 5/8-18 male to fit in the rad and the same thread female for the sensor nut, but has some sort of restriction for the sensor to push against.
 
Kind of the same type of thing that allows you to hook the sensor to the head directly but with the same size male threads as the female threads.
 
Sensor pushes against nothing, it just stickes out in the radiator.
 
Now Jack,

If you look through the threads of where the sensor goes in the diameter is smaller than the threads. The sensor pushes against this to create a seal against the nut that is wrapped around it.
 

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OK guys... I am almost 95% positive it is NOT 5/8-18. You can force 5/8-18 (I've done it), but it is almost certainly BSPP.
 
I noticed this bit of information on the Pegasus site, (Note: 5/8-18 and 3/8 BSP are hard to tell apart. A 3/8 BSP fitting has a .66" OD and will not quite fit in a 5/8-18 hole; a 5/8-18 fitting will be loose in a 3/8 BSP hole.) Sounds like Trevor was right, 3/8 BSP
Pegasus also has adaptors for this thread available I believe.
 
I can't remember if it is 3/8 or 1/4, but I believe it is 19 threads per inch.
 
Good link, the adapter shown even calls it out as 5/8-18. If someone else has a spare one of these, take it to someone with a thread pitch gage and have them check the pitch and measure the OD. You might find them to be 18 threads per inch with an OD of 0.62. Look in any machinist handbook and you will see that BSPP and BSP are 19 threads per inch. The adapters have roughly 3/8" of male thread so it a close call. All and I mean all of these that I have pulled from heads have measured with an OD slightly smaller than 5/8”.
I use BSPP in my work, having both taps and using them very commonly leads me to stay with 5/8-18. BSPP is used in some vacuum cups; the packaging industry uses them for pick and place of product. A BSPP would be very tight indeed. Hey call or email the guy’s in the link, what do they say?
Dug
 
I've argued this several times, and I do not think that we've ever reached a definitive verdict. Or maybe we have and I've refused to admit defeat. :wink:
 
From everything I've read (no first hand experience at this) British Standard Pipe, (BSP) threads, are used for the liquid connections in Sprites and match NO KNOWN threads anywhere else in the world. .. Aren't the BSP in the oil pan and diffy plug as well?
 
I think that the threads on the temp bulb fitting are straight pipe thread not tapered so as to press the ridge on the bulb tight on the gland washer. The diff ,oil ,trans are tappered.
 
Yes they are straight, but are they 5/8-18 or 3/8"BSPP.
 
Trevor Jessie isn't wrong! I'm forced to agree with him about the threads being BSP. According to this web page there are two forms of BSP, both tapered and straight. The straight threads need a shoulder and sealing washer to seal, the tapered threads are like our US pipe threads, self sealing by interference fit. I know the temperature sensor in my engine used a tapered thread from the adaptor into the engine and a straight thread for the gland nut that held the bulb in place. I see on the chart that the thread pitch is indeed 19 turns per inch as Trevor said, not the 18 tpi common to US pipe thread. https://www.newmantools.com/taps/bsp.htm
Bill L. is right on, most likely all the plumbing fittings of this type on a Spridget are BSP.
 
Ok,
Then who else has a 3/8 BSPP tap that they can attempt threading into a spridget head or MKI-MKIII radiator? (A series "or" spridget only) I would be very interested to know if they can even start it. I have both a tap and straight BSPP threads that let me try this in both heads and radiators. This combined with the OD measurement of several adapters all measuring just under 0.62 in diameters lead me down this unpopular path.
Both 3/8” BSPP and 5/8-18 have the same tap drill callout in most all drill / tap charts (37/64).
The “thread pitch” of a 3/8 BSPP is 0.0526 tip to tip and a 5/8-18 is 0.0555. In 3/8” (the average length of the threaded adapter’s male threads) that’s a difference of 0.0029. The OD is part of the key.
dug
This is a good (pardon the pun) thread!
 
OK Dug,

Are you saying that the 5/8-18 tap works fine, but the BSPP tap won't even start? If so, then we've settled this... right?
 
BTW, what is the major diameter on 1/4" BSPP threads?
 
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