Lotus Elan

Thread size advice: thermostat housing heater valve port

PostPost by: Sea Ranch » Tue Aug 09, 2016 4:05 am

Greetings,

Searched the forum and found an interesting discussion on BSPT, BSPP and NPT. But so far, no definitive statement on the thread type/size on the Twin Cam's thermostat housing heater valve and temp sensor ports.

Background: my federal Plus 2 came to me with an old Ford heater shut-off valve installed. No leaks. But I'm pretty darn sure it's not British Standard Pipe! Looks like this:

http://www.macsautoparts.com/ford_mercu ... -ford.html

I need to replace it and would like to use something similar, but not happy risking an NPT pipe thread into BSP port, if that's what we're talking about here.

Thoughts?

Thanks,

Randy
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PostPost by: rgh0 » Tue Aug 09, 2016 10:55 am

As far as i am aware all the Lotus components such as head and front chain cover and diff alloy housing have BSP pipe threads. The Ford Components such as block and gearbox have NPT threads.

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PostPost by: Sea Ranch » Tue Aug 09, 2016 4:46 pm

Got it. What I feared. I suppose I could find an adapter to thread in first. What have you done as a shut-off on your Plus 2 Rohan? Any others with slick solutions? :mrgreen:

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PostPost by: Sea Ranch » Tue Aug 09, 2016 5:26 pm

I'm also looking at this MG/Morris part:
http://www.ebay.com/itm/331116067649?_t ... EBIDX%3AIT

Again, hard to source thread sizes, but the people at Moss Motors say it's "5/8" with 20 tpi and it does not look to be tapered. But that's hard for the eye to see . . . The Ford part I've had in there doesn't look tapered either, but all replacements are described as NPT which is almost always tapered.
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PostPost by: elancoupe » Tue Aug 09, 2016 8:03 pm

I have a straight fitting with a nipple type end in the head, a 90 degree piece of hose, and a valve from a 70's era Ford truck. The cable fits right on the valve, perhaps just needs shortened a bit.

This was not my original idea, but was copied from the old Lotus West tech manual.
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PostPost by: RichardHawkins » Tue Aug 09, 2016 9:38 pm

Randy,

I am pretty sure that the two threaded holes on my cylinder head are 3/8NTP. We never know for sure what previous owners may have done or if Lotus changed the spec at different times. BSP and NTP are very close in diameter and only one thread per inch different in pitch.

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PostPost by: Sea Ranch » Tue Aug 09, 2016 10:24 pm

Very similar, agreed. I liked this explanation, online, which also points out the thread angle across the "flanks" of the threads.
http://www.ralstoninst.com/news/story/t ... spt-seals/

In any case, I've been pondering the adapter threaded into the second port on my twink's thermostat housing. It has the temp sensor threaded into it. The adapter is threaded all the way into the port, right up to it's shoulder. This is an indicator that the female threaded port is not a tapered thread at all (see the above link on pipe thread types and comparisons). Further, tapered male fittings do not have a shoulder at the end of the thread, as they do not "bottom" out on anything; rather, they "wedge" into place.

On the other hand, the non-tapered BSPP - British Standard Parallel Pipe - fittings are not designed to wedge at all. The male fitting has a shoulder and uses a seal ring compressed between the male fitting's shoulder and the female port. This is apparently the most common pipe thread system in the UK and Europe. Some pressure gauges apparently have a longer male thread and use a sealing ring in the bottom of the female port to seal against.

In any case, I suspect that the fully seated adapter in my thermostat housing indicates that both ports in the housing are BSPP. Further, the Ford shut off valve I have only threads in 2 1/2 turns before binding. The Ford fitting is nominally 5/8" diameter across the threads and has about 20 tpi; I believe it to be 3/8" NPT.

I am now eyeing the MG Midget/Morris Minor heater shut-off valve; part number 360-400 on the Moss Motors website:
http://www.mossmotors.com/Shop/ViewProd ... xID=120305
The good folks at Moss Motors went and put their hands on this part, eyeballed it and measured the thread. They came up with nominal 5/8" across the threads and about 20 tpi. They also claim it did not look tapered.

So . . . I am wondering now if this apparently most common pipe thread type in UK and Europe - the BSPP - may well be the thread type on the twink thermostat housing, given that it's a British design, and given that the adapter in my engine appears to thread all the way in and seat on it's shoulder. And I am wondering if the MG/Morris threads used on their heater valve may well be the same, given their British origins and given the nominal measurements taken by Moss Motors.

Whew . . . long post, but that's where I'm at currently. On the positive side, the MG/Morris valve is easily obtainable and looks cool. On the down side, MG forums don't rate the valve very highly in terms of how long it lasts before leaking out the knob stem.

Any other thoughts before I'm forced to take a flyer on an MG/Morris valve and try it out in person?? :roll: :mrgreen:

Randy
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PostPost by: Craven » Tue Aug 09, 2016 10:58 pm

Both holes the same BSPT, some people interchange i.e. fit the heater valve in the Temp position allows easy removal of valve.
Pic of adaptor, may not show but it has a taper on right hand side, as you can see is very short and would explain why it is usually screwed right in.
May help
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PostPost by: Sea Ranch » Tue Aug 09, 2016 11:08 pm

Thanks so much, Ron. I'm pretty sure I'm re-building knowledge already out there . . . just hadn't found it yet.

Okay, so the adapter you picture came out of a twink thermostat housing? I agree they may be short and therefore threaded all the way in. Doesn't explain the use of a tapered thread type when BSPP is supposed to be most common. :?

Unfortunately, the adapter for temp sensor in my twink is pretty frozen in place and I haven't yet had the nerve to put serious force on it.
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PostPost by: Craven » Tue Aug 09, 2016 11:21 pm

Yes genuine fitment in a TwinCam from way back. Probably just more cost effective to make both threads the same.
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PostPost by: Sea Ranch » Tue Aug 09, 2016 11:27 pm

Ron, thanks so much. I agree, the two ports are most likely the same, and now you can confirm with that adapter of yours fitting both. Excellent.

Now I just have to find a valve to fit. Don't want to go to an inline valve if I don't have to . . .

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PostPost by: cusword » Wed Aug 10, 2016 8:06 am

I am at work so don't have the information in front of me, but from memory one is BSP and the other is NPT and one is tapered, but I can't remember which. I will check tonight if nobody confirms before then.

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PostPost by: rgh0 » Wed Aug 10, 2016 10:13 am

Both holes in the thermostat housing were straight tapped and BSP originally I believe. Though its hard to assess the lack of an internal taper given the age of the heads and how the threads have changed by having tapered fittings screwed in.

The original Elan heater valve and original temp gauge bulb adapter are both tapered. I am not sure if the plus 2 electrical sender and hose adapter is tapered or not I would need to pull mine out to measure t hem up. The original adapter has short thread length as observed and normally screws all the way in on old heads with the wear and corrosion present on both components.

I wonder if heads made for Cortinas and Escorts that used Ford components for heater and temperature had NPT threads ?

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PostPost by: billwill » Wed Aug 10, 2016 12:35 pm

As far as I am aware both the water valve hole and temp gauge hole were always the same thread.

This describes the trials & tribulations that I had with mine.
lotus-elan-f19/getting-ogu-roadworthy-again-t26101-15.html#p172491
especially
lotus-elan-f19/getting-ogu-roadworthy-again-t26101-30.html#p172633


~~~~~~~~~~~~~~~~
SAS Engineering must know the correct thread, because my old fittings screwed in easily to the new SAS head, so you could contact them.
http://www.sasengineering.co.uk/

You can buy typical fittings at low cost in a plumbers (UK) and then try them to see if they fit easily into the head, some that I bought (which must be BSP thread) did indeed screw in properly.
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PostPost by: Craven » Wed Aug 10, 2016 1:04 pm

Now then! I have on the bench a brand new untouched QED head, these supposedly are made to the original drawings. The hole for the heater valve is tapered BUT the hole for the capillary adaptor is parallel/straight thread. There seems then the possibility of a tapered fitting ( adaptor ) into a parallel hole.
BTW, I also have a cylinder head with a LF serial No, which I understand indicates it was originally fitted to a MK2 Cortina Lotus, this has a capillary adaptor fitted as type seen in Pic.
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