Help Identifying "Funny" Pipe Thread, Please ?

[alan_fincher]

I'm still struggling with trying to get a correct take off from my BMC 1800 cylinder head, to feed a calorifier.

 

I've been sent two different parts, one definitely wrong, and the second only a dubious fit.

 

I've been given the runaround by two parts suppliers.

 

I believe (probably) that the British BMC 1500 and BMC 1800 use a different thread, but also that the Turkish BMC 1800 is different also. Also it appears possibly that my British 1800 has been rebuilt with a 1500 head.

 

All I have is the threaded plug that was in the hole, which has been mangled at some time in the past, and is hard to measure accurately.

 

I don't think that the thread in the cylinder head is either 3/8" BSP (19 TPI) or 3/8" NPT (18 TPI). It's about the right diameter for one of these 3/8" threads, but so far as I can see is coarser, at maybe only 17 threads per inch.

 

Can anybody please either.....

 

1) Tell me the thread(s) used on this engine (British BMC 1800)

or

2) Point me at a reliable reference that allows me to translate a diameter and number of threads per inch into what type of thread it is.

 

Ideally I'm looking for a 90 degree elbow to screw directly into the head, as a straight one is raising the pipe higher than the water in the header tank, leading to an air-lock situation.

 

Many thanks,

 

Alan

[OptedOut]

One for starters.

 

http://en.wikipedia.org/wiki/ISO_228

 

Some metric.

 

http://sixmm.com/tech/tict.htm

 

Edit: Get a thread guage and find the thread angle, 60 degrees is metric, 55 degrees BSP etc.

 

17 TPI is 1.5 mm pitch

Edited December 1, 2008 by OptedOut

[Iain_S]

17 TPI is 1.5 mm pitch

 

3/8" is 9.525mm. Could it be 10mm, ISO metric coarse?

 

Iain

[alan_fincher]

17 TPI is 1.5 mm pitch

Thanks....

 

But is there a thread where the OD is about 15.5 mm (0.610") with a 17TPI thread (pitch 15mm, as you say or 0.0588").

 

I can't find one, hence the question!

 

Alan

[Iain_S]

Thanks....

 

But is there a thread where the OD is about 15.5 mm (0.610") with a 17TPI thread (pitch 15mm, as you say or 0.0588").

 

I can't find one, hence the question!

 

Alan

 

M16 ISO metric conduit is 1.5mm pitch.

 

Iain

[bag 'o' bones]

Up tot he 1960's british car manufacturers used BSF (British Standrad Fine) after that there was a mix of BSF and the American UNF.

 

To be honest there were a lot of different thread standards being used at the including the old 'Whitworth' threads.

 

I'm no expert so do what I do buy samples of a load of different bolts that are about the same thread/width and have a 'fitting' session.

[OptedOut]

Your figures of 15.5 mm and 0.610" probably mean 16 mm and 5/8" as the thread is usually truncated or radius at top.

[David Schweizer]

Edited:- to remove reply as I mis-read the original post.

Edited December 1, 2008 by David Schweizer

[Timleech]

I'm not intimately familiar with the various forms of BMC diesels, but 5/8" UNF is a common one for the likes of temperature gauge fittings, is that the takeoff that you're trying to use?

 

Tim

[OptedOut]

but 5/8" UNF is a common one for the likes of temperature gauge fittings, is that the takeoff that you're trying to use?

 

Very near at 18 TPI, considering the initial doubt of actual TPI.

Edited December 1, 2008 by OptedOut

[alan_fincher]

Hi all,

 

Thanks for all your thoughts.

 

I't's entirely possible I'm out by one on the TPI. I'm trying to measure from the blanking bolt that was in the hole, there are a maximum of 6 turns I can measure across, and it's been highly manked up.

 

It's almost certainly been in the head since at least 1995 when Calcutt rebuilt the engine, as the green paint seal was undisturbed,

 

It looks like it's been crushed in a vice or mole grips several times, and then attacked by a hammer. I can't imagine why, unless it was to try and make it grip when it wasn't before.

 

I'm quite nervous of how badly the internal thread in the head may be damaged.

 

I must admit I can't see why a pure metric thread may have been used on an early 1970s British engine, but I suppose anything is possible.

 

It's not in the temperature sender hole. It's on an upward opening hole in the cylinder hear, at the rear in one corner, and so tight that it only just clears the rocker cover, making it even harder to get on and off, (it already fouled the castings on the Polar heat exchanger. ).

 

I'll try and grab some pics later, as I also have a problem with it air locking.

 

I'm waiting for Calcutt to exchange the part for an alternate one, so fingers crossed it may fit better.

[bottle]

Of no real help to Alan but the outlet he is trying to use is the 'heater' outlet.

 

I suspect that an MG (car) parts supplier may help (if all else fail) but I cannot remember if they used a straight take off or a bend.

[churchward]

I must admit I can't see why a pure metric thread may have been used on an early 1970s British engine, but I suppose anything is possible.

 

There wouldn't a metric thread originally. BMC leyland on their engines used AF/UNF thread sizes. However, there is no telling what a subsequent rebuilder may have done.

[alan_fincher]

Of no real help to Alan but the outlet he is trying to use is the 'heater' outlet.

 

I suspect that an MG (car) parts supplier may help (if all else fail) but I cannot remember if they used a straight take off or a bend.

Yes, Thanks Keith.

 

I've posted this before, but this identifies the tapping I'm trying to use....

 

 

Here's one that someone kindly posted of their boat with a calorifier attached...

 

 

I need to achieve something similar, although my pipe needs to run forwards, not backwards.

 

The level in the header tank only starts off about half full (to allow for expansion), so if the pipe is hooked over that, (near the large rubber connector), then it's higher than the coolant level, so hard to get free of air.

 

All ideas much welcomed, as I am out of them!

 

Alan

[Hairy-Neil]

I suspect that an MG (car) parts supplier may help (if all else fail) but I cannot remember if they used a straight take off or a bend.

 

IIRC the heater outlet elbow on an MGB head is a flange with 2 bolts. It goes into the side of the head, adjacent to spark plug No.3.

 

There wouldn't a metric thread originally. BMC leyland on their engines used AF/UNF thread sizes. However, there is no telling what a subsequent rebuilder may have done.

 

They maybe did for nuts, however, UNF was far from universal on BMC engines. The drilled and tapped holes into cast iron block or head where studs fitted were all UNC and the spark plug threads on the petrol version of the B series were 14mm.

Edited December 1, 2008 by Hairy-Neil

[churchward]

IIRC the heater outlet elbow on an MGB head is a flange with 2 bolts. It goes into the side of the head, adjacent to spark plug No.3.

 

 

 

They maybe did for nuts, however, UNF was far from universal on BMC engines. The drilled and tapped holes into cast iron block or head where studs fitted were all UNC and the spark plug threads on the petrol version of the B series were 14mm.

 

Agreed, UNF was not a universal std but really I was saying that Metric would not have been used originally. BMC used a mixture of thread stds on the engine and bodywork throughout the car but none of it was metric post war. A Morris Minor (in BMC era) for example uses at least 4 thread stds MG B and Midget will be much the same. None of them is Metric. Oddly enough (to digress a moment) Morris did use a long defunct metric std pre-WW2 in some situations.

 

I rather suspect that the whole Alan has highlighted was indeed originally tapped UNC. However, as I said there is no accounting for how sloppy subsequent rebuilds my have re-drilled/tapped the hole or even fitted a helicoil to rethread to a different std. The hole was indeed part of the heater take off. I can't remember on a B series type engine if it would have been tapped at all as on an A series it would have had two studs either side of a smooth bore for a heater valve to be fitted.

Edited December 1, 2008 by churchward

[David Schweizer]

I don't know whether it helps but hereis a photo of my BMC 1'5 (built in 1981) the water take off pipe is vclearly shown on the l/h side at the rear of the head, it is definitely fitted intop a threaded hole.

 

http://www.canalworld.net/forums/index.php...=si&img=799

 

If you are unable to get a definitive identity of the thread size, I can ask the Engineer who re-built my engine if he knopws what the standard thread size should be.

[alan_fincher]

I don't know whether it helps but hereis a photo of my BMC 1'5 (built in 1981) the water take off pipe is vclearly shown on the l/h side at the rear of the head, it is definitely fitted intop a threaded hole.

 

http://www.canalworld.net/forums/index.php...=si&img=799

 

If you are unable to get a definitive identity of the thread size, I can ask the Engineer who re-built my engine if he knopws what the standard thread size should be.

Ha!

 

You only posted that to show off your pristine rebuilt engine, versus my work weary lump with peeling paint!

 

Actually I've seen your picture before, David, and it appears that what's been screwed into the head is a 90 degree elbow of the required thread.

 

That's exactly what I'd like to do, if I could get the parts.

 

Two observations though.

 

1) I've been led to believe that the thread may differ between 1500 and 1800, (although equally there is more than a lingering doubt that my 1800 engine may actually have a 1500 head on it!)

 

2) You appear to have a Bowman, rather than a Polar header tank. To me these have the advantage of both sitting higher, so it's easier to keep the whole calorifier hose below the coolant level, as well as not encroaching so tightly on the rocker cover, (which is a pig to remove and refit on mine, as it will not easily pass the "lumps" on the side of the Polar).

 

I will crack this, but oh the joys of a 30 or 40 year old engine!

 

 

I rather suspect that the whole Alan has highlighted was indeed originally tapped UNC. However, as I said there is no accounting for how sloppy subsequent rebuilds my have re-drilled/tapped the hole or even fitted a helicoil to rethread to a different std. The hole was indeed part of the heater take off. I can't remember on a B series type engine if it would have been tapped at all as on an A series it would have had two studs either side of a smooth bore for a heater valve to be fitted.

This is indeed possible.

 

I don't know the history of my engine before a 1995 rebuild, so it could have come from an application like a van, where a cab heater was fitted, in which case the hole was plugged at marinisation.

 

Or it may have been an industrial unit on a generator set, or pump, or something where it never needed to heat anything, so the plug "could" be original. However despie the criticism heaped on BL, I doubt even they would have fitted quite such a mangled part as I removed, (I'll picture it later).

 

A further confusion is that a manual for the BL engine shows a thermostat housing with a second take off, implying that in some applications a heater feed was connected there, rather than directly to the head. It's never simple!

[churchward]

This is indeed possible.

 

I don't know the history of my engine before a 1995 rebuild, so it could have come from an application like a van, where a cab heater was fitted, in which case the hole was plugged at marinisation.

 

Or it may have been an industrial unit on a generator set, or pump, or something where it never needed to heat anything, so the plug "could" be original. However despie the criticism heaped on BL, I doubt even they would have fitted quite such a mangled part as I removed, (I'll picture it later).

 

A further confusion is that a manual for the BL engine shows a thermostat housing with a second take off, implying that in some applications a heater feed was connected there, rather than directly to the head. It's never simple!

 

One solution if the thread is knackered (whatever it is) is to drill and tap to the next size up that matches a bolt/fitting you can find or a helicoil. Although in that case (helicoil) it is more of a specialist activity (and can be expensive) unless you are familiar with them as getting it right so that it doesn't leak is key.

 

As you say I doubt BL would have made a mess of it. Ok some things may have got thrown together but normally their engine engineering is sound and the B series petrol or diesel is a robust unit and being an old design is almost infinately maintainable/rebuildable as indeed is the A series.

Edited December 1, 2008 by churchward

[alan_fincher]

Slightly tongue in cheek, but I almost wonder if I couldn't Araldite, (or similar), a fitting in.

 

Unlike other tapped holes on the engine, it's not something that would ever need to be removed again.

 

I think it's soluble without such a cowboy solution, but if I found the threading incapable of holding anything in in a watertight way, I might consider it.

[Denis R]

One solution if the thread is knackered (whatever it is) is to drill and tap to the next size up that matches a bolt/fitting you can find or a helicoil. Although in that case (helicoil) it is more of a specialist activity (and can be expensive) unless you are familiar with them as getting it right so that it doesn't leak is key.

Looking at the photo it appears that the face is machined, so it should be possible to fit a helicoil and then assuming you use a fitting with a parallel thread, use a Dowty washer to make the seal between the hex of the fitting and the head face.

[churchward]

Slightly tongue in cheek, but I almost wonder if I couldn't Araldite, (or similar), a fitting in.

 

Unlike other tapped holes on the engine, it's not something that would ever need to be removed again.

 

I think it's soluble without such a cowboy solution, but if I found the threading incapable of holding anything in in a watertight way, I might consider it.

 

I doubt the araldite will hold due to vibration. It would be simple thought to re-tap to another size of thread and there should be enough metal around the hole to do this as long as you can get a fitting to screw into the result. Another thought would be to "clean" the existing thread up a bit by using a tap of the present size and std. This will take off any cross-threading burrs and may help the thread key better to whatever you are going to screw into it.

 

Looking at the photo it appears that the face is machined, so it should be possible to fit a helicoil and then assuming you use a fitting with a parallel thread, use a Dowty washer to make the seal between the hex of the fitting and the head face.

 

True, the surface is a flat machined one so coudl be sealed in this way but unless one needed to restore to a specific thread size at or less that the present hole just drilling and re-taping is easier and less expensive I would think.

[Batavia]

Slightly tongue in cheek, but I almost wonder if I couldn't Araldite, (or similar), a fitting in.

 

Unlike other tapped holes on the engine, it's not something that would ever need to be removed again.

 

I think it's soluble without such a cowboy solution, but if I found the threading incapable of holding anything in in a watertight way, I might consider it.

 

You could certainly do this with one of the Belzona 1000 series compounds (1111 is the one we use for most applications) - perhaps drill the hole out, make good with Belzona and the re-tap with a sensible thread.

 

Chris G

[Big Steve]

In all the tables I've seen the only thing that comes near you thread is UNF, and even that isn't very close.

 

Here's a link to the site I use for stuff like that.

 

http://www.alanstepney.info/page74.html

 

I've got one of these engines in the shed, I'll get it out tomorrow and have a look.

[alan_fincher]

I could easily be out by 1 on the count of threads per inch.

 

Also the plug I took out hasn't really got any point where the threads are undamaged on opposite "sides", so it could easily be meant to be a larger diameter than my calipers are telling me.

 

Where would I have to go to get hold of "plumbing" with a UNF thread, please, as it could be worth a try.