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Lanchester radiator cap - thread identification

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ranald
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Lanchester radiator cap - thread identification

Post by ranald » Wed Jul 11, 2018 10:12 am

Hello, Does anyone have any thoughts on the likely thread used on a 1932/3 Lanchester 15/18 radiator? It is 2 7/16 inches in diameter. Could it be BSW? Thank you, Ranald
Radiator (2).JPG

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Vortex O'Plinth
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Re: Lanchester radiator cap - thread identification

Post by Vortex O'Plinth » Wed Jul 11, 2018 11:59 am

I would think the thread probably is Whitworth form but is more likely to be a BSP size. (BSP follows the BSW thread form). Can you check the threads per inch? If it's 11 then the thread is likely BSP, although your 2 7/16" major diameter doesn't match any standard BSP size. Is this a measurement with a rule? If so a check with a caliper gauge might be more accurate.
Nick

Pas d'elle yeux Rhône que nous.

ranald
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Re: Lanchester radiator cap - thread identification

Post by ranald » Wed Jul 11, 2018 5:31 pm

Thanks Nick for your reply. It is 11 tpi. I've checked the diameter and it is 2 7/16" (61.9mm).

AlanCoombs
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Re: Lanchester radiator cap - thread identification

Post by AlanCoombs » Wed Jul 11, 2018 10:39 pm

Hi Ranald,

I know that this one will cause a great deal of disbelief, even outrage, but here it is:
It's metric, M62x2.0mm; I've just measured mine to confirm.
You'd be right to not believe that anything original in an all-british car from the early thirties would be metric - most threads are indeed BSF/BSW/BSP/BA, even a few oddball BSBs thrown in, but there are a handful of parts originally specified in metric, mostly in the engine internals (bore, stroke, gudgeon pins, journal diameters, valves, etc.), plus in the worm-drive axle, and now the matching threads on the fuel filler and radiator cap. If you offer up an 11tpi BSP thread for comparison, you'll find that the thread pitch on the radiator is actually noticably finer.

Incidentally, somewhere I have a spare cap from an LA10 - which is the same bakelite-over-brass construction, but has a smaller diameter than that on the 15/18. I wanted to measure it up to see what thread that was, but I can't find it - I must have tucked it away somewhere when I realised it didn't fit, and I've long since forgotten where; maybe somebody else similarly geeky when it comes to vintage threads with a 10 would care to measure one!

Best regards,
Alan

ranald
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Re: Lanchester radiator cap - thread identification

Post by ranald » Thu Jul 12, 2018 8:40 am

Thanks for clearing that up Alan. Another metric thread on the 15/18 is found on the wheel studs / nuts (M14 x 1.5mm).

Marcel Renshaw
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Re: Lanchester radiator cap - thread identification

Post by Marcel Renshaw » Fri Jul 13, 2018 7:20 am

Why not metric after all it was invented by an English man .

chrisjb
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Re: Lanchester radiator cap - thread identification

Post by chrisjb » Fri Jul 13, 2018 12:57 pm

In 1897 the Lanchester brothers considered that the standard Whitworth "BSW" thread was too coarse for cars, the nuts would vibrate off. So they developed their own 'M' thread which preceded the BSF thread by about 10 years. It did have some "metric" in the range when they filled in the gaps. For example 5/16" is 8mm and from memory a metric nut fitted. I don't know what the M stood for.
Appendix B in Lanchester Motor Cars by Anthony Bird and Francis Hutton-Stott goes into more detail with comparison tables.
Chrisjb

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Vortex O'Plinth
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Re: Lanchester radiator cap - thread identification

Post by Vortex O'Plinth » Fri Jul 13, 2018 1:31 pm

Just as an aside, my '48 MG TC has an 'XPAG' engine, a design cribbed from Hotchkiss that had been bought by William Morris. The almost universal screw thread system in use on British cars in those days was Whitworth, both BSW and BSF. The Hotchkiss design being of continental origin, used metric fastenings throughout. In order to minimise the re-tooling necessary Morris retained the metric threads throughout the engine, but conscious that MG owners would not want to have to acquire metric spanners in addition to the Whitworth ones for use on the rest of the car, MG produced unique screws and bolts with metric fine threads and Whitworth hex. heads. Many MG's - and Morris's - from this era have survived to this day, but as one can imagine, mechanics and amateur restorers unfamiliar with this engineering quirk have over the years have managed to force standard BSF bolts down metric threaded holes with unfortunate effects.
Nick

Pas d'elle yeux Rhône que nous.

AlanCoombs
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Re: Lanchester radiator cap - thread identification

Post by AlanCoombs » Sat Jul 14, 2018 10:48 pm

Thanks for that, although we seem to have gone a bit off-topic! I knew I had read about the Lanchester M-threads somewhere, but had entirely forgotten where, but yes, the table in B & H-S explains all. Next time I'm finding that 5/16 is just too small but 3/8 too large, I'll know that once again, FWL got there first.

Incidentally, on a similar theme, if you find that you like the nice Lanchester logo on the wheel nuts on the left-hand side of the car, but want to get rid of the nasty Rolls-royce logo on the right-hand side with Lanchester logos on both sides, then a bit of brute force and a few seconds with an air impact wrench works a treat*

Alan


*Please don't actually try this!

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