BSA C10 C11 C12

BSA C10 C11 C12 Forum => Technical Section => Topic started by: Steve P on May 23, 2020, 04:07:17 pm

Title: Speedometer threads
Post by: Steve P on May 23, 2020, 04:07:17 pm
Hi all you helpful people.
I'm beginning to see a motorcycle emerging from the pile of bits I'm assembling. It's a 1955 C11G.
Does anyone know what thread is used for the three screws holding the base to the case on a D shaped smiths speedometer?
The diameter of the one remaining screw is 0.107" (2.70mm). Is it 6BA?
Strangely the only nuts that I can find in my 40 year old collection to fit the studs that fix the speedo to the bracket are metric. Did Smiths anticipate the metric system?
Does anyone know if a rubber gasket is used between the case and the glass. If so can they still be sourced or do I stick some silicone sealent in?
Cheers
Steve
Title: Re: Speedometer threads
Post by: Tman on May 23, 2020, 04:11:49 pm
People often quote that Smiths Chrono's etc have metric threads, although the mounting stud threads on one I've just remounted (not BSA) were 1/4BSF.
Title: Re: Speedometer threads
Post by: Steve P on May 23, 2020, 04:28:34 pm
The ones on my speedo do seem a bit too course for bsf
Title: Re: Speedometer threads
Post by: John M on May 23, 2020, 04:49:57 pm
https://journeymans-workshop.uk/baandme.php

As per above link the BA series were a form of metric thread. Don't know whether this helps or causes more confusion.  :-\
Title: Re: Speedometer threads
Post by: MilitaryRon on May 23, 2020, 05:08:31 pm
The Smiths Jaeger pattern speedos were a French design and the mounting studs are M6. But this is exactly the same size as 0BA. ( 6mm= .236" x 25.4tpi) .....1/4 bsf (26tpi) will work but gives a wobbly fit.

Ron
Title: Re: Speedometer threads
Post by: ROB KEMP on May 23, 2020, 05:18:47 pm
Did c11 s  have D shaped speedos .I know my c1ol has .
Title: Re: Speedometer threads
Post by: Steve P on May 23, 2020, 05:32:02 pm
Thank you all for replying. As always very helpful.
I think I'll try ordering some 6BA. It looks as though they may fit. The M3.0  and M2.5 screws I have won't fit.
It's fascinating that the Smith's speedo was French and used metric back in the 1950's.

I've looked into what speedo was originally specified for my bike Rob. And it seems that BSA fitted what they had in stock. Or someone in the past 65 years fitted it.

Thanks everyone

Steve
Title: Re: Speedometer threads
Post by: Tman on May 23, 2020, 05:50:19 pm
The Smiths Jaeger pattern speedos were a French design and the mounting studs are M6. But this is exactly the same size as 0BA. ( 6mm= .236" x 25.4tpi) .....1/4 bsf (26tpi) will work but gives a wobbly fit.
Ron

Clearly they're not all the same. I have seen M6 Nylocs holding speedos on, but M6 wouldn't start on these two studs (on a Chrono fitted to a M100 Panther).
That said, and without wishing to start another threads thread, M6 and 0BA aren't interchangeable either as that also gives a wobbly fit.
Title: Re: Speedometer threads
Post by: Steve P on May 23, 2020, 06:04:30 pm
Maybe not BA at all. The M6 nuts did seem to be a very good fit.
Confused!
Title: Re: Speedometer threads
Post by: MilitaryRon on May 23, 2020, 06:06:34 pm
0BA and M6 are exactly the same size and tpi but with slightly different thread angles. Which are a darn sight closer than the 1/4 BSF that are often fitted. M6 are much more readily available but then you have to use a metric spanner >:( Ron
Title: Re: Speedometer threads
Post by: Cosmikdebriis on May 23, 2020, 06:28:28 pm
Gotta love a good thread row. when can we move on to correct spanner sizes ;) ;D
Title: Re: Speedometer threads
Post by: Tman on May 23, 2020, 06:41:28 pm
0BA and M6 are exactly the same size and tpi but with slightly different thread angles. Which are a darn sight closer than the 1/4 BSF that are often fitted. M6 are much more readily available but then you have to use a metric spanner >:( Ron

https://www.pistonheads.com/gassing/topic.asp?h=0&f=23&t=1392008

I reckon we both know that given a lot of wear and piss-poor manufacturing tolerances an M6 nut can screw on an 0BA screw, but with unworn quality parts it's a sloppy DiYer fit at best.
As ever, there's no shortage of the correct fasteners so no excuse for it.
{Incidentally, didn't a pilot get almost sucked out of his plane windscreen some years back when someone on the ground crew thought BA and Metric fixings were interchangeable?}
Title: Re: Speedometer threads
Post by: Steve P on May 23, 2020, 06:59:41 pm
So are we convinced that the speedo threads are BA or some continental metric thread? We British can't be the only ones who liked to invent different thread forms.
I've got to admit to fitting M6 and M8 screws all over the bike. I had lots of stainless steel engineering quality stocks in my garage. The general manager at a company I worked for decided to throw all stocks away as the company was going "lean". It would have been rude not to rescue them.
I'm hanging my head in shame metric fasteners on a BSA
Title: Re: Speedometer threads
Post by: Cosmikdebriis on May 23, 2020, 07:12:03 pm
It's you bike... Do what you like.

Only complaint I would have is if you came to sell it and advertised it as totally original.
Title: Re: Speedometer threads
Post by: Steve P on May 23, 2020, 07:18:38 pm
Not a problem. It won't be original. 12v, indicators and electronic ignition.
Title: Re: Speedometer threads
Post by: Owen on May 23, 2020, 07:22:59 pm
Pre 54 models had round speedo's. C10L, someone C11G's and C12‘s (ohv) had D shaped.  See attached link.
https://bsac10c11c12.co.uk/smf/speedometer/bsa-pre-unit-c-series-speedo-information-180313a/
Title: Re: Speedometer threads
Post by: ianinglis on May 23, 2020, 07:31:36 pm
the thread is M6
these D shaped speedos were built under licence from jaeger (french) and have metric threads NOT 6BA
you will need 3 extra long nuts like these

https://www.ebay.co.uk/itm/ZINC-PLATED-BZP-STUD-CONNECTORS-LONG-BARREL-NUTS-M6-M8-M10-M12-M14-M16-M20/274369167837?hash=item3fe1ad41dd:m:mdmQ535LQZ5pwgdqj-UQ0qw

they are called "studding connectors"


IAN
Title: Re: Speedometer threads
Post by: Steve P on May 23, 2020, 07:35:56 pm
Tremendous. Thanks.
Any ideas about the three case fixing screws
Title: Re: Speedometer threads
Post by: ianinglis on May 23, 2020, 07:41:04 pm
try david and phillip woods

http://www.chronometricspeedos.co.uk/index.html



ian
Title: Re: Speedometer threads
Post by: Steve P on May 23, 2020, 07:43:32 pm
Thanks Ian