The BSA A7-A10 Forum

Technical => Lucas, Electrical, Ignition => Topic started by: Greybeard on 28.03. 2016 11:39

Title: Rear lamp screws?
Post by: Greybeard on 28.03. 2016 11:39
One of the long screws from the rear lamp lens on my bike has gone AWOL. The lamp is a modern pattern replacement for the Lucas L564 unit so I expected a metric thread but after holding the other screw up to my metric taps I think the thread is probably BA. The place near here that used to do nuts and bolts where I could have shown them the other screw as a pattern has closed. I could order online but I'm not absolutely sure about the thread pattern and size. Can you confirm that these modern rear lights are still using BA threads; also what gauge? Thanks.
Title: Re: Rear lamp screws?
Post by: Beezageezauk on 28.03. 2016 12:18
Hi Graybeard,

I believe that electrical apparatus still use BA threads.  If so, it might be an idea to take your remaining screw to an electrical supply shop where you could try BA nuts on the thread.  They might even be able to replacement the missing screw (and a spare to carry about with you)!!  Long shot maybe but could be worth a try.

Beezageezauk.
Title: Re: Rear lamp screws?
Post by: duTch on 28.03. 2016 12:20

 B-Macc rounded me up, but I shall press on

GB, if you mean the screws that hold the actual lens, Can't say for sure, but as a stop-gap, I think I used WW ones from the boat shop. Can't recall the size just now, but must be 7/32,3/16 or 5/32 (which I think is fairly close to BA); but that's in a probably original type base 
  (#575219)    *????*
Quote
http://draganfly.co.uk/index.php/accessories-a-misc/product/11332-
*????*

 Something I've done to save losing screws is put a suitable size 'O' ring on the inside, so if it comes loose doesn't jump ship, Good for inside dynamo covers too, but haven't done that yet  *dunno2*
Title: Re: Rear lamp screws?
Post by: Greybeard on 28.03. 2016 12:38
...it might be an idea to take your remaining screw to an electrical supply shop...
Hi Beezageezauk, don't see you on here often lately. Thanks for the tip.
Title: Re: Rear lamp screws?
Post by: Greybeard on 28.03. 2016 12:39
Something I've done to save losing screws is put a suitable size 'O' ring on the inside, so if it comes loose doesn't jump ship
A very good idea!
Title: Re: Rear lamp screws?
Post by: Greybeard on 28.03. 2016 13:35
...WW ones from the boat shop...
No boat shops near here!

Actually, it often sounds like you guys in the Antipodes are served well for bits and bobs. In the UK we only seem to have DIY supermarket outlets, (HomeBase, B&Q etc.) with fairly minimal choice! Maybe you guys are far more likely to do stuff yourself.; it looks like we are rapidly heading towards a consumer culture here.  *sad*
Title: Re: Rear lamp screws?
Post by: bsa-bill on 28.03. 2016 14:57
Quote
heading towards a consumer culture

Think we arrived there a decade or two ago GB  *sad*
Title: Re: Rear lamp screws?
Post by: RichardL on 28.03. 2016 17:26
GB,

Seems they are 4mm, 0.7 pitch and right around 45mm long. (I'm giving these as metric dimensions despite the fact the world must return to imperial.)  You can see in the picture that the major diameter is 3.84mm, which falls in the range for a 4mm screw.

Richard L.
Title: Re: Rear lamp screws?
Post by: Greybeard on 28.03. 2016 18:19
Seems they are 4mm, 0.7 pitch and right around 45mm long. (I'm giving these as metric dimensions despite the fact the world must return to imperial.)  You can see in the picture that the major diameter is 3.84mm, which falls in the range for a 4mm screw.
Richard, many thanks for your input. I agree with those dimensions but the thread pattern is not 4mm, it's courser than that. Using the thread gauge in my tap & die set the thread count is close in pitch but not thread depth to the 0.8 blade, (whatever that means). I found a 4BA tap in my toolbox which is close in diameter but the 4BA thread is finer than this screw. Any more ideas chaps?
Title: Re: Rear lamp screws?
Post by: chaterlea25 on 28.03. 2016 18:46
Hi GB,
Its probably "Chinese" whiitworth metric *razz*
Some stuff comes from China with metric diamater and whit thread numbers  *eek* *eek* *eek* *eek*
Screw in the 4mm tap and use a metric screw

BTY I now see "New " Lucas (repro) lamps on th market since the big W bought the lucas name *razz*

On the original Lucas the threaded piece is fixed to the base and slot headed sleeve nuts hold the lens
I found a new genuine Lucas lens for my SR and made the sleeve nuts from SS to fit onto M4 screws fixed to a replica  base

I won't tell you how much I paid for the geneuine light unit for the RGS project  *dribble* *dribble*

John
Title: Re: Rear lamp screws?
Post by: morris on 28.03. 2016 20:51
To add to the confusion, I have a repro Lucas rear light on which the lens screws are definitely 3/16 ww 24 tpi.
You may be able to find them at a classic car parts dealer. That's where I get my ww from. A lot of early 50's cars contained a surprising amount of ww (and also BA for electrics)
Title: Re: Rear lamp screws?
Post by: duTch on 28.03. 2016 23:59

 GB, As you say yours is an aftermarket unit, but to satisfy my curiousity, I pulled a screw out of mine, and M.d. measures 0.1845" (4.70mm) which according to the chart I use, the 2BA dia is 4.699mm.
 The thread is not 2BA though, and I can't find my gauges, but it has the same pitch as what I guess is a spare 3/16" WW screw (3/16 = 0.1875").

 I remember being surprised that they screwed in easily, but it may have been due to a previous owner improvising (I've had the backing unit since the early '80's but never used it until this rebuild four years ago).

  The screws that hold the unit to the mudguard piece are finer and similar dia., so I'll assume 2BA until verified.
 
 Hope that's a bit helpful (The reason I buy them from the boat shop is they are stainless, I can choose, and boatie is open saturday arvo *smile*)

Title: Re: Rear lamp screws?
Post by: muskrat on 29.03. 2016 00:45
Just measured my non genuine. M4x0.75 45 long.
Cheers
Title: Re: Rear lamp screws?
Post by: RichardL on 29.03. 2016 02:42
 The metric chart I looked at connected .7 pitch with 4mm, but I counted just under 10 threads for 7mm, so .75 sounds right to me.

Richard L.

Title: Re: Rear lamp screws?
Post by: muskrat on 29.03. 2016 03:38
Bugga, I do need new goggles. Your right Richard M4x0.7.
My apologies.
Cheers