Headlight bulb spec for '48 Triumph Speed Twin?

[sprangerny]

Redoing some wiring and my headlight bulb was frozen in the socket. Took some work to get it out - but now can't read the part number/code above 'BRITISH'. DOES ANYBODYI KNOW WHAT THIS PART NUMBER MIGHT BE? MANY THANKS.

[AFJ]

For 1946-48 Triumph Speed Twin the standard headlight was a Lucas MU42/F700P 7" (Pre-focus type)
Main bulb was a # 312, pilot bulb a # 988.
The # 312 bulb was a 6 volt, 24 watt lower, 30 watt high beam double filament, vertical dip type.
Sounds like the standard bulb available from dealers like Walridge Motors or British Cycle Supply.
AFJ

[sprangerny]

1. Would like to check and make certain that this 'carrier-feature' is the standard fitment for the Lucas MU42/F7700P 7" headlamp you've mentioned. Just checking.
2. The base diameter (small) of the removable Main Bulb (and the Pilot bulb) measures .587 (or 15mm)
3. My original, dog-eared manual states the Main Bulb is a Lucas No. 70; and the Pilot is a Lucas No. 200.(any mfg cross-reference tables available?)

Can you take a look at the attached photos and see if I'm on the right track in sourcing bulbs? Or was there a substitution in hardware back in the bike's early history.

Thanks guys HeadlightAssy.jpg

[Rubone]

Bases and pin locations are standard internationally. Triumph used that Lucas light for years with minor variations including all the Trophy models.

[AFJ]

1. Would like to check and make certain that this 'carrier-feature' is the standard fitment for the Lucas MU42/F7700P 7" headlamp you've mentioned. Just checking.
2. The base diameter (small) of the removable Main Bulb (and the Pilot bulb) measures .587 (or 15mm)
3. My original, dog-eared manual states the Main Bulb is a Lucas No. 70; and the Pilot is a Lucas No. 200.(any mfg cross-reference tables available?)

Can you take a look at the attached photos and see if I'm on the right track in sourcing bulbs? Or was there a substitution in hardware back in the bike's early history.

Thanks guys HeadlightAssy.jpg

After some further search of the Lucas catalogue, I have to revise the information on the bulb needed. The bulb holder (Lucas called it a "backshell") (part # 515191) takes a 168 (24/24 watt) or 169 (30/30 watt)headlamp bulb, original headlight bulb was a #170 bulb. The pilot is a #200.
Don't know offhand of a source.
AFJ

[sprangerny]

Many thanks for the info. Am still hunting around Stateside for anyone that has a 2-lower-pin, miniature-base bulb, 2 element, with either 24/24 or 30/30 watt output. Am using an 1158 in the meantime, just while I'm rewiring, etc. Will go to Negative Ground (and guess flash the dynamo?), as it's otherwise very confusing!

[AFJ]

British motorcycles from 1951 and earlier were generally negative ground. 1952 was when they turned to positive ground. As to a miniature base bulb like a 170, i would look on the web for vintage obsolete bulbs for cars as there are some small base ones being made with LED bulbs.
Curiously I looked in my shop storage and found a pre-WW2 headlight that had come with a dismantled '38 bike in 1969. I ran the rebuilt bike with this pre-war headlight for a few years and it was a terrible headlight as far as lighting up anything. I found a new kit aftermarket (1950's) that converted an 8" Lucas (pre-ww2) headlight to take the postwar Lucas7" headlamp and #312 bulb and it made a world of difference. Not QI but at least you could see something. The old headlamp used the 170 bulb and from the filament you can see why it was such a poor light on either high or low beam.

[sprangerny]

Thanks for that background. Glad I'm not the only one with lighting/switch/bulb questions and issues. Have a variety of parts coming, so will experiment with different options to see if I can get a 6 volt system to produce at least a minimum of lighting (without resorting to LED's).

[sprangerny]

Had myi1948 3T judged last week at an AMCA National. The judges weren't sure if my blade-style, plug wire connections were correct. And the little clip holding the plug wires from flapping in the wind. So they just docked it 1/4 point. 3T-PlugTerminal&Wires.jpg Any thoughts?

[AFJ]

Well, from the book "It's A Trumph" by Ivor Davies published by Haynes/Foulis, 1980 pages 95, 96 and 97 show the spark plug leads with the small clip low down and a bigger clip higher up which has a small flange and bolts to the right side mounting bolt of the carb to the intake manifold. The paired wires go vertically up, close to the right side of the carb, up under the tank and over the center top of the intake valve covers and when the paired leads are just ahead of the intake valve covers the leads split and go to the spark plugs. The plug caps are the black bakelite fully covering the plug insulator type. The plug lead to the right side plug goes under the oil line to the valve gear. A very neat arrangement,
Never been an AMCA judge under the current system, or ever had a bike judged under the AMCA system although an AMCA member for 44 years so couldn't say if 1/4 point was appropriate or not.
Al Johnson, Georgetown, Ont., Canada

[sprangerny]

Interesting. Will have to try to find that photograph. Is it possible for you to include that photo in one of these Forum Messages?

[Rubone]

I have that book and can scan it if needed. DCP_4202.JPG

[sprangerny]

Wow! That's quite the British book collection! Or just take a snapshot, and upload that image? Either way would be GREAT!

[sprangerny]

There were SO FEW 1948 3T's shipped over the North America (not sure how manky), that most guys have never seen one.

[Rubone]

Here is a picture from Steve Wilson's "British Motor Cycles" Volume 6.

3T plug wires.jpg