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DU42 headlamp size

Hello everybody,

It's been quite a long time since my last post. I've been reading the forum now and then, but seems that taking care of a child doesn't leave you much time to spend on classic bikes.

Just to update my BSA's info, I had it running for some time, but on sept 2018 my M20's clutch failed, and the bike needed an overhaul (gearbox, magdyno, front suspension, rear wheel... the only ok were the carb&engine). After spending an entire year in hands of a supposed "old bikes restorer", I finally found a professional mechanic who has fixed everything. I sent him the bike (his worksop is 1200km from home, but it was really worth it!), and he got everything working in less than a month. I have nothing but good words about him.

The next thing that I must work on now is the headlight. The bike came with an original DU42 marked headlight, but it was fitted with a different reflector, glass and rim. I bought the rim, reflector and glass from , for a 6" headlight, but there is no way to make them fit in my headlight shell.

Before buying the parts, I checked the technical section and foud: "LUCAS 6" Size Panel Headlight TYPE DU 42, used on BSA WD M20 from early-1942." So I assumed that my shell was 6", but on ebay and other pages I find DU42 listed as 6" and also 6 1/2".

Were there 6 1/2" DU42's? Or maybe my shell is so beaten up that the correct rim won't fit?

Thank you for your help,

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Re: DU42 headlamp size

You bought a replica rim ?
There might be some risk in that when it comes to fitting.
Maybe buy a head lamp shell there as well ?
As far as I know the headlamp is 6.5"

Re: DU42 headlamp size

We seem to refer to the headlamps as 6" and 8" when in fact that is not the exact sizes. It's just to ID the different lamps. Ron

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Re: DU42 headlamp size

Hi All headlamps measure different to what they are called something to do with circles and metal if you measure your wheel rim it will be stamped 19 inch but it doesn't measure 19inch with a tape measure i could have sold many a headlamp at the jumbles until someone gets his tape out

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Re: DU42 headlamp size

DU42/C is a 7” mid thirties era
They are easily identified by the fact that the mounting bolts are part of the shell, rather than screwing into it.

Re: DU42 headlamp size


Ok, so 6in and 6 1/2in may be referring to the same size. Thanks for the info.

I have reached the seller and may try to buy the shell there. It is just that I wanted to use the original shell.

Mine doesn't have the bolts welded, so i figure it is not the du42/C.

Thank you all for the knowledge!

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