If you're getting 6v at the terminal in the bulb holder with the switch pulled then the wiring up to there should check out... SHOULD.
Multimeters will show a voltage reading when the current is so so very low, so sometimes a dry/broken joint might still show as transmitting power but as soon as you actually load the circuit up (with a bulb or whatever) then sometimes the joint then 'fails' and there's 0v. In many cases a test light is mich better for fault finding (easily made with a bulb holder, some wire and a pair of crocodile clips or similar)

On the other hand I think your issue is probably an earth issue, or the bulb. You said the multimeter was connected to the battery earth. Try the meter across the bulb contact and the base of the lamp unit, or check for continuity between lamp base and battery earth.

Hi Pete

It's a plunger (1953), so has the M-series box (unless I am mistaken) with screw in level plug/clutch adjuster cover.
I have a set of service sheets but any info is always welcome!

I've heard of excess layshaft endfloat or that the 'peak' on the selector fork slot (that the selector shaft pin runs in) is worn.. Anyones guess until inspected I suppose.. I'd better get the fettling irons out of hibernation!! 

Yes those were my initial thoughts, but I called the peg and groove a cam. As you say though pure speculation without stripping it down!

Cheers
Calum

Hi all

I've been out today on the B31, bit of a poor start as the nipple pulled off the clutch cable as I pulled out of the filling station! Left the girlfriend with and ice cream and the bike and rode her Ariel home to solder it back on!
Back on the move again I began to notice my B31 'snatching' in third gear (it has done it on previous rides, so not a new phenomenon!). If I keep the gearchange pedal held whilst releasing the clutch this lessens the likelihood of it happening (good practice anyway?) but doesn't rule it out altogether. It's a plunger model, so has an M series box (I think??) with screw filler/clutch rod cover.
Sometimes letting the clutch out I feel a 'kick' as it pulls into mesh, but it kicks/snatches a bit too sometimes, mainly on the overrun.

My suspicion is the cam that moves the dog clutch for third gear is worn on the 'peak' so not letting the dogs engage fully, and the snatching feeling is the resultant dropping out and back in mesh. Should I be able to see if this is indeed the problem through the cover plate at the rear of the gearbox? Looks a bit tight for clear vision so judicious use of a mirror or endoscope might be needed...

Any pointers gratefully received!

Cheers
Calum

Thinking outside the box slightly... valve lifter definitely clear of the exhaust rocker?

Be very very careful with a bearing without a lipped (flanged) outer race.

Presuming the engine has a bushed timing side earing rather than an SRM type end feed, the lip limits the amount of axial movement. No lip  the movement is not so limited and the crankshaft pinion may even bear against out edge of the main bush and chew it.

When the crank end float is being set it gives just a few thousands clearance between the rollers of the bearing and the outer lip. No outer lip how do you set the float?

Interesting. How is the end float 'set' then? Is there not something to hold the crank in place other than the lipped bearing? Is it just a case of two opposing lipped bearings roughly keeping it in the middle? I've never been in said engine so can't really imagine what's going on.

Calum, when you say the other way round, you mean the correct way, ie coil to the inside (coil to oil)?

Indeed. Good habit, even though as said above by lightning&starfire in this application it doesn't matter too much

Classic brake services in Chapel en le Frith Derbyshire do this. I plan to use them to rebuild my wheels. I have had one recommendation for them but not used them yet.

Seem hard to find on google and number is tel:07811356619

Let me know how you get on.

Chapel is the home of Ferodo brake and I would imagine this business has been spawned from them.

John

That's the people I am thinking of. I believe they (or Ferodo) will make linings to any size/shape as well.