WD B40G timing cover screw threads

[Denaro]

Hello,

I'm struggling to find the correct thread for some of the timing side cover screws on my 1967 MK1 WDB40G.
There are three smaller holes at the front of the casing and the allen screw sets I've bought have 2BA screws (I think) for these positions which don't fit.
The rest of the screws (BSCy I think) are fine.

Any advice for the correct thread gratefully received.

Thanks

[Spaceman]

They are supposed to be 2 BA x 5/8" screws according to the parts book - the same as a standard B40. Just checked my B40WD and that's exactly what is fitted.

Is the problem that the tapped holes are the right diameter but the 2 BA screws don't screw in, or is the problem that the diameter is wrong? Do you have one of the original screws or were they missing when you got the bike?

[Denaro]

Spaceman, thanks for your response.

The tapped holes are the right diameter but the 2BA screws don't screw in.
They go in 1 or 2 turns then get too tight to turn.

I dont have the original screws. The bike has been in boxes for 40 years.

The parts book I have doesn't state the screw size. What parts book are you using ?

[Spaceman]

They are the same 3 x 2 Ba x 5/8 screws in all the BSA unit singles from the C15 right up to the last B50!  The B40WD parts book shows the same 3 x screws.

I can only assume someone has used non-BA screws in the past which have re-cut the threads. However, most of the alternatives (BSF, UNF and metric fine) are all about 32 tpi and close enough to 2 BA with 31.3 tpi. 3/16 BSW might have been used which has only 24 tpi. If you can get hold of a 3/16 BSW screw, it might be worth seeing whether it will fit.

[Spaceman]

If it was me and a 3/16 BSW screw didn't fit, I would run a 2 BA tap down the holes and then check whether the resulting threads were strong enough to take the required torque. If not, you can get 2 BA Helicoils to restore the threads.

You have to bear in mind that this started life as a military bike and it would not surprise me if an army mechanic swapped screw threads possibly because they considered a 3/16 BSW thread more durable than a 2 BA thread, especially into a soft aluminium inner timing cover? That said, my B40WD still has the 2 BA threads!

[Spaceman]

I've just had a look at a spare inner timing cover I have and found it was difficult to screw in one of the 2 BA screws. The problem was that this particular tapped hole has a lot of gasket cement inside it stopping the screw from turning easily - the small diameter probably makes it a bit more prone to this problem than the other larger outer timing cover screws. Running a 2 BA tap through it sorted the problem. Ideally you need to use a bottoming tap with these blind holes.

[Alan]

Has the supplier sent M5 screws.

[Denaro]

3/16 BSW doesn't fit.
I'll try cleaning out the holes and easing in the 2 BA screws. Failing that I'll try the 2BA tap.

[Spaceman]

If you don't have a 2 BA tap but you do have a spare 2 BA screw, if you cut a 1/4" long slot in the end of the screw, you can then use it to clean the thread - the slot provides space for the debris to accumulate. Tried it on my spare cover earlier and it worked a treat!

[Denaro]

Your slot idea worked ! I now have a full set of nicely fitting allen screws for the cover.

Thanks a lot for your help!

[Spaceman]

Glad to help.

Always interested in any B40WD restoration - if this one has been in boxes for 40 years, does that mean it left the army in that form?

[Denaro]

Not quite. It's been in the back of a garage all that time and it's a long way from it's former olive-green splendour.