E.I.C. A2 magneto for RA Douglas

[cardan]

The EIC A2 magneto for the RA is a bit unusual: it is anti-clockwise rotation (viewed from the drive end) and it mounts with a clamp over the top. A similar version was used on the S1/S2 and OB, albeit with different mounting.

There is a more common version of the A2 that went on 2 3/4 models in the mid 1920s: it is CW rotation, and has a base plate with "wings" and two holes for mounting.

I have built up an A2 for my RA/TW, but I have a couple of issues:

(a) Did the original EIC A2 magnetos for OHV Douglases use the small "M" taper (where the drive gear is held in place by a screw into the armature), or the larger "K" taper? All the A2s I've seen have the small taper, but the magneto drive gear in the RA is bored for a K taper.

(b) What sort of base plate was used when the magneto was clamped to the top of the motor? I have fitted a plain base plate - with no wings - but there is a bit of movement fore-and-aft movement between the mounts. This wouldn't effect the meshing of the gears, but should the magneto fir snugly between the mounts?

Any help appreciated.

Leon

[Hutch]

Leon,

I understand Douglas may have had a special mounting platform for the EIC A2 as used on the OB and possibly other OHV engines for 1924. The distance across the base is 2 15/16". Not sure if this helps but I have sent you a PM with some more details.

Cheers

Ian

[cardan]

Thanks Ian. 2 15/16" (just a tick under 75mm) would be a nice fit between the RA magneto mount lugs, and there is a witness mark on the crankcase to suggest this was the original setup. I found two EIC baseplates, but although both give the correct spindle height, they are both a bit narrow - one by about 1mm the other by about 2mm.

Any idea what the OB baseplate looks like?

Leon

[cardan]

(a) Did the original EIC A2 magnetos for OHV Douglases use the small "M" taper (where the drive gear is held in place by a screw into the armature), or the larger "K" taper? All the A2s I've seen have the small taper, but the magneto drive gear in the RA is bored for a K taper.

I want to get the magneto rewound, but the problem of M (small with BA bolt) or K (large with threaded shaft for nut) taper persists.

The RA book shows a bolt (see below), suggesting the original RA magneto had an M taper. The best magneto I can put together has an M taper. So I'm thinking M taper on the magneto is the way to go.

But the drive gear I have (see below) is machined for a K taper. It has the correct teeth, and the internal tapped thread for the in-situ puller to detach it from the magneto shaft.

If it's not RA, what else could it be off?

Before I modify it to suit the smaller taper, does anyone have a drive gear already machined for the M taper? (The K taper is about 0.500" at the big end, the M is more like 7/16.)

Or did the RA have a weird EIC magneto using a K taper with a clamping bolt rather than the usual shaft and nut?

Thanks

Leon

[cardan]

Or did the RA have a weird EIC magneto using a K taper with a clamping bolt rather than the usual shaft and nut?

I think I can answer my own question: my drive gear has been bored out at some stage to suit a magneto with a larger taper. (The depth of the taper in the gear is only 8mm, as specced for an M taper, whereas a standard K taper is 11mm deep.) So I'd say M taper is correct for the RA magneto. The OB (and probably other models) used a similar drive gear with extractor thread. Of course the thread seems to be something Douglas-ridiculous.

I'll have a go at sleeving my gear, but if anyone has a similar one, but unmolested with a 11-mm-max-diameter taper, lying around unused...

Cheers

Leon