Brightspark Magnetos

Reconfiguring the K1F, K2F & KVF

Special tools/materials required

• Soldering iron (50W preferably) and solder

• Adhesive-lined heat-shrink sleeving, and a heat gun or other suitable heat source for shrinking the sleeving

• Possibly a small solder tag

Procedure - overview

Having eased the drive-end end-piece away from the bobbin, you will be able to see whether the armature is fitted with an original Lucas condenser (picture top right) or with a more modern device which is usually potted in resin. The procedures to be adopted are roughly similar for both and summarised by the following schematics.

On the right is a thumbnail of a 'before-and-after' schematic applicable if fitted with original Lucas condenser. Click on the picture to see a clearer printable Acrobat file.

On the left is a thumbnail of a 'before-and-after' schematic applicable if fitted with more modern condenser potted in resin. Again, click on the picture to see a clearer printable Acrobat file.

Procedure - detail

With the armature held in a vice as in the picture to the right, i.e. with the HT spike nearest you, you should see a wire in a sheath coming out of the left-hand side of the lower end of the bobbin. This is the common earth of the HT and LT windings.

You may be able to see where it is connected to earth, for example by being soldered to the metal casing  of an original Lucas condenser or its metal mounting bracket, or to a solder tag connected to the brass end-piece. If so, unsolder it. A decent soldering iron, say 50W, is needed to get the joints to part. Try to concentrate the heat on the joint. Steady hands are needed, as the coil and the wires leading from it won't respond well to excess heat. Once the solder is molten, you may need to wiggle to wire with a pair of long-nosed pliers in order to free it. But be careful not to break the earth wire near its exit point from the bobbin. If you do break it there, the bobbin will need to be rewound.

If a replacement condenser has previously been fitted, it may be potted in resin, and an earth terminal post may be sticking out of the resin with the earth wire of the bobbin soldered to it, as in the picture to the left. In this case, unsolder the earth wire from the post.

Alternatively, the earth wire may disappear into the resin. If you can carefully excavate into the resin with a fine chisel or punch to reach the place where the wire is soldered, so much the better, and then unsolder it. As a last resort, you may need to snip the wire, using a pair of fine side-cutters, but snip it as far away from the bobbin as possible to leave the maximum amount of wire attached to the bobbin.

With the armature rotated 180 degrees from its previous position as shown in the picture to the right, i.e. with the HT spike away from you, you should see a  sheath coming out of the left-hand side of the lower end of the bobbin. This sheath should contain two wires. One is the live end of the LT winding. The other is the link wire up to the nut for the CB centre screw at the other end of the armature. These two wires should be connected to one side of the existing condenser. You need to disconnect them, preferably by unsoldering but if necessary by snipping as far away from the bobbin as possible, in the manner described in the previous section.

Having disconnected the wires, you can now separate the drive-end end-piece completely from the remainder of the armature.

In the example in the pictures, there are two capacitors in parallel in the end-piece, potted in resin. They need extracting. As they aren't going to be used again, some chiselling is quite in order  . . . a fine-pointed chisel and light hammer gets the chips flying and starts to unearth the capacitors.

Clean up the end-piece. You should have found one, and possibly two, short 5BA screws in there, screwed into the smaller holes adjacent the 2BA holes for the long through-screws. Retain it/them.

Place the bobbin in the vice (with soft jaws) in the position shown in the picture, i.e. with the HT spike at the bottom rear.

The pair of wires at the top left 10 o'clock (LT live wire and LT link wire) need to be electrically connected to each other but insulated from everything else.

It may be that they are already nicely twisted together and soldered together. In that case, merely neaten up the end and then sheath them in two layers of adhesive-lined heat-shrink sleeving.

You may, however, need to (a) trim back some of the original sheath, (b) bare the wires of their insulating coating or old solder, (c) twist them together, (d) trim them and (e) solder them together, prior to sheathing them in two layers of adhesive-lined heat-shrink sleeving.

(In some of the pictures, the brass end-piece at the CB end of the armature has been removed. However, there is no need to do that.)

With the bobbin still in the vice in the same position, the single wire at bottom right 4 o'clock is the earth wire and needs to be re-attached to the brass end-piece using a solder tag and the 5BA screw. That needs to be done before the brass end-piece is reattached to the bobbin. You therefore need to decide whether the wire is long enough as is, or whether it needs an extension piece adding. If so, a single strand of copper wire of about 0.5 mm diameter is suitable.

So, clean the end of the existing wire. If an extension piece is to be used, twist it with and solder it to the existing wire. Then solder a 5BA, M3.5 or M4 solder tag to the end.  Then sheath in two layers of adhesive-lined heat-shrink sleeving.

Now, using the scribe marks you made earlier, work out which of the two 5BA holes in the brass end-piece is going to have the earth wire connected to it, and block the other hole with a spare 5BA screw, silicone or other suitable material. This will prevent any grease from the drive-end bearing getting into the interior of the armature through the hole.

Now attach the earth wire's solder tag to the remaining 5BA hole in the brass end-piece, taking care not to stress the wire too much, and then reassemble the drive-end end-piece with the bobbin, and refit the two long through-screws. Tighten them fully and then release them slightly.

You can now measure the LT and HT resistances again and check whether they are unchanged from the figures you obtained earlier. Make a note of the HT resistance.

Next: Reassembling armature