Hello, Wondering if anybody has successfully used a smaller Villiers coil (such as those available on online auction sites (£23)) as a replacement for the larger types (2 1/2" long). The gap could be bridged by using some copper pipe or other suitable metal. I have tried this but as yet have not had success. This may be due to other component failure (condenser/points) so my experiment is still ongoing. I have 2 mowers in need of the larger and considerably more expensive coils. Any information or ideas appreciated.
Not sure of the answer but unless the other components are good you don't stand a chance of finding out.. My uninformed guess is that for a chance of it working the soft iron core of the "small" coil would need to be extended into the pole pieces - not really a practical proposition . Not only that, but the electrical characteristics of the correct coil will be matched to the magnetic characteristics of the flywheel - the "small" coil won't be.
Condensers can be tested or renewed for modest money . Points are cheap and even quite pitted ones can be recovered by careful work with a small carborundum slip stone.
Interesting question about bridging the gap. The requirement is to complete the magnetic circuit of the "horseshoe" and I suspect that you would need to use similar metal to that found in the coil piece, usually soft iron. Whatever you use must be of ferrous composition for its magnetic properties. Copper doesn't qualify here, nor does aluminium.
The main problem, as I see it, is that the magnetic circuit will be further interrupted at the point where the two pieces meet. That additional joint may provide too much magnetic "resistance" to drive sufficient current into the primary of the (possibly) smaller coil. Experimentation is required.
However, as you mention, the other components (magnets, condenser, points and wiring) need to be in good shape to have a chance of it working.
Thank you for all the advice. I had used aluminium as my metal choice as I had some well fitting tube available and was thinking on the lines that it only needed to conduct electricity for it to work. I had not considered that it would need to be magnetic, but now of course it makes sense, so there is still hope. I shall now substitute the aluminium for a ferrous metal and see what happens. I had replaced the condenser for a new part. My other doubts were if I had not insulated the points apparatus properly.
Soft iron is used in these things because it doesn't retain magnetism for long, and thus allows the magnetic field to collapse quickly and create a voltage in the coil's primary winding.
Let us know how you go with your experimenting.
I have just heard from another forum reader that he has successfully extended a short coil to replace a longer one using mild steel extensions spring loaded to keep them in place and has been running his Villiers engined Qualcast 16 all summer without issue.
These are his images
While soft iron (such as in coat hangers) is perfect, mild steel is next best.
It's not clear to me from the photo how he has attached those springs. Are the steel pieces hollowed out?
My understanding is that they are hollowed out to act like spring loaded pistons but my only involvement has been to post the images on behalf of the forum contributor who, for whatever reason, was unable to do so.