Reply To: Oxford Allen Scythe Villiers Mk25c

[sidevalve5]

Hi Dave,

Personally I would do the easy and/or cheap options first. If the multimeter tests are within the range indicated and the points are clean and correctly adjusted. But there is still no, or just a very weak spark. Suspect the condenser and as you say, you can fit one externally. Only fit new, not second hand or NOS. Would enquire at Villersparts if their square type is a modern capacitor and if so get one, or one from Brightsparks, or a 630v 220nF / 0.22uF capacitor locally. If the coil appears OK, but access to the points is so poor you cannot do the degree of work required to get them in good condition. Would fit an externally mounted Meco or Nova ignition unit. Angus Shapland (aka wristpin) has fitted lots on Villiers Mk25c’s and speaks highly of them. It appears the only problem with them is the voltage induced by the flux reversal has to be high enough to trigger the module. It is suggested 3v is needed, so the flywheel needs a bit of a spin. If the primary coil is poor, or there is a short in the circuit, then this may not be enough.

If the coil is duff, then things get a lot more difficult. You could as you say, make up a total loss Kettering ignition system and leave the points in place. However, I would firstly check the timing which should be 5/32” BTDC. If someone was so hamfisted as to overtighten the captive nut, I would not trust them to get the timing correct either. Would be great if you could get the screws undo that hold the brass flywheel onto the hub. But if you could do that, I am presuming you could access the coil and points sufficiently to remove them if required. Then am not sure if fitting the flywheel you have got from ebay will be of any benefit. Other than because you have damaged beyond repair the original when you removed it. If you are still going for the total loss ignition system, then if the magnet is in the incorrect position on the flywheel, it will make no difference. Would be surprised if the magnet was not aligned with the points cam lobe anyway. When the magnet passes over the soft core of the coil and flux reversal occurs, the voltage to the primary jumps. It is at that instant the points open, current ceases to flow through the primary (a good condenser is needed), the resulting collapse of the magnetic field induces very high voltage in the secondary which seeks a route to ground. So the lobe on the flywheel has to be synchronized to the position of the magnet on the rim. As the Mk25c does not have a keyway, you can adjust the timing. A problem that could occur in swapping the flywheels of different models could be the difference in magnet length and cam lobe profile.

If import duties and carriage from the UK are prohibitive. You could always try the single wire energy transfer system I posted on the 9th February. You will still need the 6v motorcycle coil for the Kettering system. The only extra would be 100g of 22swg enamelled wire and the time it would take to strip and then rewind the coil. For the total loss system you will need a battery and the time it takes to make a mounting for it. The coil, wire or battery could all be sourced in France. Am thinking of making a bit of test equipment with the battery I use in a cordless drill and fitting a potentiometer to regulate the voltage.

Lots of choices, but think you have settled on a course of action. Wish you the best of luck and keep us posted to how you get on.

Grahame