Reply To: Oxford Allen Scythe Villiers Mk25c

[sidevalve5]

Andy, fully concur, if all the components in a magneto coil, points, condenser set up are good. Then so is the spark. Angus Shapland concluded that a Meco transistorized unit was not superior to a good points system. He liked them because it got rid of the condenser and after he had serviced a machine with points for a customer. It was then laid up for a while in damp conditions and when brought out again, would not start. The customer moaned, but he found all that was wrong was corrosion on the points. The Meco unit eliminated that problem, it was ‘fit and forget’. Have a Gravely L with a Bosch mag, a Trusty with a Jap 6 with a Wipac CJ mag and a Hayter Condor with a Kohler K181 with a flywheel mag. To all three, after a light hone of the points and resetting achieved a spark at 6mm. Left the original condensers in place and they all started easily and tickover is smooth. As an experiment I replaced the condenser on both the Gravely and the Kohler with a polyester film capacitors, there was no improvement. But I also have engines that could not attain a spark at 6mm, but would at 4mm. The coil tested fine, the points were clean and set up correctly. Starting was difficult and tickover erratic. This was especially a problem with manoeuvring a Trusty in tight spaces. The mags were Wico Series A’s, spark was 4mm, one had a condensor that failed a megger 500v test of a 200M ohms requirement, the other passed it. Fitted capacitors and both mags sparked at a 6mm gap. The improvement in the overall machine’s performance was remarkable. Have had transistorized ignition modules on engines that are difficult to start. The spark gap was 4mm or less, even though the coil passed a manufacturer resistance test. I replaced the module with cheap non-OEM ones and the spark exceeded 6mm, the engine was fixed. But I digress (hugely).

Back to David’s flywheel and I have another idea. If the hub HAS to come off, try using a 4” thin blade on a disc cutter with a longitudinal cut. From the replacement flywheel calculate the depth of cut that would be just touching the crank at any given point on the hub. Where the radius of the disc limits the cut near the armature plate, drill 1/8” holes at ¼” centres, then enlarge them with a ¼” bit. With feeler gauges measure the gap in the cut, put some steel wedges (chisels or screwdrivers) in the cut and tap tight. Measure the cut gap again to see if its parting. Try to remove the hub with a puller, if this initially fails, apply some heat to the hub. Still no go, do a similar cut on the opposite side of the hub. If that still fails, go down the pub to drown your sorrows and curse the time you ever contemplated messing around with a knackered old piece of machinery. If its any consolation, I’ve been there many times.

Grahame