Misc: Ignition Lucas KVF Rebuild - UK Recommendations?
Thanks a lot Tracey for the recommendation, and for the offer of a replacement. I've still got some more bits to do on the bike before it's ready to ride, but thanks a lot anyhow. Very impressed with your detective skills!
It is the front pot with the weak spark, and retarding it to start makes it worse. My spare mag's a manual, I've just assembled it without a cable, so it's on full advance and blanked off the cable hole.
My 60 degree Brough loses the front spark entirely at kickstarting speed if fully retarded, but ticks over quite happily fully retarded on two once it has started.
The best it ever ran was when I got it, the magneto was toast so I modified a magdyno and fitted a HD ATD inside with twin points and coils, it would start just by leaning on the K/S and ticked over like one of those stationary gas engines (interestingly that particular model spins the mag the same way as a Vincent, so you can use a HD ATD and points on a Vincent, they are superbly made compared to any other ATD unit)
Having the internal magneto timing at maximum strength only at full advance is a stupid idea: At poor kickstart speeds you need all voltage you can get from the mag so the internal timing shall be set for retarded position for maximum voltage. Once the engine has started the magneto is run at a lot higher speed , so it will produce healthy sparks anyway . So then the internal timing can be moved away from best position as it no longer matters so much. At least that is what we on the continent did for decades for having an engine capable for kicking it into life from a mag.
That idea with ATD in the drive gear may have its roots in the idea that it will not compromise the internal timing of the mag when the rotor and magnets will keep their timing no matter if advanced or retarded. But I have never come across magnetos on continental machines that got the ATD in the drive gear but instead got nice small ATDs on the breaker end, no troubles from this ever for long times. Just that you set best mag internal timing for max. voltage at full retarded as shown above.
Vic
That idea with ATD in the drive gear may have its roots in the idea that it will not compromise the internal timing of the mag when the rotor and magnets will keep their timing no matter if advanced or retarded. But I have never come across magnetos on continental machines that got the ATD in the drive gear but instead got nice small ATDs on the breaker end, no troubles from this ever for long times. Just that you set best mag internal timing for max. voltage at full retarded as shown above.
Vic
Of course, if you really want manual advance then someone a bit handy with a lathe should be able to modify the flange of a KVF and make the body rotate-able. You would only need 15 degrees or so. The torque through the body of the mag might need something a bit more substantial than a simple advance lever to overcome it. It could also lead to a new and interesting oil leak.
Well there are three ideas
Chris says its the front pot with the poorest voltage If that is so I suppose that means I should use my progressive decompressor lever to select the front pot just over compression rather than the back and accept the shorter throw (99 out of 100 it will be an electric foot anyway)
oexing is in effect saying my lever should move the ring the other way ie time it a 4 btdc and a pull on the lever advances it ...hummm
I think I will miss out Pete,s lathe work at worst I have an ATD I could reluctantly fit and leave the lever for amusement
Chris says its the front pot with the poorest voltage If that is so I suppose that means I should use my progressive decompressor lever to select the front pot just over compression rather than the back and accept the shorter throw (99 out of 100 it will be an electric foot anyway)
oexing is in effect saying my lever should move the ring the other way ie time it a 4 btdc and a pull on the lever advances it ...hummm
I think I will miss out Pete,s lathe work at worst I have an ATD I could reluctantly fit and leave the lever for amusement
Actually my plan would be to modify the internal timing of the magneto so the best spark is at retarded position - IF that is not the case already, which would be stupid.
You want best possible spark at kicking speed, not at high engine speeds as there great sparks are never the problem. To do this you´d have to shift the position breaker plate-to- armature a bit , but I´d think this fault to be not so likely. Just Chris stated above that his mag is weaker at retarded than at more advanced. So there must be some flaw from assembling the mag. After many decades you can never know what may have happened with old iron in the past, so never believe in anything , better check everything.
Vic
You want best possible spark at kicking speed, not at high engine speeds as there great sparks are never the problem. To do this you´d have to shift the position breaker plate-to- armature a bit , but I´d think this fault to be not so likely. Just Chris stated above that his mag is weaker at retarded than at more advanced. So there must be some flaw from assembling the mag. After many decades you can never know what may have happened with old iron in the past, so never believe in anything , better check everything.
Vic
It just requires someone to compare the position of the slots in a cam ring between a manual and auto one to confirm what I say. I will see if I have an auto one later, and also check which cylinder gets the weak spark.
For magneto rebuilds I can thoroughly recommend Tony Cooper. Very old fashioned to deal with and fast turnaround.
Tony Cooper, 110 Olive Lane, Halsowen, West Midlands, B62 8LT. Phone 01215592405
Tony Cooper, 110 Olive Lane, Halsowen, West Midlands, B62 8LT. Phone 01215592405
I have just checked my magneto and all is as I have stated, the best spark is provided to the number 1 pickup, which is the rear as I understand it and the number 2 pickup lags behind that, then of course retarding it drops them both even further back away from the optimal position.