Magneto - Quick Bench Check

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Mick D
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Joined: Mon Mar 24, 2014 5:44 pm
Location: Aberdeenshire

Magneto - Quick Bench Check

Post by Mick D »

Hi

I am refurbishing a K2F magneto and would like to confirm it's function before refitting to the bike. The theory suggests that if I fit the HT leads and plugs, grounding the plugs to the mag body, the mag should produce sparks when rotated.

Should I expect to see sparks just turning it by hand or will I need to spin it faster or for a longer duration?

Oh! and am I leaving myself liable to become a ground and subject to electrical stimulation :o :o

Regards Mick
SPRIDDLER
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Re: Magneto - Quick Bench Check

Post by SPRIDDLER »

I've managed to get a spark on a refurbed mag by just finger twiddling it over the max flux 'flip' point. No electrical shock.
'There is a tide in the affairs of men
Which taken at the flood............'
g80csp11
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Re: Magneto - Quick Bench Check

Post by g80csp11 »

Agree with Nev, a good mag will jump 1/4" easily by hand , bright blue spark
my refurbished mag still does that after 10 years while waiting for me to do the rest of the bike
cbranni
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Re: Magneto - Quick Bench Check

Post by cbranni »

Agree with the comments above "a flick of the wrist" should be enough to generate a good spark, Groily will confirm in due course.

Colin
only dead fish go with the flow
Dixter
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Re: Magneto - Quick Bench Check

Post by Dixter »

Lucas's standard for this magneto is to jump a 5.5 mm gap, full advance, turning 150 RPM, with under 5% miss. This is best replicated with a motor driving the input shaft, but easily tested with a dozen turn of string around the shaft, and a slow steady pull.

Ciao, DC
Dick Casey
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Groily
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Re: Magneto - Quick Bench Check

Post by Groily »

Yup, and a good one might do rather better. 100% sparks at 130-140 is what I always aimed for, and sometimes have seen 100% at 110rpm using three point 5,5mm test gaps per Lucas. Advanced, and at room temperature that is. At a test temp of c 50°C, it will drop off a bit, but if it won't perform hot under about 180rpm without missing, fully advanced, I'm not happy. Retard will add a good 30-50rpm to the figures, depending on exact amount of movement on the camring, and the quality of the spark will reduce a bit too. The later steel contact breakers will often be marginally better at very low rpm - although I personally far prefer the brass type.
A flick of the wrist should be good . . . as long as it's turned the right way, which is anti-clock on any K2F on our bikes.
If there is any way of testing the interval between the 2 sparks, it's a good plan . . . can be done with a strobe on the bike of course. But worth doing because K2Fs are the world's worst for not delivering at 180:180°. Errors of 3, 4 or even 5+ degrees at the mag are not rare - and that has to be doubled up as the mag goes half speed. Six, 8 or even 10+ degrees of timing error between cylinders ain't good . . . .
Mick D
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Joined: Mon Mar 24, 2014 5:44 pm
Location: Aberdeenshire

Re: Magneto - Quick Bench Check

Post by Mick D »

Thanks Guys

Always nice to know what to expect :beer: This is my first magneto bike so a bit of a learning curve, very pleased with fat blue sparks at very little rotational speed :D

Regards Mick
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