Author Topic: Magneto say Fuel - Spark = Bitch won't start ? Renamed  (Read 1883 times)

Offline Topdad

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Re: Magneto say Fuel - Spark = Bitch won't start ? Renamed
« Reply #45 on: 15.06. 2017 15:42 »
duTch, glad you got it sorted ,with all that lot changed it's got to be good for a good few yrs now !!
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Offline duTch

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Re: Magneto say Fuel - Spark = Bitch won't start ? Renamed
« Reply #46 on: 15.06. 2017 22:42 »

 Firstly I forgot to thanks all for their input and forcing me out of the two-week denial that it could be a Maggy problem- last time I was in denial for ten years *bash* *bash*

 yo Bob, I'm not sure if it's best it outlives me or I outlive it  *smile*

 Julian, I can't find any number on mine, but I did find a couple of hairline cracks starting...my only thought on the longer bass segment is maybe longer spark duration if that's possible- think I'll leave that up to the Gurus

 Yes Richard, does look a lot, but I guess it's now fluffed up a bit...I did the hole a while ago and forgot to mention it seems fairly good so far, but will talk about that elsewhere, as with the 'back scratcher'....I started using them a while ago for a host of different things.... *smile*
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Have a '74 850T Moto Guzzi since '92-best thing I ever bought doesn't need a kickstart 'cos it bump starts sooooooooo(mostly) easy
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Online groily

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Re: Magneto say Fuel - Spark = Bitch won't start ? Renamed
« Reply #47 on: 15.06. 2017 23:37 »
Ref JulianS' query on sliprings  . . . it's true there were some modest variations in the length of the brass strips on different rings. Quite why I don't know for sure, but the single critical thing is that an HT brush - one only! - must be fully on the brass at the firing point for that cylinder.

With manual advance and retard, the brush will be on a different spot on the ring according to the position of the camring (the position of which relative to the armature controls the exact moment at which the contact breaker opens). That variable may explain the use of slightly longer segments on some models, especially if using more advance and retard than is typically found on a standard K2F (which is around 18-20° on the mag via a notch c. 11mm wide limiting the camring's movement).

As long as one HT brush is in full contact with the  brass segment at all positions of a manual camring (set correctly in its housing) when the points open, and as long as there is no possibility of the spark's trying to hop across to the other brush at the same time (owing to an overlong brass segment connecting both brushes, or nearly doing so), all will be well.

The sliprings made by the best UK supplier for both clockwise and anti-clockwise rotation twins use a strip of about 90° or a bit more maybe of the circumference, handed accordingly. This is adequate for correct operation of any manual K series mag I have seen, and also works perfectly OK on 50° V twins with an ATD. Haven't had the opportunity to see if there's enough brass on them to work in all circs on a pre-ATD V twin, like an HRD, but suspect there is probably just enough provided there isn't too much movement available on the camring or that the movement is slightly restricted to avoid under- or over-shooting the brass at the firing points.

The 35Kv marking refers to the dielectric strength of the material - ie its resistance to leakage at high voltage.

While it is common to see 25° or even 30° sometimes of advance/retard on single cylinder mags (which in most cases have a continuous brass strip through 360°), there isn't any real need for it I don't think except possibly for trials riders, and no Lucas twin I have seen has that much.

So the modern replacements available can be reckoned to work on all the models we're likely to encounter, with the possible caveat concerning manual advance V twin engines, and their resistance to leakage is as good as we'll ever need. Testing them at elevated temperatures linked in series with ignition coils operating at considerably higher voltage than your average magneto has revealed no problems that I am aware of, and I don't know of a manufacturer whose slipring products reflect the variations shown in the pix. Which isn't to say there isn't such a guru out there, natch, but I don't think there is any need for the different length segments for normal purposes. In cases where it is important to be able to position a brass segment in a specific way, there is a manufacturer in the Netherlands who supplies very handy kit-form sliprings which can be assembled with the brass strip wherever you like. The ones I have used are for Bosch instruments, and cater for parallel twin and V twin engines.
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Offline TimK

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Re: Magneto say Fuel - Spark = Bitch won't start ? Renamed
« Reply #48 on: 13.11. 2017 00:14 »
I've been reading through this thread to take advantage of the wisdom of the forum after my 59 GF that previously was a one/two kick starter died (luckily in the shed prior to a ride) and now refuses to start. The magneto that previously provided bright blue sparks to both cylinders is now providing nothing. I've worked through the advice already provided on the thread and the clincher seems to be the infinite resistance between the slip ring brass section and magneto body. If I've read Groily's advice correctly this indicates problems that are beyond my capabilities - can anyone point me in the direction of a magneto specialist in Australia who can help?

cheers

Tim
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Online Shark

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Re: Magneto say Fuel - Spark = Bitch won't start ? Renamed
« Reply #49 on: 13.11. 2017 06:16 »
Tim, the guru in Sydney is Chris Zoch.

Offline TimK

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Re: Magneto say Fuel - Spark = Bitch won't start ? Renamed
« Reply #50 on: 13.11. 2017 06:43 »
Thanks Shark, I've given Chris a call and will be putting my magneto in the post tomorrow.
Tim Kerridge
Australia

Online mikeb

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Re: Magneto say Fuel - Spark = Bitch won't start ? Renamed
« Reply #51 on: 13.11. 2017 09:29 »
Quote
Tim, the guru in Sydney is Chris Zoch.
+1 to that. Chris did a nice job and was super helpful rewinding my Mo1 earlier this year
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