K2F Magneto Strip

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K2F Magneto Strip

Postby Mick D » Thu Jun 06, 2019 6:51 am

Hi

I'm in the process of inspecting a Lucas K2F magneto - following the Lucas Workshop Instructions and the guidance on the Brightspark website. I have removed the long bolt that secures the CB inside the ring cam but can't free the CB assembly from the armature, (the Lucas manual suggests there is a keyed taper to be separated), is there a knack to removing the CB assembly that I'm missing?

Regards Mick

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Re: K2F Magneto Strip

Postby Dixter » Thu Jun 06, 2019 7:39 am

Hi Mick, using the same screw you removed to secure the contact breaker assembly (CB) return about half its length back into the contact breaker, and with light pressure, wiggle the outer end of screw around in a 360 degree circle, levering the CB assembly towards the cam ring. The CB will promptly release from the taper.

Ciao, DC
Dick Casey
The RideNut

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Re: K2F Magneto Strip

Postby Mick D » Thu Jun 06, 2019 8:21 am

Hi Dick
Worked a treat - thanks very much :beer:

Regards Mick

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Re: K2F Magneto Strip

Postby Mick D » Wed Jun 12, 2019 7:02 am

Hi

The magneto investigation is progressing well, it's now in 'kit form' and I'm going through the electrical tests while I wait for the aluminium sheet to arrive which will allow me to fabricate the pullers for the contact breaker end bearing inner race and slip ring. (Thanks Brightspark for the drawings on your website :beer: ).

A couple of questions for those who have been here before:

I am seeing an open circuit when I check the resistance of the HT winding, between the slip ring contact and the armature - could this be a case of the HT 'spike' not making contact with the slip ring where inserted? (Once I have the slip ring off I'll be able to diagnose the circuit from the spike to the armature).

The contact breaker end bearing outer to CB housing resistance is only 0.3 Ohms, indicative of the insulator having broken down, so I'll replace that on assembly but I am wondering what the purpose of the insulator is. Would it be correct to say that the function of the insulator is to prevent arcing within the bearing by isolating it from the return path?

Regards Mick

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Re: K2F Magneto Strip

Postby Groily » Wed Jun 12, 2019 10:30 am

Hi Mick,
Ref the Open Line reading on the s/ring to spindle, could be that the spike isn't well in the slot or is damaged, yes. But stand by to find an open line coil, which may still spark, but it's all downhill! Should be round about 5000 ohms typically on a K2F.
You're quite right about the insulators - they are there to stop return current going through the bearings, hence the fitment of the earth brush to do the job. If the brush is OK, probably saves the bearings from being eaten, but the cb end insulator needs to be well fitted to ensure the outer race is concentrically placed, and not screwing up the firing interval between the two cylinders by being offset. A little error goes a long way here!
The return to earth can happen in loads of ways, with steel gears for a start (as opposed to fibre ones on some other marques) but always best to have things how they're meant to be.
Good luck!
Bill

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