Author Topic: K2F Slipring problem  (Read 216 times)

Offline Peter Gee

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K2F Slipring problem
« on: 28.09. 2019 06:29 »
Hi..having a real problem with my home-rebuilt and well running K2F Manual advance model on my A7SS. After operating the advance/retard once or twice, it studdenly "sicks". This is not a cable problem but the  cable with screw in, spring loaded abutment are new repro parts.

The only remedy is to take the  plastic cover off, pull our the slip ring and re-fit it. Then it happens again. I suspect the little foot of the lifter, which is a pattern part, may be of wrong diameter aand not properly engaging in the slip ring slot.

Anywane else had a similar prob? Have had magnetos for many years but this is a bit baffling.


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Re: K2F Slipring problem
« Reply #1 on: 28.09. 2019 08:05 »
Could well be the foot on the plunger Peter, or a bit of wear on the notch on the CAMring. (Not the slipring, that the plastic bit inside that the brushes track on).
If the plunger is part-disengaging or jamming at one end of its travel or t'other, that's the most common problem.

Check the edge on the camring cable notch is good, and clean up if need be - very gently.  If the plunger can't seat fully 'in', then it will jam in certain cases when operated - in which case tweak the mushroom foot to get a flush fit.

Most common problem is that at the limit of ring movement the plunger slips out of engagement because the camring geometry is off kilter. Could be the eccentric stop pin that controls camring movement could be adjusted a fraction to alter the ring's relative position to the housing - and improve the geometry of the plunger - but the pin's main purpose is to fine-tune the internal timing of the mag, not get round a cable / plunger problem. (Points should open just a tiny handful of degrees after the magnetic flip, at full advance - delay retards and weakens the spark, too early kills the spark as the coil won't have charged up). There is some leeway though and if a compromise is needed to get the camring to operate correctly, then so be it in such circs.

Worst case, if the problem persists, you could grind new notches on the opposite sides and 'start again' with the geometry. First thing to do there is establish where the ring wants to be at full advance (points just opening after flip, etc).  It will be close to 180° opposite, but not quite (or we wouldn't be doing this!)
Cut a small notch big enough to fit the stop pin only. Offer up to housing, with eccentric pin in its central position. See how close to optimal the points opening position is ref the flip. If happy, enlarge notch to provide retard. If not happy, provide a tad more advance, check again and then grind for retard.
When happy here, cut new cable slot. Set camring to mid-position in housing and mark to cut slot so as to have plunger foot at mid-position too. Then you get best angles at full extent in both directions, and least chance of disengagement.
Fine tuning by the eccentric pin is still an option, but probably not necessary.

Best to do this, if you have to go this route, using a new opening cb point - as wear on the fibre heel affects the optimal setting of ring by a good few degrees. You wouldn't want to use a worn heel, set it all spot on, then find next time you changed the cb points for new the mag was over-advanced and sparkless. It happens!

Worth also ensuring that if there is meant to be a gasket stopping the camring from sliding axially out of its housing, it is there. Or that the little plastic footings on the inside edge of the plastic cover are making contact with the ring to keep it snugly in place.

It's quite a common problem to be honest, but can be exasperating - and a consequence of several small things rather than one obvious one.
Bill

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Re: K2F Slipring problem
« Reply #2 on: 28.09. 2019 09:28 »
It’s not an unusual problem with that ramshackle mechanism.

How about just not retarding it so far with the lever?  Assuming it’s the slack wire advance type, if you adjust the cable to have a lot of slack, then it can’t pull the cam ring very far and maybe the nipple will stay in the slot.

Online berger

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Re: K2F Slipring problem
« Reply #3 on: 28.09. 2019 19:29 »
Peter Gee I had a problem with mine sticking when I bought a new cable and after much scratching of the bonce I found that when the control barrel was screwed into the mag body it was nipping the control plunger even though the spring was good. as soon as the control barrel was nipped up it was jamming the plunger. I had to ease out the control barrel to stop it locking the plunger up. my really old other cable is tatty but works perfectly. the new pattern part was the problem it worked until it was nipped up onto the mag body then once tight locked the plunger up. hope this helps *beer*

Offline ironhead

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Re: K2F Slipring problem
« Reply #4 on: 28.09. 2019 22:02 »
Peter Gee I had a problem with mine sticking when I bought a new cable and after much scratching of the bonce I found that when the control barrel was screwed into the mag body it was nipping the control plunger even though the spring was good. as soon as the control barrel was nipped up it was jamming the plunger. I had to ease out the control barrel to stop it locking the plunger up. my really old other cable is tatty but works perfectly. the new pattern part was the problem it worked until it was nipped up onto the mag body then once tight locked the plunger up. hope this helps *beer*


Pattern parts, pattern parts, pattern parts  *angry* *angry* *angry* *sad* Bought an advance cable recently
& had to shorten the over length spring ( getting coil bound ) then rethread the plunger housing as it was waay too tight & nipping up the plunger. By the time I re-built  it I would have been better off making a new cable & fitting the old plunger assembly.
SA

Online berger

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Re: K2F Slipring problem
« Reply #5 on: 28.09. 2019 22:38 »
ironhead , same as mine then. mine went in easily but nipped up the plunger as soon as the barrel was seated on the mag body *bash* *problem*

Online mikeb

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Re: K2F Slipring problem
« Reply #6 on: 29.09. 2019 10:17 »
my SR did this too when i first got it. with the mag end cover off, what i noticed was as the cable operated and the cam-ring turned, the cam-ring was also pushed outwards slightly into the small gap between the outer of the cam-ring and the end of the body (ie under the end cover). when it moved outwards it jammed - same as yours.
my temporary 'fix' was to cut a 'washer' shaped piece of plastic (from an old food container) to sit outside of the cam-ring and up against the end cover. ie to stop the outward movement - but not jam the cam-ring. imagine a 0.5mm thick washer - OD the diameter of the cam-ring with id about 3 to 4mm less (so it does not interfere with the points).
i'm not sure why the outwards movement happens - no one else talks of it.  tho the plastic temporary fix has worked since so it is still in place.
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