Advance and retard Cam stuck

[Sluggerslough]

Hi all on my Mod 31 650 1959 my Advance and retard Cam is getting stuck. I have fixed it earlier today but it has gotten stuck again after running briefly any ideas ? The cable works fine.

[Groily]

A common problem - and a one sentence answer would be good . . . but this can be more complex than it seems.
Here's the Quick Bit:
Usually it's wear on the 'mushroom' head on the plunger on the end of the cable; and/or the notch in the camring. At full A or full R the head disengages and things get stuck. Often a replacement plunger sorts it out. They're cheap - camrings are anything but.

If it's doing it at full retard, then cable adjustment might be enough to stop the plunger being hauled so far 'up' that it can disengage. (Losing a bit of retard doesn't matter if that's the consequence, you don't need half of what's there anyway.)

If it's doing it at full advance - slack cable - it's more sensitive. It may again be possible to limit movement 'down' using the adjuster but the downsides here are 1. that you'd lose your full advance position ref the igniton timing, so would maybe need to retime using the 'new' fully advanced position and 2. that there's no 'positive stop' of pin against camring at full advance, so some fretting is possible, which isn't great.

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Now for the Boring Bits . . .
. . but on the basis that one has to be aware of possible causes not just symptoms with these things . . . here goes:

Jamming is more likely to happen if the camring stop pin, which is eccentrically adjustable, is set fully one way, thus allowing the camring to move further than is comfortable in one direction or the other to the detriment of the hook-up of plunger to cam.
The stop pin is set to get the best spark at full advance with optimal INTERNAL timing of the mag (nothing at all to do with the ignition timing), and in an ideal world that pin would be in mid-position. It offers a few degrees of adjustment and was set at the factory when the mag was new, and on any subsequent rebuild (probably).
The pin is accessible if you remove the little pimple covering the head of the screw that turns it through its arc of movement. A sharp penknife or similar to get the pimple out is usually good.

One reason why the pin might be set fully in the advanced direction (against the rotation) would be if there were a lot of wear on the heel of the opening point, or on the ramps of the camring.
Wear on those causes the internal timing to retard ie the points to open 'late'. Ideally, the points, correctly-adjusted, should open a VERY few degrees of armature rotation (aka 'just') after the 2 'flip' points of the magnet. Delay weakens the spark - which gets weaker anyway as you retard the timing at the lever on a manual mag. But - the points HAVE to open after the 'flips' not before, or the coil won't be charged up and there'll be no spark. It's a delicate balance. It's also why ATDs are 'good things' however poorly designed they may be. They ensure the retarded spark is same strength as the fully advanced one, which for starting, and in the context of magnetos being inherently weakest at v low rpm . . . matters. It's a shame that the standard gear train doesn't allow an ATD option on our (pre-Notrun) twins - it's one area where 'the others' stole a march (Beesa, Notrun, Trihard etc) even if the so-called 'sporting rider' liked having knobs to twiddle and some models retained manual advance.

[Duncan]

I have also had issues arising from pattern clip on plastic end caps, some are missing the internal engagement tangs and the slip ring migrates out off the A/R wine glass/mushroom and wedges in the end of the magneto housing. The solution that is currently resolving this for me was to cut a thin cork gasket to go between the cover and the magneto body wide enough to prevent the slip ring moving out. An additional root cause could also be one of the reasons mentioned above or wear in the body holding the cam ring.

[Sluggerslough]

Thanks both for your reply. I will start with ordering a new cable as the adjuster thread had broken leaving on a small amount of adjustment. I went to HQ at Kettering this morning but he did not have one. I am pretty green when it comes to Ignition and magnetos etc so may need some help going forward. Sods law as someone was coming tomorrow for a potential purchase so this is annoying.

[g5wqian]

similar to duncans post check the cap on the magneto too , i have an alloy cap with stop button and have had issues in past with the screws holding it down coming loose .
i am using some small studs and long nuts [hexagon down to round form] , i put a small chamfer on end of nut and a slight countersink in the alloy casting although the casting doesnt have much meat there to make much of a countersink , the nuts have slots in ends as well as hexagon and i find much easier to undo and tighten up , as you may well know its all tucked down a bit too low for my liking .

dont run the engine without the cap on as the cam ring can come out when the points are spinning , if you want to run it up and have points exposed then get a spare cap and cut the face off so you have a "window " when its screwed onto the mag .

i did also have some trouble with my ariel NH advance/retard cable the other week but it was all down to cable being dry and locked up from my washing bike off at end of last year with some of that spray on cleaning foam that you leave on for a while then wash off , it must be that the cleaner gets into everything including cables , and the detergent is quite efficient .

i bought one of those cheap little £7 cable oilers you clamp to the top of cable and can fix an aerosol pipe into and squirt down into the end of cable , i used some ambersil TUF CUT oil and it worked a treat on all my cables .
mind you its that good a little tool [a bit messy and needs rag held over it if you dont want an oily hand ] that only a few squirts will get oil to bottom of cable .

i did have problems on an MO1L magneto a couple years ago where there was no return spring on end of cable by the shuttle and the cam ring only moved back and forth whilst engine was running , but luckily i found a spring of suitable size that fitted and sorted it out to get it working properly .

not sure about end of cable on the K2F cable though as i havent been out to look at mine ,although mine works fully .

hope you get it sorted out easily .
ian