Cam ring

[Mikey82]

After a k2f mag rebuild with aau and fitting on the GF the bike ran well for a mile then stopped.
I returned the mag to the refurbisher who checked it and found that the cam ring had moved.
I recieved the mag back and yet again after a mile the bike died again, after checking I see that the cam ring had moved again.
I,m going to use a strong loctite 271 and coat the outer cam ring and inner body and leave overnight hopefully this will solve the problem, forum searches suggest shims but I wouldn’t know where to get them.
Hopefully the loctite will solve the problem 🙏
Anyone else had this problem and found a solution?

[berger]

i thought a ATD mag had a cam ring with a locating peg so how has it moved? manual mags have a moving cam ring

[CheeserBeezer]

The points cover, regardless of which type should have an 'O' ring in the recess which stops the cam ring floating out.

[groily]

Having ensured you have the cover fitting correctly, might be worth also checking that the adjustable eccentric pin that's supposed to be in the notch has been properly engaged since the overhaul?
'Adjustment' fully one way or the other can cause failure to engage, especially if the pin in past its best. As can not screwing the pin far enough into the cb end housing for it to protrude enough.
Chances are it's fine on that front - but jumping camrings are far from rare, for whichever reason.

Ref the 'fit', with a fixed camring you don't want appreciable chatter 'twixt notch and pin, nor between ring and housing, so if your camring is actually a bit loose in its housing, further steps might be needed to get to 'perfick'.
I'd check the timing on both cylinders I think, to be sure things are as equal as possible. Self-adhesive shim tape in stainless steel is available down to one thou thin and is good for taking up slack between ring and housing (see eg https://www.dycartec.nl/en/shim-tape/a3511) - but you have to be very aware of the effect it might have on the firing interval between the cylinders and / or the points gaps.

[Mikey82]

Thanks Groily, there is no pin in the cam ring,( although it looks as though a hole has been filled in) it just pushes into the body, the refurbisher marked its location when he refitted last week after the bike broken down.
The cam ring moved approx 1” clockwise looking at points.
See pic of cam ring and body which is slotted

[groily]

Ah!
The pin is in the housing not the ring (at 6 o'clock, maybe sometimes at 12), and there should be a small notch in the ring that said pin slips into. Unless  . . .
 . . . maybe, your mag's got a tiny screw (or two off)  that go(es) 'longways', ie axially, into the inner face of the cb housing? Or the threaded holes for such - at about 4 o'clock looking in from the points end?
Some older K2Fs had this pair of 6BAs precisely spaced to take up the full width of the larger notch found on a manual A/R camring, so that the same ring could be used for manual or fixed camring mags. Later mags had a threaded hole with an eccentric-nosed setscrew screwed in from outside the housing. If yours was meant to have that, but hasn't, there'll be an 'ole, threaded 1/4 BSF from memory, in a small raised boss cast into the housing.

Whatever the case, there has to be something to locate the ring. You really can't rely on loctite or glue, it'll move for sure without.

Exact position is important for the quality of the spark, so with any luck your repairer has marked things accurately enough for you (or a mate) to maybe drill and tap a hole radially through the housing or axially into its inner surface to align with where the notch is. (Something he should have sorted out really, I reckon, if there really is no pin or other means of maintaining position.)

An inch clockwise displacement will have massively retarded the internal timing. That's well more than double the maximum retard available on a manual set-up - where the width of the notch is around 11mm.

Double check there isn't a pin or the threaded hole for one, or tiny screw(s) or empty tiny threaded holes, lurking in there before going off on a fresh journey  . . .

If you wanted to post a picture or two, it might be easier for us to figure out whether there's a problem, and if so exactly what it is!

EDIT - just looking at the pix

[Roger (Doomtrainbarx)]

Bill
How does shim tape affect the points gap/firing interval ?

[groily]

Right, at 1 o'clock in your first pic there is a removable (fine flat sharp blade, with more of less brute force to get it out) pimple on the outside of the housing. The housing has been fitted with it at the top. That pimple has a thin pin under its head which acts as an expander to lock in posiition the screw below, which has a deep slotted hollow head.  I can't see if the screw is intact and protruding or even all there (looks funny to me, but could be the angle), but its nose should go into the notch on the ring to locate it, then the end cover stops it falling out.
Is the pin there and does it engage the notch, and if it does, is the camring then aligned the way your man says it should be?
If there's a god then all should be well.
If it doesn't protrude, get the pimple off and turn the screw further in. If the pin is busted, you need another one. That can be had or made with just a file and some care!
If the alignment doesn't match your man's marks, come back and we'll have a think. But it should.
Good luck.

[Mikey82]

Attached is a better pic, Thankyou Bill you have made this a lot clearer, I believe it was you that helped me when confused with my Matchless G3 on the Ajs Matchless forum.
One pic with the arrow shows the nipple which is attached to the said pin shown on the second pic.
So if I were to smear some loctite on the outer cam ring, and fit so the pin sits in the hollow on the cam ring all should be well, does that make sense it should stop the cam ring from turning, and the new magneto cap cover with rubber seal fitted in the cover should stop the cam ring moving forwards…

[JulianS]

This is what the pin and pimple look like.

[groily]

Bill
How does shim tape affect the points gap/firing interval ?

Hi Rog, By shoving the camring one way or another relative to the housing - unless you can get a 360° wrap on the outside of the ring.
It's usually manual AR mags rather than fixed ringers that go a bit oval due to the incessant use of the same arc of movement, has to be said, and shim tape is a good and reasonably durable workround to correct matters. But if you start shimming on any camring / housing which actually has a correct interval despite a bit of fretting you can mess up what was correct to start with despite getting a better fit.

But if the job is to correct the interval / gaps (not the objective here) you have to start by knowing the bearing insulator on the cb end bearing is in good shape, as a problem there can cause all manner of hassle. Had a mate round here with a Dommie the other day with a 10° difference (crankshaft) between cylinders on the strobe - a new insulator and reseating the bearing got that down to 1° crank, or half a degree mag, with no messing around with housing or ring.

In this case, if the ring is loose, shimming may just be the best medium-term option, short of spending a shedful on a new housing or new ring, which will be £150 odd. But if you can't shim all round even with, say 1 thou tape, then there's going to be some sort of displacement risk, which is what we have to check / guard against. BUT - having seen the pix just now of this one - the first thing to do is fit the missing felt strip, nicely greased, in the groove and a pimple in the ring, and see if that creates a chatter-free or noticeably better fit - it often does, as well as offering some small level of lube going forwards!

[groily]

Attached is a better pic, Thankyou Bill you have made this a lot clearer, I believe it was you that helped me when confused with my Matchless G3 on the Ajs Matchless forum.
One pic with the arrow shows the nipple which is attached to the said pin shown on the second pic.
So if I were to smear some loctite on the outer cam ring, and fit so the pin sits in the hollow on the cam ring all should be well, does that make sense it should stop the cam ring from turning, and the new magneto cap cover with rubber seal fitted in the cover should stop the cam ring moving forwards…

Much clearer. You've got th right bits. As long as the alignment matches your man's marks or very closely, you should be fine, yes. I suspect you hadn't got the ring in the notch properly before, and then it moved outwards, etc etc, and went walkies. Twice!
Julian's pic shows exactly what's there. The pin is supposed to be set (and locked with the outer expander bit) to optimise the moment the points open relative to the change of magnetic flux of the armature. It's a very fine tuning thingamajig and in fact as points wear, or gaps change, the optimal setting isn't for ever. But your man has probably found the position that provides the best spark, and I'd stick with that as it's hard to pinpoint without having the right kit to figure it out!
You could use loctite if you wzere worried, but could make it hard to get out again. WHat I would do is find a bit of felt to fill the groove in the inside of the housing opposite the pin, grease it well, and the  stuff a tiny pimple of felt into the small hole in the camring. this is to lubricate the ring and the heel that opens the points - and also helps to eliminate freetting or chatter. ANy old bit of felt should do, and a Stanley knife or scalpel to cut a sliver to fill the groove  . . .

Then all should be and shall be well  . . .

[berger]

i am right in thinking the mag re furbisher didn't fit the felts and also put an end cap on that let ring move out? if so i'm never going there

[groily]

i am right in thinking the mag re furbisher didn't fit the felts and also put an end cap on that let ring move out? if so i'm never going there

Not uncommon to come across fixed ring ones that are felt-free bergs, but Lucas didn't make the groove  just for the hell of it! Points heel lube via pimple is good, and fret-reduction / absorption a possible side benefit. Nonetheless, a sparing smear of summat applied by dirty finger now and then is no bad thing, on any ring, and a more generous smear on the outside of manual ones is what I apply when doing routine maintenance on this 'oh no it's not fit 'n forget' instrument.

[Roger (Doomtrainbarx)]

Thanks Bill.
I just assumed that if you were going to do any shimming of a loose camring, you would be going for a 360 degree fitment.