Wandering ignition timing

[BSA Bob]

Something else to worry about with the R26.
The ignition timing has started wandering, by several degrees.
I set the timing, briefly run the bike & the timing's altered.
The points look OK, the points gap is firmly set & I make sure to secure the points plate properly after setting the timing.
Unfortunately there's some damage to the mounting slot for the advance unit meaning there's a lot of rotational play but I rotate the advancer against the direction of travel to take up the play.
Can someone give me any ideas as to what sort of fault I might have?

Bob

[BSA Bob]

[strichzwojan]

Maybe the woodruff-key on the flywheel was damaged or is missing, so that there will be false reading of the ignition marks, although the ignition still works well...

[4Taktix]

What Jan say's or also the plastic-bushing of the breaker lever could be slightly seized and pinch.
Or else your ignition cam is dry and a bit rough surface and thus the glide pad gets grinded a bit
and alters the timing over time.
Do you use a strobe to check timing ? Is the mark steady above ~ 3000 rpm or does it twitch ?

Regards,
Sascha

[BSA Bob]

Thanks again for the replies. I took the points out today, they're quite new & look fine, but the bushing Sascha mentioned was a bit longer then others I've got, I'd had  trouble getting the thin washer behind the retaining circlip that secures the points. So I shortened it slightly, reassembled things. Now with a strobe the F line is where it should be & doesn't wander, I'll be satisfied with that for now.
Is it a known problem for points to seize on their spindle? I'd have thought the spring would be powerful enough to overcome that.

[strichzwojan]

Thanks again for the replies. I took the points out today, they're quite new & look fine, but the bushing Sascha mentioned was a bit longer then others I've got, I'd had  trouble getting the thin washer behind the retaining circlip that secures the points. So I shortened it slightly, reassembled things. Now with a strobe the F line is where it should be & doesn't wander, I'll be satisfied with that for now.
Is it a known problem for points to seize on their spindle? I'd have thought the spring would be powerful enough to overcome that.

You can test it by inserting a 4mm HSS-Drill. If it moves freely its fine. But nevertheless you should apply a bit of grease to the bolt before mounting the contact.

[BSA Bob]

You can test it by inserting a 4mm HSS-Drill. If it moves freely its fine. But nevertheless you should apply a bit of grease to the bolt before mounting the contact.

I've greased the spindle & the points rotate freely. I wonder whether being pressed between the circlip, washer & the points plate may have caused them to be a bit sluggish,

[4Taktix]

at least it is plausible. It's often the tiny little details.

[rolf.soler]

You said the points look new. ARE they new ?
Did you replace them recently ? and why ?
Unfortunately, the quality of NEW points ist sometimes less than satisfactory...

[BSA Bob]

The points are an aftermarket set bought from a local supplier in Australia with a good reputation for things BMW. They've done about 3-4000 km & were installed as the previous set were old & pitted. I can't see any mechanical fault with them, all components are solidly mounted.
I think the excess rotational play may be a factor too. Today I checked the tightness of the advancer retaining bolt. The bolt head moved, it must've moved the advancer because the timing advanced so far the F mark was out of the window. I'm back to 42 degrees now & will make another test run.
I can't think of a way to keep the advancer stationary while tightening the bolt, all I do is hold it in position & hope.

[4Taktix]

Hi Bob,
the worn out notch for the advancer is a common issue.
Depending on how wide this notch is, you could twist the advancer clockwise in the notch and then tighten the bolt.
But then it may be, that the slot holes aren't long enough to bring the timing back to a proper setting.
These long holes can be filed a bit longer to a certain degree. Either it is OK then, or not.
If not, you can also set the point gap a bit wider, this also delays the timing slightly. ( or is it the other way 'round ? )
If still not OK, you probably have to think about reworking the notch.
-> welding spot, file, dremel-tool a.s.o.  -  fiddly but doable.

Regards,
Sascha

[BSA Bob]

Hi Sascha
Thanks for the opinions on the worn notch for the advancer.
As I said, tightening the securing bolt moved the advancer so I don't know where it sits on its mounting. If it doesn't move then I'm OK but I'll have to check things frequently.
There's enough movement in my points plate to adjust things, if I could work out a way to keep the advancer positioned against the direction of travel I should be able to set the timing reliably.

[4Taktix]

I'd say it moves clockwise by tightening the central bolt.
This is why I wrote to twist it clockwise until the little pin touches the edge of the notch.
This should give a reproduceable position. Or is this pin missing in your advancer ?
However, it is important that the advancer baseplate is tightened proper against the Dynamo-shaft while engine is running.
If so, you woun't have to touch this bolt for a long time.

[Kurt in S.A.]

Won't inertia cause the advancer to move the opposite direction of the motor?  If that's the case, then turn it opposite to engine rotation and tighten the bolt...hold the advance while tightening.

Kurt

[Kees]

No I don't think so. Tight is tight. It is while tightening that it can move.

[BSA Bob]

I think both sides are right here, it depends....
My first attempt was as Kurt suggests to turn the advancer against the direction of rotation because of the inertia. But I couldn't hold the advancer against the notch while I tightened things. Now it's somewhere in the middle....
To turn the advancer clockwise  would mean that it can't move further as I tighten . But would the centre bolt hold it there?
I should be able to get an idea about that with things as they are. Being somewhere in the middle, the advancer can move either way if the bolt doesn't hold it. I'll have to check frequently.

[BSA Bob]

The weather allowed me a short test run today, I didn't go over 80 in case the timing shifted again but it's stable on 42. So I'll see how Hildy goes next time out.

[4Taktix]

I wonder why you doubt the center bolt can hold the advancer tight.
Never had any issues with this or heard of.
You could use kind of locking varnish - at least you can easily determine then, if it moved or not.

[BSA Bob]

Hi Sascha
My only worry is that the way things are set up I don't really know where the advancer is set in its range of rotation (that it shouldn't have, of course). It probably isn't hard up against either end of the slot it sits in. So the locking bolt will have to do all the work. I thought it was best to make a medium speed run & check the timing. But the bolt seems to've locked things up successfully.