Vintage BMW Motorcycle Owners

Can someone humor me about how the timing cable hooks up to the magneto. I've included some pics of what mine looks like. (I already took the cable off) I'm just sliding the end of the cable thru the two round tabs with the barrel end attached. however, it occasionally slips out. I'm beginning to think I missed something. For instance, what is that little black screw for? or just a safer setup...

Also, I've noticed there's an external spring added to assist returning the timing to the retard position. ok, but are you suppose to hold the timing advanced when at higher rpms? Do i need more compression on my control lever to hold it?

Thanks,

J

On mine I have another end on the cable, it's more like a small lead cylinder soldered on, that slips between the two round brass tabs. At the bottom of the tabs there is a hole drilled where the lead cylinder goes to not slip out. Perhaps your end is the correct type, I don't know.

The little black screw is to tighten the strip on which the round tabs are mounted. The strip can be positioned so that the round brass tabs are in a suitable position for advance/retard. Possibly also to position it so that the cable doesn't slip out in full advance position.

The external spring assists the returning to ADVANCE position, that's at higher RPMS. I've found the original spring is too strong so my advance control lever wasn't staying in a fixed retarded position at startup. So I've put in a weaker spring. Normally at higher RPMs the external spring is relaxed - you shouldn't have to hold the control lever during riding.

PS I saw some people using the cable slack adjustment to fine-tune timing, but I found that isn't necessary. The coarse setting is the position of the sprocket of the magneto relative to the sprocket on the camshaft. That can be impossible to get into spec, so there are magneto sprockets which have two differently positioned splines which allow rotating on the magneto axis half a tooth. Then the fine tuning is done by slightly adjusting the points gap (0.05mm or so differing from spec).

Thanks Pkrpkr,

I think that makes sense. Do you mind taking a picture of your setup just for reference? I Appreciate the response.

J

dBDawg, is your bike an R12 or a chain driven magneto R11? It looks to me like you have a magneto that is set up for gear drive. Your advance cable is mounted on the left side, not on the right side like pkrpkr's magneto. These magnetos are very modular and can run in either direction, and with a variety of cylinders and cylinder configurations, depending on how they are setup. Bosch was very clever about how they built these D type magneto units. Any way, you may have one that is set up for the earlier gear drive that turns the magneto in the other direction.