Forum bmwbike.com

hello everyone.

my 1956 R60 runs perfect but the engine stops at idle after a sudden coughing noise. i have checked the carbs and fuel flow. everything seems to be fine. i have some doubts about the magneto. the firing time and advance are o.k. but the contact breaker points do not open evenly (.35mm on one side, .50mm on the other). could this be the cause of the stopping? what are the other possible causes?

thanks

Maybe the variation in points gap is making the timing of the two cylinders different. When you look at the S mark, you might only be seeing the mark for one cylinder, with the mark for the other cylinder far out of sight.
If this were so, then the bike might idle poorly, running mostly on the first cylinder to fire. If that cylinder mis-fired, then the engine might cough and stop as you experienced.
Maybe the variation in points gap is caused by an advance unit that is mounted poorly. Try removing the advance unit and reinstalling it carefully.
Or maybe the variation in points gap is caused by a lot of runout in the camshaft -- the camshaft carries the advance unit which opens the points. Runout might mean that the end of the camshaft is bent.

Try raising the idle speed of the engine. It will not cure the problem with the points gap, but it will reduce the tendency to cough and stall.

Why do you suspect the coil is bad? Usually when original coils go bad, the bike becomes hard to start when cold, and then will not start when the engine is hot.

Maybe the variation in points gap is making the timing of the two cylinders different. When you look at the S mark, you might only be seeing the mark for one cylinder, with the mark for the other cylinder far out of sight.
If this were so, then the bike might idle poorly, running mostly on the first cylinder to fire. If that cylinder mis-fired, then the engine might cough and stop as you experienced.
Maybe the variation in points gap is caused by an advance unit that is mounted poorly. Try removing the advance unit and reinstalling it carefully.
Or maybe the variation in points gap is caused by a lot of runout in the camshaft -- the camshaft carries the advance unit which opens the points. Runout might mean that the end of the camshaft is bent.

Try raising the idle speed of the engine. It will not cure the problem with the points gap, but it will reduce the tendency to cough and stall.

Why do you suspect the coil is bad? Usually when original coils go bad, the bike becomes hard to start when cold, and then will not start when the engine is hot.

Thanks Allan. I thought that the camshaft was runout and didn't draw attention on the advance assembly. but when I checked the unit, I realised the problem is with the centrifugal advance unit. It does not properly fit on the magnet. The cam gap on the magnet is in poor condition and thus it keeps the centrifugal advance unit off center. Is the only way to correct this issue is try to patiently center the centrifugal advance unit or is there another way?

best wishes.

"...The cam gap on the magnet is in poor condition and thus it keeps the centrifugal advance unit off center. Is the only way to correct this issue is try to patiently center the centrifugal advance unit or is there another way? "

There is a little notch on the end of the magnet rotor, into which fits a tab or key on the advance unit. I understand that your notch and tab have probably been mashed together by careless installation, causing a lot of play in the fit.

Fit the advance unit carefully, to be sure the tab and the notch are mated. Then, instead of centering the advance unit, turn the advance unit one way or the other way, to the limit of the slack. Then hold it while tightening it. Thereafter, when removing and replacing the advance unit, as when turning the points plate, always turn the advance unit the same way to its limit, and hold it there while tightening it.

ok Allan. thanks a lot.

best wishes.