T H E O L D G R E E N B E E M E R
RIDING A 1974 BMW R90/6 FLAT TWIN
POINTS? IGNITION SETTING
I like points ignition for simplicity and reliability. As long as you stay away with
file and sandpaper to " touch 'm up" they will serve you a real long time.
50.000 km at least, just keep the cam lightly oiled, every now and
then a tiny drop of motor oil is enough. There is no need to file
the points smooth in order to measure the gap, just eyeball
about 0,4mm of clearance and all is fine. This engine is
not critical on points dwell angle at all, so don't worry.
Points ignition: Simple, Reliable and easy to fix. By the way, two types of springs
are available for the ignition advance mechanism. Normal and stiffer, the stiffer
ones let the advance weights fly outward later in the rev range and so make
the bike easier to drive very slow like in parades for example, or trafic
jams and they make the bike feel more locomotive in the low revs.
Setting the timing is done by rotating the ground plate. The length of the cutouts
in the ground plate determine maximum adjustability, but you are free to
make changes. If for some reason you run out of room to adjust, what
can happen if you are using points of an aftermarket brand and are
contemplating to modify the cutouts, first try this: Just alter the
points gap to a slightly wider setting as long as you don't
go overboard in doing so, 0,6 mm is accepatable.
Just realize that increasing the maximum opening wil have an effect
on the lifespan of the lobe that rubs against the ignition cam.
Larger opening - longer contact - more wear - theoretically.
! Again do not forget to keep the cam / lobe lubricated !
I never use a strobe light to time the points anymore as most of the old boxers do
not give a good sharp image of the flywheel timing mark. The double image you
can see on these bikes can be caused by an ignition cam that is slightly off
180 degrees, or the ingnition cam is too loose a fit over the camshaft, or
the camshaft itself is not straight. My bike suffered the first and I have
regrinded one the ignition cam lobes. Practically I see no need
for a strobe light, I use an analog multimeter instead, reading
Ohms. The ignition switch can be left in the off position.
A piece of cigarette paper can also be used to time
the points but unfortunately only on a relative new
set, as these contact surfaces are still smooth.
Continue to Computer Aided Ignition Tuning
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IT rev 2021
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