Differential timing issue

[bigdave]

Working on a 1958 R60. Now putting it back together as per the Barrington "Bible". It is showing timing issues when trying to set the timing. Rotor is set and rest of the magneto is installed. Point gap set correctly. Using a dial indicator on the advance mechanism, the lift of each lobe is within .001. Rotating the engine 360 degrees and watching the meter to see when points open, the timing is off almost the full window where one views the timing. I did try the "tap on the bolt" as specified by the bible, but saw no improvement in the differential and that is when I tried the dial indicator to see what was wrong.
Does anyone have an idea of what I am doing wrong here? I have a 1965 R50/2 that I built successfully, so this is not my first go with an old BMW.
Any ideas appreciated.
Dave Fish in PA

[Rodolfo850]

Check your points,

I just has same issue on my R60/2 few weeks ago, I wasn't able to correctly fit time.

Magneto time was correctly set, point gaps set, but can't make test Buzzer lights when flywheel shows S on mark.
When making a running timing test, S appears on upper side of window (too Advanced), but points didn't go far enough to retard time a little.

Even moving magneto body( knowing that will weak spark) didn't make any difference.

After three days I started to make some test with point gaps, while measuring find that point gap changes between engine rotations, meaning differential timing is affected by point gaps. Checked with a Dial indicator and all its OK...

Until removed ignition point and find that pivoting bushing isn't concentric, with a 0.10 mm of runout on middle, so at some point rotated perfect with a bore of 4.00 mm but when hits oval part of bushing diameter increases to 4.10mm which causes a reduction of point gap, causing problems on timing.

After installing a used set of Bosch ignition points, everything works great!!

Start by changing ignition points set and check again..

regards

Rodolfo

[bigdave]

Thanks for the points suggestion, but no joy. Same difference with the old point set.
Thought that maybe it was the advancer, so took one off my running R50. Installed on the R60, but acts the same.
Suggestions are welcome.
Thanks in advance.
Dave

[skychs]

Have you checked the Advancer? One of the guys in our group had the same issue. It ended up being the advancer.
chuck

[808Airhead]

I have been successful eliminating differential timing by using a brass drift and a hammer, brass drift resting on the side of the advancer/ allen bolt , hitting it toward the "retarded/late side",very careful, yet purposeful hit with hammer. I have been able to get timing differential within a millimeter or less in the window. Change your technique (?) I use a aviation magneto timer, and this helps a lot!

[jwonder]

After reading through the thread, you have done all the standard checks and this is likely a bad cam lobe. Timing is not controlled by the height of the lobe, but when the lobe "starts" (in other words, the ramp of the lobe).

If this is a replacement advancer they have been known to be bad and I had a very bad one that was new. The reproductions have been bad for a while and I am not sure when they were introduced! Please see a video I made on the issue and it clearly shows the height is close, but the ramp starts in the wrong area. viewtopic.php?f=7&t=16364

Now, if it is an original unit I would be surprised if the ramp was worn, but if proper lubrication was not used throughout its lifetime it could certainly be worn, and only one lobe, not both. It is possible.

I hope this helps!!!

[Daves79x]

If you keep at it, the hammer-and-drift method will get you close. The mag rotor very often does not seat perfectly concentrically on the cam. You are just whacking it to a more central position. I've done it to both of mine and now have virtually no differential timing.


Dave

[sherman980]

Over the years, I've used the hammer-drift method on the OEM advance units occasionally to help them "seat" properly and had some success with it. I purchased a reproduction unit about five years ago, and as James identified above, the actual cam profile is "off" and you can bang away and never get it right. Once I determined that the cam was "bad", I figured I had nothing to lose, took it apart, and used a knife sharpening stone to reshape one side of the cam. This actually worked pretty well and that bike is still a 1-2 kick starter to this day. Just a thought to make a useless part useful...

Hope that helps.