Vintage BMW Motorcycle Owners

Glad things worked out. Maybe this will be a source for others in the future.

As for checking differential timing, there should be a need to move the timing light from one lead wire to the other. Either spark plug wire will surge whenever the points open. Since the system is wasted spark, both spark plugs fire whenever the points open. One of the flashes will be for spark on the compression stroke and one flash will be on the exhaust stroke for that cylinder...but the points were opening for the other cylinder on the compression stroke. Basically you should see the same thing no matter which side you hook your timing light up to.

Kurt, right you are. I just thought I would go from one side to the other just to see if I saw any difference. I didn’t. Plus I wanted to make sure that both sides were sparking!

Kurt,

You are right, the height does not matter, it is when they open. So it looks like you got a usable one and I got oine of the bad ones. I think it comes down to their grinding machine and quality control.

As you said, 1/8" should not matter very much. Its good to know you fixed your problem!!!

Could you have used the new parts with the old cam?

jwonder wrote: ↑

Thu Aug 19, 2021 1:35 pm

Kurt,

Could you have used the new parts with the old cam?

I believe so. And that is what I was going to try next if the differential timing was too far apart.

You lucky b...d Kurt.

My 'new' unit didn't work right, even after exchanging parts with the old one. New Noris points also were different from original. They are slightly higher and once in a while would contact a metal part and ground. Although I prefer mechanical ignition there was too much fuss with the engine getting hot.
Installed Vape electronic ignition after finding out it doesn't need a battery to operate and the engine starts, idles and runs very well now. Hopefully someday we'll have better advance units but until then I'm not going back.

Kurt,
Where did you buy your advance Unit? I find one in stock @ Boxer2valve but not Salis or Benchmark currently. Is there only one manufacturer for the after market unit, so it doesn’t matter who I purchase from (other than price perhaps)?

I’m hoping to borrow one from a buddy for diagnosing purposes before purchasing.

Thanks,

Chris

Despite attention by several skilled mechanics and replacement of critical parts (condenser, points, coil, lead wires, etc.) my 1964 R69S does not want to start. She fires right up when bump started and runs once started. The bike starts fairly well for others, but is reluctant to start for me.
It has an aluminum flywheel that is marked ~12˚ retarded. We indexed it and marked the flywheel with more accurate marks. At times, use of a strobe timing light shows marks on the flywheel; however, other times the light shows only a blur.
There seems to be adequate spark. We bypassed the magneto with a 12 volt coil & battery and got a hotter spark; however, that did not make it start any better.
It seems to me that something causes the timing to flop around, especially at very low (starting) engine speeds. Could this be caused by something amiss with the advance mechanism? If so, what precise part is the most likely culprit?

It has also been suggested that the starting problem might be caused by excessive overlap with the cam or by poor carburetors. That seems unlikely because (1) the problem is intermittent and (2) the blurred flywheel markings would not be caused by valve overlap or by poor carburetion.

What do you think: Could this starting problem be caused by a mismarked aluminum flywheel and a bad advance mechanism?

The bike starts fairly well for others, but is reluctant to start for me.

That sounds like a technique issue with what you're doing. You could figure out what they are doing that is different than you.

My guess is the issue is with the advance unit. The flywheel is solid and doesn't move around. It might be mismarked, but it is what it is. The light from the timing light is being triggered by the points opening/closing which is the advance unit. So, it's probably pretty sloppy and worn out.

A couple of thoughts. When you install the advance until onto the camshaft nose, are you properly and securely locating it into the detent on the end of the camshaft? It should be installed so that the nub is in the detent and then you should turn the advance unit opposite to the direction of rotation to push it into the far side of the detent. That way it doesn't move around in operation.

Second, are you using a standalone battery for the timing light? Using the battery from the bike is generally not a good idea.

Sure enough: It was the advance unit. I replaced it with a better one I had on hand, and the bike starts just like it should. There are a lot of other things that need help on the bike, but at least it runs now.

Great information. Thanks for posting. I had a similar issue with my R60/2.