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Garnet wrote:Did you get the correct sprockets? In 78 they advanced the cam timing by 6 degrees. I believe they did that by moving the key slot in the cam sprocket. If you got a 78 cam sprocket then maybe that's the isue.

I know the Quinner swears I'm wrong, but when I stack a 71, a 75, and a post 79 sprocket the teeth and timing marks all line up. It was my understanding that the cam's slot was moved not the sprocket's. I could be wrong, (not sure how)I've seen it with my own eyes. I even used a double chain on two sprockets at the same time to make sure the teeth were aligned.

But then why would the sprocket part numbers for the different years be different?
Only recalling an earlier post in this thread...
It would be a lot easier to change the keyway in the sprocket, too, in the event you wanted to mess with the timing for different countries of delivery. NOT that BMW would choose the easy way....

esman100 wrote:

Native /5 wrote:I can see how the height of the rubbing block would affect the point gap and thereby the timing, to a small extent. But, the point gap adjustment is approximately in the middle of its range, before I set the timing.

Having thought of this subject prior to posting here, I could give this scenario much more credence if the position of the rubbing block were off, rather than the height. All of my point sets (5) appear to have the rubbing block in the same position.

I have another set of points bought at the same time from the same source (Hucky) in my '77RS, without this issue.
I don't mean to be contrary, and I'm not too upset since the bike runs so well. I'm just curious if others have seen this anomaly and what they did to correct it, etc.

I know for a fact some BMW points came in with the height of the rubbing block too high and this effects the position of the points plate orientation even when set to .014-.016" gap. I had the same timing symptom that you are getting and I ended up filing out my plate to get close until I figured out the real problem. This was confirmed later by our local dealer after many complaints. I'm not saying that your points are bad, but it seems possible that even though they came from the same supplier, one could be bad. It's easy to measure and very obvious in a side by side comparison. The bad points are approximately 1 1/2 mm taller.

I don't question your assertion that some points' block were higher. This affects the point gap. It does not change the position of the bump on the cam. Once the point gap is set correctly the relative height of the block is moot.

Native /5 wrote:

esman100 wrote:

Native /5 wrote:I can see how the height of the rubbing block would affect the point gap and thereby the timing, to a small extent. But, the point gap adjustment is approximately in the middle of its range, before I set the timing.

Having thought of this subject prior to posting here, I could give this scenario much more credence if the position of the rubbing block were off, rather than the height. All of my point sets (5) appear to have the rubbing block in the same position.

I have another set of points bought at the same time from the same source (Hucky) in my '77RS, without this issue.
I don't mean to be contrary, and I'm not too upset since the bike runs so well. I'm just curious if others have seen this anomaly and what they did to correct it, etc.

I know for a fact some BMW points came in with the height of the rubbing block too high and this effects the position of the points plate orientation even when set to .014-.016" gap. I had the same timing symptom that you are getting and I ended up filing out my plate to get close until I figured out the real problem. This was confirmed later by our local dealer after many complaints. I'm not saying that your points are bad, but it seems possible that even though they came from the same supplier, one could be bad. It's easy to measure and very obvious in a side by side comparison. The bad points are approximately 1 1/2 mm taller.

I don't question your assertion that some points' block were higher. This affects the point gap. It does not change the position of the bump on the cam. Once the point gap is set correctly the relative height of the block is moot.

I believe it may change the position on the cam because it changes the angle to the points which may cause it to hit in a different location on the cam. I do know how to set points properly and can tell you that the longer block was not timeable with the standard slots. It is posible that the location of the block front to back was off too. I didn't think to check for that and I don't think that I saved the bad points to verify.

Jean wrote:But then why would the sprocket part numbers for the different years be different?
Only recalling an earlier post in this thread...
It would be a lot easier to change the keyway in the sprocket, too, in the event you wanted to mess with the timing for different countries of delivery. NOT that BMW would choose the easy way....

The sprocket numbers change because.....first the mechanical tach gear is deleted, and then after that, they go to single row chains. The cams were changed significantly (the nose was cut off and the oil pump end lost it's keyway completely). A new cam design with a new keyway slot for timing. My understanding is that all bikes with bean cans have 6 degree advanced cams.

I forgot about the mechanical tach, which occurred between 1977 and 1978 on the R100 series.
When did the single row chain show up? Everything I have has double row chain.

Static-Dynamic timing (2nd try)

Here's a timing method I've used for years on my R75/5.

Buy new points and condenser. They're cheap.

Remove spark plugs.

Remove rubber plug on the timing "window"

Check key off.

Remove front cover.

Remove old points and condenser and install new ones.

With Allen wrench in the alternator, rotate the engine until the points open at their widest. Set points gap with the feeler guage in the tool-kit, and tighten the screw.

Rotate the engine until the "F" mark is in the timing window.

Key on. You can now hear a "snap" when the points open (and also see the spark).

With finger/thumb, move the bob weights on the advance unit to their wide open (fully advanced) position. If the timing is perfect, the "snap" will be heard exactly when the bob weights reach the wide open position. You will likely have to loosen the screws and rotate the timing plate a bit to achieve this, but it is possible to get this very precisely. Tighten the screws and check the adjustment again.

Key off.

Replace front cover.

Re-install spark plugs and replace rubber plug.


jtoml

Calgary
R75/5

Neat trick, jtoml!

I'll give it a try next time I'm in there. II'll prolly have to file the points plate slots to get there, though.