Limitation of Advance

[Peter D. Nettesheim]

Kurt,
You are getting much too involved with making changes and replacing "caro" stop screws and checking all sorts of things without understanding the system. I was trying to understand what you were writing about but the first thing I need to bring to your attention is that your understanding of the timing is backwards. I think we need to first get you straight on this and then maybe all else will fall in place. First "F" stands for Fruh or early (not "Basically retarded" as you seem to believe and stated in your message) It is the oppisite, it means full advance. The "s" which is not mentioned in your message stands for spat or late meaning retarded. The timing advance works on the principal that as the engine increases in RPM the weights float out and advance the timing (not retard it). You message shows a belief that the system works differently.
This explaination should help you understand the basic workings. Using this, see if you can now time it correctly. If not pose the question in a way that takes this normal operation into consideration. Good luck and write.
Peter D. Nettesheim

[Allan.Atherton]

... been having trouble getting anywhere near full ignition advance on my R69S.... When I jamb open the advance weights, the points open about 10-15mm before the F-mark is reached, which results in running retarded. I've confirmed this by using a timing light. I see the S-mark at idle but I can't see the F-mark in the window when I run the RPMs up to say 3000....
I just use a strobe light, and don't know about doing it statically as you describe.
What happens above 3000 rpm? My bike is not fully advanced at 3000 rpm, but is at 5500 rpm (on a TinyTach). There is some debate over where full advance is supposed to occur, but my bike runs fine. It is an R69S with a new advance unit (Huggett 2001) and a Caro stop.

[schrader7032]

Peter -

I'm sorry if my post didn't explain things well. I believe I fully understand the ignition system, the timing marks, and how the advance is supposed to work. The F-mark is the point on the flywheel which represents full-advance at some degrees BTDC...I don't know what the degrees are. The S-mark is what, 6 degrees BTDC?? At idle, the S-mark should be in the window (typically) meaning that the spark plugs fire in advance of TDC so that the flame front has time to burn but not burn too early to meet the piston on it's way to TDC. If the point of ignition is too advanced, then the result is pinging which is not good. If the point of ignition is too late, then a lot of the explosion from the combustion is lost out the exhaust valves as they will begin to open.

My general understanding, mostly from my /7, which I think should apply to the /2, is that, ideally, the S-mark should be visible in the window at idle (either by static timing or by timing light) and that, as the RPM is increased, at some point the F-mark will appear in the window. At any higher RPMs, the F-mark will not move anymore but remain firmly in the window. This is the point of maximum advance as a result of the weights swinging out on the advance unit. I've heard that too much advance on an R69S will result in pinging and holing of the piston. On my /7, full advance is achieved around 3000-3200 RPM. On the /2, it is probably in the same neighborhood...I don't have a tach.

As Allan suggests, the best thing to do is to monitor things using a timing light. But you have to start somewhere, and that is usually by setting the idle timing point using a voltmeter to monitor when the points open. I did that to put the S-mark in the middle of the window as the points open. I believe the reason to do this, for the most part, is to get the engine to fire at kick start...along with having the magneto set to the abrisz(?) point...which I have done correctly and recently rechecked.

In my case, using the timing light, I see the S-mark in the window at idle but as I increase the RPM, the S-mark moves out the window towards the top. I increase the RPM to some higher value, probably around 2500 RPM but I never see the F-mark. There is a small scratch on the flywheel that I've seen rotating the engine by hand...the scratch is positioned somewhere between the S-mark and the F-mark. At the elevated RPM, I see the scratch when viewing with the timing light. The scratch remains steady in the window as I continue to increase the RPM. My only conclusion is that I have reached full advance at the wrong point. Based upon where the ignition is firing relative to the F-mark at full mechanical advance (ie, with the weights completely extended), I am running in a retarded mode at high throttle settings. To me, that doesn't seem right.

After much thought and additional discussion on the /2 forum, I have relooked at my advance unit. It is fine, no ovaled posts, no stiction...it is a perfectly good advance unit. It's just that the point of full advance does not allow for proper timing at high throttle settings.

With nothing else to go on, I approached this from the other end. I performed static timing of the bike with the voltmeter to have the points open when the F-mark is in the window while the advance unit was at full advance. Other's have missed my point, here. I manually set the advance unit so that the weights are at the full extreme. In this situation, the points should open at the F-mark. This is done statically with the voltmeter.

After setting the bike in this manner, I started the bike and used the timing light to verify the settings. Just as I suspected, at high throttle settings, the F-mark is slightly below the timing window...good enough for me. I checked the timing at idle. The S-mark is near the top of the window IIRC. Not great, but the bike starts well and idles OK. I went for a ride and the bike did not perform dramatically better, but it did not ping. I think that's as far as I'm going to take this.

I hope I've explained my situation well enough to give the impression that I understand the ignition and timing process on the bike. No doubt I could use the hands from a guru on this, but I think I've done all I can do for now, other than ride the bike and see how she performs.

If anyone has any additional comments or thoughts, I'm all ears. Thanks for hanging though my thought dump!!

Kurt in S.A.

[Allan.Atherton]

... When I jamb open the advance weights, the points open about 10-15mm before the F-mark is reached, which results in running retarded....
I just use a strobe light, and don't know about doing it statically as you describe....
I mean, I do set timing statically first, but it had not occured to me to jam the weights open to rotate the cam to where the points opening will show where full advance will occur.
I can see that would show on the flywheel where full advance was, without running the engine, but it might not be as accurate as actually running the engine with a timing light. Did you find it just as accurate?

[schrader7032]

Allan -

Yes I did. The points opened at the same visible location in the timing window, either by static timing or by using the timing light. As I look at it, I can't see how it would be otherwise. In either case, the location of the flywheel at the time when the points open is what it's all about. If I jamb open the weights, and do the measurement with the voltmeter, it just seems that it would be the same as when the weights float out due to the rotation of the advance unit. Of course, there might be some differences, but I feel it would only be minor, if even measureable. That is what I discovered when I used the timing light. It seemed to backup the static measurements.

Kurt in S.A.

[VBMWMO]

I posted this on the /2 forum...thought I'd see if anyone had any ideas over here...

I've been having trouble getting anywhere near full ignition advance on my R69S. I've checked static timing with a voltmeter and it's about as close as I can get. I decided to spread the advance weights to their maximum and recheck to see when the points open. They open well in advance of the F-mark (basically retarded timing). My advance unit looks like the one Duane Ausherman's pictures here:

http://www.w6rec.com/duane/bmw/advance/advance2.JPG

except that I replaced the newer u-spring with the "Caro" stop screw. The Caro stop screw replaces with spring in the picture with a simple screw and jamb nut...it's a hard limit on the amount of advance rather than relying on the resistance of the spring.

What I've noticed is that the post on the other weight (right one in the picture) bottoms out in it's groove long before the other post (left one in the picture) comes into contact with the stop screw. And since the two weights are interconnected via the center section which rides around on the camshaft, the non-stop screw advance weight limits my ignition advance.

Other information...I used the voltmeter process to check exactly when points open when the advance weights are moved to their extreme position. When I jamb open the advance weights, the points open about 10-15mm before the F-mark is reached, which results in running retarded. I've confirmed this by using a timing light. I see the S-mark at idle but I can't see the F-mark in the window when I run the RPMs up to say 3000.

Is this normal? Is there something defective with the advance
unit? I've had it apart for lubrication and all seemed fine. Any
suggestions? Thanks...

Kurt in S.A.