Timing advance

[weh8127]

My R 60/2 is setup with a reproduction spark advance and Pentacomm plate. While working on the bike today I checked the timing with a strobe. At idle the S mark is in the window and when the engine revs the F mark comes into view and then passes thru the window and up out of sight, so the spark is advancing too far. I removed the advance unit and it looks fine, no missing or broken springs. There isn't any adjustment on the stop spring that I can see.

Should I retard the timing so the F mark is in the Window at full revs, and not worry about advance at idle? I should note that the bike runs fine and I wouldn't be aware of anything wrong if I hadn't looked.

[schrader7032]

I've never seen one of those Pentacomm plates up close. I recall Duane Ausherman says that device was a solution looking for a problem!!

Certainly, the timing at full advance is most important. The R69S can't really tolerate being too much advanced as it could harm the pistons...the other bikes might tolerate it some. It would be nice to control where the F-mark stops and then see where the idle mark is. If you can't start the bike because it is not too retarded, then that's not going to work.

The original points system has the ability to change the points gap, change the position when the points open, and has a restriction on how much the advance weights can swing out. The Pentacomm systems needs to have all those features as well I would think.

[Tinkertimejeff]

I am not an expert with this stuff but have learned through a limited experience that those pentacomm things can cause problems.
Having said that I have to ask.
Does the bike overheat?
Does the bike sputter and fail to accelerate as it should?
Does the bike run rich and foul spark plugs?
Does the bike run lean and turn the exhaust and spark plugs strange colors?
From the original post it seems the bike runs and performs as it should, so why fix it.

Now to an old quote, "If it ain't broke fix it until it is"

Don't take this as expert advice please, These are simple machines designed for regular maintenance and simple road side repairs.

[DIS295]

The range of some advances exceeds the nominal 30 degrees, some due to wear, some poor quality control. What you describe would indicate the Ltter. I recently installed a reproduction advance and it has a range of approx 34 degrees. I was able to get the full advance where I wanted it, with the idle timing retarded and still be good starting. If you can retard the timing so you're at the F at full advance, and the idle timing is only a few degrees retarded and starts well, You should be fine. If you can't make that work, it may be time to look at ways to bring the range of advance under control.

Too much advance, especially when combined with constant load running, is not good for piston life.

[Seek]

I don't think the Pentacom plate is the culprit. It's all in the advance. They wear out, the pins, the weights, the whole thing rotating on the shaft. And all these small wearpoints combine together.

Like allready mentioned, don't run the bike more advanced then the F point. It's really harsh on the engine. Too much retard at S is not such a problem. But you can also get creative with the machanical advancer. The weights are stopped at some point by a spring. You might be able to bend this spring just enough to limit the advancer.

[vechorik1373]

Because no one ever bothers to clean and lubricate the pivot hole and post that the advance weights are mounted on, the hole in the weights and the shaft of the post wear, and that alone will cause the timing to go past the "F" mark, when revved up.
The simplest cure, if you have the advance with the ? (question mark) shaped limit spring that is screwed to the face plate, is to buy and add a second question mark spring on top of the original one. This will stiffen and strengthen the spring, and you will find that it will stop the advance from going too far at high speed.
Forget attempting to bend the spring to increase the tension. It WILL break when you try it. Double up the spring with a second one, and your R69S (or any of the other models), will not advance too far.

On the late advances, that have the U shaped limit spring, you can do the same thing, and get the same results.

[schrader7032]

Does anyone have a picture of an advance unit installed with a Pentacomm plate? Here's a picture of just the plate:

https://www.flyingtpot.com/pentacomm-points-plate

[hutchinson5234]

I've installed a few of them on my bikes and customers..The unit looks the same as you posted. What's the problem?

You can set the timing spot on with a timing light and long fallen... It takes a couple of minutes with the front cover over and the engine idling.

[schrader7032]

What about the advance mechanism? I've not seen them both together.

[weh8127]

The Pentacomm plate uses the standard advance unit. Its only advantage is the ability to time a running with a light. In my case, I have it and it works, so Ill keep it.

Attached is a picture of my advance unit. I was not going to try to adjust the stop spring for the reason that Vech gives, but after thinking about it I tried anyway. I was surprised (appalled, really) at how easily it bent under finger pressure and how it held that bend. I put it back in and didn't get the timing where I wanted it. When I took it out again I saw that the pressure of the rotating advancer had pushed the stop spring back where it was in the first place. I that no I should replace the whole unit. This is the one Mike Benoit offers https://vintagebeemerparts.com/new-bmw- ... 8-004-113/ . It looks like a better unit. Does anyone have any experience with it?