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Old 12-24-2012, 07:54 AM   #1
Captdan OP
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R90/6 timing

In my education of the r90 it seems I've run into a timing issue. I read my shop manual, did a static "s" time with a test light and she ran really bad. I read the thead on timing. What I wound up doing was adjusting the timing plate until the bike ran good. But, when checked with a timing light found the "f" in the window and not the "s". I checked my fly wheel for tdc and all is well. While the bike ran good, she didn't crank good. So, I went back in and retarded the timing plate. Bike cranks good, and runs fine, however, when using the timing light "s" is still not in the window. When I rev the bike up "f" does appear.

How important is it to have the "s" located in the window? The bike presently runs fine... My idea is to leave well enough alone. .?
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Old 12-24-2012, 08:08 AM   #2
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It is important to have the S or one of the lines on either side of it to line up with the marker. That sets the static timing, before the advance kicks in on acceleration etc.

If you take the plugs out, hook up the timing light and then slowly rotate the engine and see when the light flashes in relation to the marks. You often have to play with both the point gap & the plate to get the timing set right. There is also some slight difference in which mark on either side of the S that you should use, but I don't have my manual in front of me. Others may chime in soon.

Always set the point gap at its widest recommended setting if you can. The rub block wears over time and then the points will close up resulting in backfire and poor driving.
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Old 12-24-2012, 08:20 AM   #3
disston
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The F mark is more important. It appears when the engine and the advance have reached maximum advance at about 2500 rpm. The S mark is for idle and should disappear around 1100-1300 rpm.

(somebody else's flywheel)



That is also a lightened flywheel. And white paint has been rubbed into the marks.

Sounds like you either have a worn advance unit or it has been customized for racing and/or performance. It was popular (may still be popular) years ago to restrict the movement allowed by the advance unit. Making it not advance as much as it was intended too. When in use the customized advance unit would run at more advance during idle but stop at the same place it used to. The effect is supposed to be a faster rise. Custom advance curves are an old trick of Hot Rodders and performance geeks.

It is done by various methods. The most common is to braze some brazing rod into the holes of the advance unit where the pins that the springs attach to are. Then the smaller hole is more restrictive.

Look for the copper colored brazing compound on the top of the advance unit. It can be done with welding rod also, so no copper color. And to a small extent by peening the metal around the holes.

Check your advance springs. It's possible the only problem you have is stretched advance springs. You'll be surpprised how much those little buggers cost.
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Old 12-24-2012, 09:18 AM   #4
Captdan OP
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Well, I spoke too soon. The bike starts easy now, but when running through the gears she sputters at midrange then clears out at higher rpm.
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Old 12-24-2012, 09:34 AM   #5
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Just a quick thought, Having the F mark in the window at full advance is the most important adjustment. BMW changed advance units and cams several times over the years. Depending on if your setup is all original or a mismatched mix of parts can throw the static timing off by a bunch. (according to Snowbum)
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Old 12-24-2012, 10:52 AM   #6
Captdan OP
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I closed the gap a bit and it seems to run fine and crank well now....?
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Old 12-24-2012, 10:57 AM   #7
Captdan OP
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Originally Posted by Big Bamboo View Post
Just a quick thought, Having the F mark in the window at full advance is the most important adjustment. BMW changed advance units and cams several times over the years. Depending on if your setup is all original or a mismatched mix of parts can throw the static timing off by a bunch. (according to Snowbum)
I would take stock in that comment for sure. Not really sure if the parts are Stock or not. I don't see any weld marks on the advance so I assume it's stock, the springs and cams seem to be in good shape and spring back quickly. I just did another test down the roadway and she runs like a bat. Also starts easy. So, at this point I'm not going to fool with it.

As I said in another post, without this web site and those like it people like me that need info would be hard pressed to gain info. Thanks to you all.
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Old 12-24-2012, 11:56 AM   #8
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The bill's in the mail... (just kidding) Glad you've got it sorted out! Just out of curiosity, did you notice what the last three numbers are on the advance unit? Can be 005, 007, 010 or 012
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Old 12-24-2012, 01:15 PM   #9
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Originally Posted by Big Bamboo View Post
The bill's in the mail... (just kidding) Glad you've got it sorted out! Just out of curiosity, did you notice what the last three numbers are on the advance unit? Can be 005, 007, 010 or 012

I did not notice any numbers, I'm sure I'll be in there again. What would the numbers mean?
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Old 12-24-2012, 01:30 PM   #10
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Quote:
I closed the gap a bit and it seems to run fine and crank well now....?
Randome twiddling sometimes works but is inconsistent. SET the point gap to 0.016" then SET the timing dynamically using the F-mark. IF the timing at or near idle is still off, find out why. You may need a new advance unit.

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Old 12-24-2012, 01:48 PM   #11
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The F mark is more important IF you HAVE to choose because most all riding is above 3000rpm. If you don't have to make that choice they both are important. Lots of advances need to be fine tuned in order to get the advance curve to spec. Single plugged, I think they run best timed to spec IF they don't ping too much.

Advances are modified for just the opposite reasons disston reports. The modified advances are to have stock timing on the S mark at idle and then have the full advance come up short of the F mark for a retarded full advance compared to stock. It is still a very popular modification for dual plugged bikes because they run so much better thusly timed. Advancing her until she pings and backing it back off just a bit has never really been the road to best power. Now drag racers use curves that retard advance at the end of the run for more power for what a lot of tuners call heat saturation. When the engine is good and hot at the end of the run, it will make more power with the advance retarded from where it was making best power before it got up to full operating temp.
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Old 12-24-2012, 01:50 PM   #12
disston
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These are Bosch numbers and not BMW part numbers. For more info refer to the Tech Pages of Mr. Snowbum as it is way too much info to reproduce here; http://bmwmotorcycletech.info/ignitionsingleplug.htm

The bottom line is avoid the 005 unit unless it is some concurs /5 bike you want and the best of the lot may be the 012 unit or it may not. Any of them other than the 005 will work.

Sometimes you see the numbers scratched off and a new number etched. What that's about I don't know.

There are several issues about the advance unit you will learn about. Light oil or grease on the cam spindle so the advance unit rotates easily and a dab of special heavy grease on the points cam so the rubbing block lasts longer.

Be very careful with the small nut holding the advance unit on the tip of the cam. It is very easy to break. It does not need to be tight at all. 1/16 turn beyond finger tight.
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Old 12-24-2012, 01:56 PM   #13
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I was not talking about dual plugged or modern theories but the way it used to be done and older theories. Anyway it's just the way I remember it doesn't mean I got it right either.

People modify the advance unit. Stock almost always works better.
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Old 12-24-2012, 02:34 PM   #14
Captdan OP
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Quote:
Originally Posted by Bill Harris View Post
Randome twiddling sometimes works but is inconsistent. SET the point gap to 0.016" then SET the timing dynamically using the F-mark. IF the timing at or near idle is still off, find out why. You may need a new advance unit.

--Bill
Well, I guess that's what confused me first. I though I was tying to get "s" in the windows at idle. So, we are saying it's ok to see the "f" mark at idle? Presently I'm between "f and "s" at idle and at "f" reved up. bike starts fine and runs fine. I do detect some popping when the throttle is closed on deceleration. But nothing I can't live with.
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Old 12-24-2012, 02:44 PM   #15
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Quote:
Originally Posted by disston View Post
I was not talking about dual plugged or modern theories but the way it used to be done and older theories. Anyway it's just the way I remember it doesn't mean I got it right either.

People modify the advance unit. Stock almost always works better.
IF your single plugged!
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