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R1100R ignition (spark) pulses per revolution?


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I'm trying to set my R1100 idle RPM & need to know how many spark pulses per revolution.. I know one coil sparks both cylinders so set my tac to 1 pulse per rev (it is an inductive unit that reads off of one spark plug).. It shows the idle at about 600 RPM's.. Is it possible that I am getting 2 pulses per rev (it shows 1200 RPM at that setting)..Thanks.....

 

Twisty

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duckbubbles

I am not absolutely certain, but I believe there is one spark event per revolution. One at the end of the compression stroke to ignite the mixture. The next one is near top center of the exhaust stroke, the same time that the other cylinder is firing on compression.

 

Frank

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Thanks Frank,, that is also what I thought (assumed).. If I set my tac to (1) pulse per revolution I get 600 RPM shown at idle.. If I then use the hand throttle & raise the RPM to 1200 it sounds like it is revving way too high.. If I set the tac to (.5) pulses per revolution it reads about 1200 RPM's at idle.. I'm pretty sure the idle is close to correct as it idles pretty good & doesn't stall.. (I just bought the bike so don't know what a proper idle speed sounds like yet)..

 

Correction: I mispoke in the first post --That should read 1 pulse per 2 revs not 2 pulse per 1 revs (sorry)

 

Twisty

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Maybe glance at the tachometer? smile.gif

The Oilheads send one spark to BOTH cylinders every 360 degrees of rotation. Only one is needed for each cylinder and RPM is based on the number of spark events TOTAL. I would think the .5 setting should work. Idle should be about 1,100-1,150 RPM.

 

Mick

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duckbubbles

Twisty, if the engine was trying to idle at 600, I think you'd notice it shaking and laboring, if it would run at that speed at all. I agree-1100 rpm is a good starting point.

 

Frank

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Mick, if it were sparking both cylinders once per 360° that would be 1 pulse per revolution (remember I am only reading off of one plug wire).. If I can believe my current RPM is correct & I have my tac set to .5 pulses per revolution that would either mean I am getting one spark per cylinder per 720° of crank revolution OR I am really idling at 600 RPM's..

I can't find any information, either in my service manual or on-line about the 1100 BMW sparks (pulses) per crank revolution.

This thing has 2 hall effect sensors (at 180°) & the hall effect sensors are on the crankshaft centerline..

You say each cylinder sparks once per 360°, where did you find that information?

I am still confused as this thing either sparks each cylinder every 720° or it is idling at 600 RPM's now..

Both throttle body base idle screws still have the blue paint intact & the air by-pass screws are set at 2-1/4 turns out from seated..

 

Twisty

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Joe Frickin' Friday
You say each cylinder sparks once per 360°, where did you find that information?

 

It's a single ignition coil that services both cylinders; some of us have held that coil in our hands and seen how it's wired, so you can trust the info is accurate. Two spark plugs and one coil are all in series on the same circuit. at the first TDC one cylinder actually combusts, and at the next TDC the other cylinder actually combusts; but both cylinders see a spark on every TDC. So if you hook your spark detector to either plug wire, it's gonna see a spark every time the crankshaft completes a rev.

 

It's possible you really are idling at 600, but it probably is shaking like crazy. Doesn't this bike have a stock tachometer you can look at? confused.gif

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Mick, if it were sparking both cylinders once per 360° that would be 1 pulse per revolution (remember I am only reading off of one plug wire).. If I can believe my current RPM is correct & I have my tac set to .5 pulses per revolution that would either mean I am getting one spark per cylinder per 720° of crank revolution OR I am really idling at 600 RPM's..

I can't find any information, either in my service manual or on-line about the 1100 BMW sparks (pulses) per crank revolution.

This thing has 2 hall effect sensors (at 180°) & the hall effect sensors are on the crankshaft centerline..

You say each cylinder sparks once per 360°, where did you find that information?

I am still confused as this thing either sparks each cylinder every 720° or it is idling at 600 RPM's now..

Both throttle body base idle screws still have the blue paint intact & the air by-pass screws are set at 2-1/4 turns out from seated..

 

Twisty

 

The R1100 engines only use the TDC (Hall I) for the spark event and yes, both plugs fire each TDC. The 180 (Hall II) is used for fuel injector timing. The combination of Hall I and Hall II are used in the Motronic to make a signal called TD. This is a square wave that is used to pulse the injectors.

I read a lot of technical stuff. smile.gif

Based on what you say that timing light does, yes, you are idling at 600 RPM.

 

Mick

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I'm as lost as everyone else on this, should be one spark per rotation but if is idling at 600rpm it would be shaking like a paint shaker. If on level ground you can ease the clutch out and move off slowly without touching the throttle, it isn't idling at 600rpm.

 

As far as all the questions regarding looking at the tach on the bike, the clock and tach were options on the R1100R's so it likely doesn't have a factory tach.

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Mick, that makes good sense.. I do know it has a wasted spark coil system..

OK, I borrowed my neighbors RFI antenna pick-up tac & it verifies my induction tac.. It reads 600 RPM on 1 cyl 2-cycle setting (correct for lost spark systems) OR 1200 RPM's on 1 cyl 4 cycle..

Now to figure out why it is idling so low.. Opening the air bypass screws all the way only gives me about 780 RPM's (no effect after 3 turns out) & the throttle plate base idle settings are still factory..

I pulled the bypass screws & the tips were pretty carboned up so I cleaned them.. I will try to clean the bypass screw seats tomorrow.. Do those 1100's have a problem with the throttle bores & throttle plates cokeing up? Maybe I have a throtle bore cokeing problem as the original owner didn't ride it much (9,500 miles since late 1995)..

It sure doesn't sound real low at idle though..

Would you think the charging light would be on at 600 RPM idle?

 

Thanks...Twisty

 

Twisty

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ShovelStrokeEd

I find it hard to credit that the bike is idling at 600 RPM despite what the tach says. Since I don't know the specfics of the timing light in use, I can't comment on what setting you should use. However, if you (briefly) rev the snot out of it in neutral it should read something up in the 7000 RPM range. If it only reads 3500 or so, you have the wrong setting.

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Ed, I have tried 2 different tacs.. One is an old Snap-On inductive unit that clips over one spark plug wire.. It has a simple setting procedure as you just set the spark pulses per 360° crankshaft rovolution (offerings are .5,1,1.5,2,2.5,3,3.5,4).. Very simple & very accurate & it will work on about anything with a spark..

The other tac is a radio frequency pick up (antenna over a plug wire) & I used it set to (2-cycle & 1 cylinder) two cycle is the setting for a wasted spark ignition system as it sparks every TDC..

I did try revving it but the tac basically swings to mid scale on a quick blip as it takes a while to stabilize..

Twisty

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Ignoring the hand held tachs for a minute, what problem are we trying to fix here? Is the bike actually idling unusually low? I.e. - As someone correctly put it, is it "shaking like a paint shaker"? Which indeed it would at 600 RPM. I'm not sure a boxer engine will even continue to run that low.

 

If it is actually idling too low (does the idle speed sound low?) have the idle stop screws been messed with at any time?

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Joe Frickin' Friday

Two other options for verifying your tach:

 

1. Get a musician to listen while you rev the engine steadily in the middle of its range. When your musician hears a low concert B-flat note, the engine is right close to 3600 RPM (i.e. a 60-Hz pulsetrain), which is what your tach should be reading.

 

2. Get another boxer, with a stock tachometer, and hook your handheld tach to it. Set your tach so it reads whatever the stock tach reads.

 

Where in Michigan are you? I have a boxer with a stock tach (#2), and I also have a pretty good ear (#1). I'd be happy to help out.

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Ken, no real problem, I just bought the bike (used) a week or so ago & have been balancing the throttle bodies, changing fluids, & generally going over the bike for any existing or soon to be problems (bike is in real good shape)..

Well I get to checking the idle RPM & figure it's a wasted spark & spark once per rev per cylinder so set my tac to 1 pulse per rev & proceed to check teh idle speed & it shows 600 RPM's.. Seeing as this is the first Boxer BMW I have owned I really don't have an ear for idle speed yet (I also have a Honda GoldWing & Harley electra glide).. The idle SOUNDS a little low to me but if I hold it to double what my tac shows it sounds high to me (confused yet?)..

 

I guess what my aim here is to figure out what my REAL idle speed is now so I know what my tac is to be set to & what a proper idle speed sounds like..

It does seem to idle decent now but does sound low to my untrained ear..

IF this bike does in fact spark every piston up (that is what is said above from the posters & seems to make sense) then it (is) idling at 600 RPM now..

 

Twisty

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Since you say the throttle stops still have the blue paint intact, I would verify the TPS voltage (.380V when measuring between pins 1&4 on the TPS connector Ignition on, engine off)

The TPS has a large effect on the idle speed. The TPS should also have blue paint sealing the screws.

I would also verify the timing is correct. Retarded timing can also affect the idle speed. With a timing light you should see the "S" lined up in the timing window (remove the timing mark access plug above the right throttle body). They bike is static timed at "OT" (TDC) and the Motronics advances it to 6 degrees BTDC at idle which is the "S" mark.

 

Mick

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Mick, my TPS is set to .385v (on base idle stop) so that is good to go.. That's a good idea on the ign timing.. I was going to eventually verify that anyhow but will move that up to the top of the list..

I also think I am going to try & slow it down some with the air by-pass screws.. My thinking is if I can slow it down a few hundred RPM's then it ISN'T idling at 600 RPM now.. If I can't lower it a few hundred then it is probably already too low..

 

Twisty

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Joe, Im in the Brighton area.. If we're close I would like to take you up on your listening offer.. I wonder if you could tell over the phone as it has a distinct putter sound to it at idle.

 

Twisty

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I don't know why your tach settings don't work, but I'm willing to bet good money that you're idling at 1200. With the TPS voltage correct, 1000-1500 would be about the range of adjustment available with the bypass screws. I'm still trying to think of a way to get a 600rpm idle with the sealed stops and correct TPS voltage.

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Davis, I have been wondering that myself.. The only theroy's I can come up with is the tac is only seeing the spark on the compression stroke due to a higher KV to ovecome compression & mixture on compression ( a real long shot on that one)..

OR, the by-pass & throttle plate area is coked up enough to restrict air flow..

 

Twisty

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Given that, I'm betting you're fine. Again, at 600 RPM a boxer would barely be able to keep running, if at all. It would be virtually shaking itself off its stand.

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Joe Frickin' Friday
Joe, Im in the Brighton area.. If we're close I would like to take you up on your listening offer.. I wonder if you could tell over the phone as it has a distinct putter sound to it at idle.

 

Twisty

 

Check your PM for my phone number. I'm betting you're idling closer to 1200 than 600, but I'll be happy to check it out for ya.

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I'm trying to set my R1100 idle RPM & need to know how many spark pulses per revolution.. I know one coil sparks both cylinders so set my tac to 1 pulse per rev (it is an inductive unit that reads off of one spark plug).. It shows the idle at about 600 RPM's.. Is it possible that I am getting 2 pulses per rev (it shows 1200 RPM at that setting)..Thanks.....

 

Twisty

 

Here is the deal…

 

Your boxer (mine too) is a four stroke engine with two cylinders, each one requiring a spark every other trip by the pistons to TDC.

 

Your boxer ignition is a wasted spark system and therefore, both plugs receive a spark every trip to TDC. Of course, with the exhaust valve open, no combustion occurs on the exhaust stroke cylinder even though the spark is there.

 

So, set your instrument to read each pulse so that the spark occurrences are multiplied by two and you should read actual engine RPM.

 

In reality, the boxer ignition system is performing as if the engine were a two stroke. Therefore, it fooled you.

 

Your idle RPM appears to be within spec if the measurements are taken at hot engine.

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DEF, if you read back through the threads here you will see my tac doesn't care how many cylinders or what cycle the engine is.. It is strictly a pulses per rev type induction tac.. It clips to one plug wire (one side ONLY) & you set the tac input pulses to how many sparks per revolution that particular plug wire sees per revolution.. In the case of the BMW 1100 it seems to be one pulse (one spark) per 360° crankshaft revolution.. So I set the tac to (1) pulse per rev.. Problem is that shows it is idling at 600 RPM.. If I set the tac to (.5 ) pulses per revolution (that would equate to one pulse per every 720° of crankshaft revolution) it reads 1200 RPM..

 

OK to add a little more data from my side of the fence—Last night I bottomed out the air by-pass screws & it dropped the idle RPM to about 400 RPM’s (on my tac) .. It idles smooth as a Honda at that setting so that was enough to convince me that it is in fact idling at 1200 RPM when my tac shows 600 RPM’s..

 

I still can’t understand why though.. My tac is set to ONE spark pulse per crankshaft revolution & hooked to one side ONLY plug wire but shows ½ engine speed.. I even borrowed my neighbors antenna input tac (reads spark pulses through an antenna wand) & with it set to 2-CYCLE & one cylinder it reads the same as my tac. .If I set that RFI tac to 4-CYCLE it reads 1200 RPM..

 

For some reason both my induction tac & my neighbors RFI tac both only read every other spark going to a cylinder.. Maybe it has to do with the wasted spark system & the KV difference between a compressed cylinder & a cylinder on the top of exhaust stroke,, or who knows..

 

I am pretty well convinced that it is in fact idling at 1200 RPM so I would like to thank everyone for their help here.. If & when I determine why both the tac’s I used work incorrectly on the BMW system I will post a follow up here..

 

Twisty

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  • 2 weeks later...
Shawnee Bill

I also do not have a tach on my bike, same bike I think, I worried some about the idle speed at first. It sounded about right, it idled fairly smooth. I have now listened to many other oilheads idle and figure mine is about right.

 

You should take Mitch's offer, ride it over to where he is and let him take a look and listen.

 

I also bought mine used, 3 years ago it was 8 years old and only 5500 miles, thanks to the evil influence thumbsup.gif of this forum it now has 84,000 miles clap.gif

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