Topic: Dwell angle

[jmd10259]

Does anyone know the correct dwell angle for each set of points? I have e a meter I used all the time way back when, but forget the correct number I'm looking for thanks. 77 750f2

[Deltarider]

It will be 23^o - 24,5^o when measured in degrees on a 8 cylinder scale, which corresponds with a 0,4 - 0,3mm gap. When measured in % Duty Cycle, it needs to be within 51,1 - 54,4%.

[Nurse Julie]

Depends on how worn the points are. The gap on one of my bikes is set at just over 0.2 these days on a set of 45 year old points 😁😁

[TwoTired]

The dwell angle is the period of time where the points are closed during the rotation of the points cam.  This is the coil energy charge time per revolution of the crank.

I believe the actual spec is something like 190 degrees of rotation.  Which you can measure with meters that are designed for or calibrated 2 cycle motors (fires once per revolution).

Other dwell meters "interpret" the dwell angle by electrical trickery, integrating on/off times and inputting that to a meter movement.  There is often a switch that alters the output to reflect a 4/6 or 8 cylinder engine.  None of these apply directly to our 4 cylinder wasted spark ignition systems.  But, they can still be useful, if you calibrate the one you have for SOHC4 use.

With a new set of points set for .016 in gap, attach the meter, and look at what is displayed.  Record or note what this is.  Later when the points are worn irregularly or pitted, the dwell meter will allow you to reset the points to the same actual gap that a feeler gauge can no longer measure accurately.

The problem with using dwell meters, is the movement of the points mounting plate in the engine mount bosses.  When the screws are tight, the plate won't shift about.  But, when you try to adjust dwell on a running motor, you must loosen the screws.  Then the point springs reacting to the rotating points cam push the plate about in the bosses.  This alters the point gap and dwell of both point sets while the motor is running, making it a game of when the screws are tightens during the rotation the determining factor for the finished dwell setting.  And, sometimes making the 2-3 setting impossible to achieve proper dwell or altering the final timing timing beyond the range of adjustability.  A points plate to has .005' lateral movement can allow the point gap to vary that much, too, and firing point to move at least that much when the plate is not screwed down tight.

Yes, the timing light and dwell meter can result in a nice accurate setting.  But, not unless the timing plate is fit (or shimmed) with no lateral movement tolerance, when the point springs are defeated from contact pressure on the point cam.  Otherwise the 1-4 setting will "float about" during dwell or timing adjustment on a running engine.

FYI.

[scottly]

The problem with using dwell meters, is the movement of the points mounting plate in the engine mount bosses.  When the screws are tight, the plate won't shift about.  But, when you try to adjust dwell on a running motor, you must loosen the screws.  Then the point springs reacting to the rotating points cam push the plate about in the bosses.  This alters the point gap and dwell of both point sets while the motor is running, making it a game of when the screws are tightens during the rotation the determining factor for the finished dwell setting.

In my experience it is better to only measure timing and/or dwell with the screws snugged down before running the engine. If adjustment is needed, shut the engine off, make an educated guess on the adjustment, and re-test. Repeat as necessary.

[Deltarider]

In my experience it is better to only measure timing and/or dwell with the screws snugged down before running the engine. If adjustment is needed, shut the engine off, make an educated guess on the adjustment, and re-test. Repeat as necessary.

As a matter of fact, this is what I suggested on the UK forum, just five minutes ago.

Ignition always comes first in diagnosing. No matter what ignition you have, concentrate on a correct timing at full advance. I like mine to be just a tad more advanced than the outer mark. Then just accept the timing @ idle it will result in and live with it. Although I recommend using a strobe timing light, I myself don't do the actual adjusting dynamically. I set and then check using the timing light. If I need to readust, I first kill the engine, do an extra adjustment and check again. If necessary, I repeat this. This works best.

Same goes for setting the dwell, although this I sometimes do with the engine running.
Important is to start with readjusting the breakerpoints. When one would have practised this from when the bike was new, you would have learned you never ever have to adjust the timing plates.
That's the problem with manuals: they have to describe every possible job. Owners who never did the maintenance themselves, but preferred to have this done at a Honda dealer, probably never knew that these mecs always did the timing by simply readjusting the breakerpoints and never moved the plates. When the range of readjustment proved not enough anymore, it was time to renew the breakerpoints. But the plates were left untouched.

[Keith]

The problem with setting the point gap to adjust timing is that the dwell setting is changed. So, with a high dwell reading, the points are closed for a very short time and open for a very long time. The coils are energized while  the points are closed, the plug fires when the points are open. So this affects the kv available to fire the plug.

[Keith]

You are correct however, the dealer mechanic was just resetting the dwell to its original setting.

[Deltarider]

Sorry to correct you. The higher the dwell, the narrower the gap, the longer the coils are 'on'.
Practically all off timing has its origin in wear of the breakerpoints. So if you bring the dwell back to where it was, also the timing is correct again. There's no reason to fear the three big crossheads loose their grip on the plate ever.

[Keith]

You are correct. Completely closed points will read 90 degrees. Adjusted too far open will be a weak spark.

[Little_Phil]

Be interesting to know what the dwell variation is between 0.3 and 0.4mm. Presume the rotational dwell of 190deg is at 0.35mm. As said dwell is to allow for enough  time to adequately saturate coil which will be shortest at max rpm.

[Deltarider]

[...] As said dwell is to allow for enough  time to adequately saturate coil which will be shortest at max rpm.

I wouldn't worry anout that. Usually mecs would set them gapped at 0,4 - 0,35, calculating over time gap would decrease.

[Lars]

It will be 23^o - 24,5^o when measured in degrees on a 8 cylinder scale, which corresponds with a 0,4 - 0,3mm gap. When measured in % Duty Cycle, it needs to be within 51,1 - 54,4%.

So, you simply devide the favtory given dwell angel which is 190 for a CB550, on number of cylinders which is 4, which gives 47,5 degrees? That is 23,75 if you use 8 cylinder reading.

[MauiK3]

I’ve tried a dwell meter but now I stick with feeler gauges, simpler.

[HondaMan]

I’ve tried a dwell meter but now I stick with feeler gauges, simpler.

...and more accurate for setting the timing...

[Deltarider]

I don't agree. (Re)setting gaps using feeler gauges is fine and if you don't have one, there's no need to buy a dwellmeter. But a dwellmeter can detect a rotten cam and/or misaligned breakerpoints. It's my habit in the beginning of every riding season, to connect an automotive multimeter. With that meter in the tankbag I make a ride and check for both ignitions if dwell angle stays the same all the way into red zone. It always did. That's why I said you don't need to buy one. But if you have one, I'd use it. Working on older cars of friends I've detected some 'fluttering'.

[dave500]

just put an electronic unit and be done with it?#$%* points man,#$%*ing flintstone age?

[TwoTired]

just put an electronic unit and be done with it?#$%* points man,#$%*ing flintstone age?

Which ones allow keeping the stock dwell angle?

  That’s the coil charge saturation time.  The Dyna almost doubles that time, stealing unnecessary power from the charge system.

But, I gotta ask: Why are you riding a bike from the flintstone Age?  Shouldn’t you have a more modern one?  #$%* old bikes, right? :-)

[MauiK3]

I know electronic systems are superior to points, that being said, I made two US coast to coast trips back in the day on my 750 K0, one of them was 10,000 miles. I also made some long trips on my 75 GL1000.
During these trips I never touched the ignition at all. I had chain issues and always had a spare, I had a flat tire once, I had a sore butt and numb hands, but I never cracked the points covers. One of the trips was with another K0, one was with two other K0's and one Suzuki Titan 500. No points issues.
Condensers must have been a lot better back then.

[Tracksnblades1]

I know electronic systems are superior to points, that being said, I made two US coast to coast trips back in the day on my 750 K0, one of them was 10,000 miles. I also made some long trips on my 75 GL1000.
During these trips I never touched the ignition at all. I had chain issues and always had a spare, I had a flat tire once, I had a sore butt and numb hands, but I never cracked the points covers. One of the trips was with another K0, one was with two other K0's and one Suzuki Titan 500. No points issues.
Condensers must have been a lot better back then.

How many times did you change the oil on the 10,000 mile trip..?
Back in the SD/SE oil days…

[PeWe]

This thread Mike started made me to jump on the dwell train!
http://forums.sohc4.net/index.php?topic=147444.0

Easier to get points right and equal, adjusting them while engine is running.
Dwell meter will show how to adjust, your ears will hear the result of an even running engine.

I have later on changed to Dyna-S. Easier and quicker to adjust.

I have seen change in charging with Dyna-S. My bikes have volt meters between the gauges to look at while riding.
Strange voltage drop after 5000rpm compared with points. Charging still OK.

[Don R]

 Speaking of ignition electrical load, I accidentally rode my Gerex ignition equipped 836 with no charging system. The red/white feed wire was unplugged.
  When the battery went down there was a distinct power difference above 3,000 rpm. It was like someone flipped a switch and the engine came to life. Below 3K it barely ran.
  I assume that is the rpm when the Gerex stopped multi-sparking, the watt load lessened, and why, when I failed to keep the revs up, it died at a stop sign. I gave the battery a rest, turned on only the led parking lamp, kicked it to a start and kept it revved up all the way home. Would have been a good time to have the ARD magneto on it. lol.

[HondaMan]

Speaking of ignition electrical load, I accidentally rode my Gerex ignition equipped 836 with no charging system. The red/white feed wire was unplugged.
  When the battery went down there was a distinct power difference above 3,000 rpm. It was like someone flipped a switch and the engine came to life. Below 3K it barely ran.
  I assume that is the rpm when the Gerex stopped multi-sparking, the watt load lessened, and why, when I failed to keep the revs up, it died at a stop sign. I gave the battery a rest, turned on only the led parking lamp, kicked it to a start and kept it revved up all the way home. Would have been a good time to have the ARD magneto on it. lol.

Did the multi-sparking RPM range help keep the plugs cleaner?