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Discussion Starter #1
Does the timing look correctly adjusted? (I can't start the bike to test at the moment -- only half filled with oil.)
The threshold between where the points open and close -- when the light turns on -- is very close if not exactly where the F mark meets the indicator mark (in the video at 0:12 and 0:22).
But I'm not sure why the points close again approx 2/3 of the way around, as opposed to at the exact halfway point from the indicator mark or after a full rotation.
The points are brand new and the gap is .012.

 

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Depends on how you have the "timing indicator" light connected.....And how/where you set the gap.....

I'm assuming you have the alligator clip from that light connected to either the point wire attachment bolt or the point spring.....

The light then comes on when the point opens and removes the intervening "short to ground" and completes the circuit through the bulb to ground....

The points close before reaching the full revolution to give the coils time to "charge", commonly referred to as "DWELL"...
The duration of the dwell (in degrees) is pre-determined by the shape of the breaker cam and the Gap, so the only critical things you need worry about are Gapped correctly (.012" to .016" (I set mine at .014") and that the light comes on EXACTLY at the "F" line/index line alignment......
 

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Discussion Starter #3
Thanks so much for the reply. Yes, the alligator clip is connected to the point wire attachment bolt. I'd heard the term "dwell" around but wasn't sure of its meaning -- thanks for that. It looks to me like the revolution that completes at 0:12 in the video shows slightly retarded timing, very slightly, but the next revolution, that completes at 0:22, is exact. I may be seeing things, but I found that this was repeatable. Slightly off, exact, and so on. I'm not sure if there's any significance to that or if something different is happening "every other revolution" vs every revolution.
 

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Your breaker cam has two lobes that MAY vary slightly...... Most techs "average" the error......
Remember, the camshaft only turns 1/2 a rotation for every 1 full crank rotation...So, each crank rotation shows the resultant action of a different one of the two lobes....

And the Dwell might seem long when you are turning the crank by hand, but it's actually quite brief in operation.....

Don't forget the couple drops of 90 wt oil on the felt cam lube pad......
 

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Discussion Starter #5
Ah, variation in the lobes of the cam! "Averaging" the difference makes perfect sense. I am keeping that pad in mind -- it looks a bit worn down and seems to barely be contacting the cam any more. Will try to adjust into better position and, indeed, add that oil.
 

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I have a Charlies Place electronic ignition on one of my engines. This retains the stock advance retard mechanism, but obviously does not use the points cam.

In the fitting instructions it states:

.On all 160/175/200 parallel twins it is necessary to rotate the crankshaft two full revolutions in order to correctly check the timing for both cylinders. Often it is necessary to “average” the two readings, or find a setting that allows the closest timing on both cylinders. Our magnets (on the rotor) are exactly 180 degrees from each other. However, the cam chain is rarely an even length on both sides.
 

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I'm the same, Charlies on one machine and Points on the other. I have to "average" out two readings. Indulge me here, I might be mechanically incorrect so please put me right if I'm wrong. By averaging out the two readings, I'm assuming that the spark will fire slightly later than it should on one cylinder and slightly early on the other. Does this mean the early one is getting ignited while the piston is still rising? If it is, I've wondered if it would be best to have one cylinder bang on and the other late, igniting it on it's downward stroke and pushing it along in the direction it's already going. I'm guessing 'F' is designed to be slightly later than TDC but what if averaging puts F too close to TDC? Perhaps the difference between the two is much more than any "averaging" could possibly influence, I don't know.

EDIT : I'm wrong here. Reading up on it, optimum spark happens before TDC, the above video should have told me that. ;) So averaging will still have one cylinder firing a little earlier than it should, but still before TDC.
 

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The spark should ALWAYS occur while the piston is still rising on the compression stroke...... The amount of rotational time before TDC is the number of degrees of advance...
The spark ignites the fuel/air mixture, BUT like any fire, the flame front requires a certain amount of time to spread throughout the volume of the dome and generate enough heat to initiate the explosion that pushes the piston downwards......Ideally, this explosion will occur at the exact moment the piston is at TDC and CAN reverse direction... The reason the amount of advance (degrees) increases as the engine revs higher is the flame front needs a "longer head start" to arrive and complete the initial heating before detonation (hopefully staying simultaneous) with the now faster traveling piston as it arrives at that TDC positioning....


P.S. Only the number of teeth on the cam and crank sprockets controls the relative rotational speeds which should be exactly 2:1...
Chain length differential front and rear has nothing to do with it.........
 

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P.S. Only the number of teeth on the cam and crank sprockets controls the relative rotational speeds which should be exactly 2:1...
Chain length has nothing to do with it.........
Without wishing to be overly argumentative, in that case why do we see a variation when Charlies Place rotor is fitted in place of the points cam ? He assures us that magnets are placed 180 degrees apart, so apart from his assertion that it is due to uneven ( wear ? ) lengths of cam chain, what else could cause this ?
 

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Look at this with logic..... the ONLY chain length that matters (assuming the chain is tensioned enough not to go slack between, whip, or "skip" any sprocket teeth) is the length of chain being pulled BY the crankshaft and pulling ON the camshaft to rotate it....That length ALWAYS remains the same (same distance, number of pins/ equivalent full links involved)...So unless just SOME of the camchain is well worn and other sections of it are not as worn ...(I guess it's possible, but pretty unlikely... wouldn't you agree?) that leaves nothing but design or manufacturing discrepancies in the CP ignition to blame for ignition timing errors....
Suppose what would happen IF the slots that "keyed" the rotor onto the advance are too wide or otherwise fit poorly...Or the hole is bored a few thousandths off true center..... Remember, Honda used SEVERAL parts suppliers for the advance units (Hitachi, Nippon Denso, DaiIchi, TEC, etc) and individual but "equivalent/same" parts of those are not interchangeable brand to another brand..... That's why Honda only sold replacement advancers as complete units.....

On the other hand, were you to install a new camchain and the errors disappeared, I would say that would prove the CP assertion.......

I've been wrong before.......
 

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Thanks for that. I had not considered the actual fit of the CP rotor onto the original advance mechanism.

Regarding the cam chain wear, I assume that they are manufactured in a similar way and materials to final drive chains, and we all know how those develop tight spots as they age and wear, and how we are advised to always adjust the chain to give correct free play at the tightest spot. Which means that at the loosest spots the chain is effectively longer, due to wear.
 

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Ahhh.... But drive chains are not almost continuously dipped, splashed, dunked/bathed in oil...... Cam chains are......

The tightest area (pull area) between crankshaft and cam or cams is all one has to consider when discussing the timing.....

The "slacker" side is where the tensioner has effect, (theoretically eliminating/drastically reducing the slack), and the chain could be much longer if properly guided and tensioned.... Case in point, the DOHC 450...... ;)

002_zpsslnqokuv.jpg
 

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22 links on the tensioned front run of that chain (give or take). Thats 44 pins and bushes. I'm going with slight variations in wear on the chain, seems the most likely culprit and.... something I had never thought of before. Even after all these years you live and learn, or at least have another variable to program in.
 

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Chain is 82 links long...it only rotates 30 (crankshaft) links between repeated firings of the same cylinder (crank sprocket has 15 teeth/cam has 30 on the 175)....
Since neither 15 nor 30 is evenly divisible into 82, you would be at a different area of the chain at each point firing or at each TDC......
Honda engineered this to eliminate uneven stressing and thus uneven wear on the chain....
No doubt that there is eventually some chain and sprocket wear, but, a theory that requires that SOME areas/lengths of the chain are worn significantly more than others is foolish considering the above .....

PLEASE provide an explanation for point timing repeat-ability assuming your suggested theory about chain wear/"stretch" differential were true......
 

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Apologies for going well off original topic now, but in another forum I read that a badly ( but evenly ! ) worn cam chain would affect the cam timing. I'm still trying to understand if that is true or not.
 

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To me, a badly worn chain could result in inaccurate timing either if the tensioner could no longer adjust enough to keep it fully tight, resulting in erratic cam movement when valves are opening and/or closing, or just the amount of lag in the movement of the cam as compared to the crankshaft due to overall chain stretch. Seems to me that would be an extreme situation and could result in a lot worse depending on just how sloppy the chain was
 

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I'm with Steve on this.
If the tooth on the crank is pulling the corresponding cam tooth then the distance between the two are immaterial and so is the chain length ( worn or not). This is how the derailluer on a bicycle works, or the belts in a drill press.
Since the chain is an irregular length ( relative to sprocket teeth) it can't be worn in a section to produce a repeatable left cylinder is correct right cylinder out condition. Both cylinders timing would shift as the stretched section came in contact with the sprocket.
If chain stretch were to affect the timing it wouldn't/couldn't only affect one side of the engine in a repeating (ever 2nd fire) manner
 

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Do timing chains "stretch" and sprockets wear?....YES....
Does this cause Crank to cam lag?...YES, eventually they can wear to the point it becomes problematic...
(But hopefully the camchain was checked and replaced with new as necessary during each re-ringing/overbore to minimize the effect)....
Can the chain wear/("stretch") affect the timing ONLY SOME of the time.... I'll have to stick with a resounding NO!....
Not saying it absolutely isn't possible, just in fifty-odd years I've never seen it happen.....


YES, we have wandered far from the original poster's needs....Fortunately, I believe we had him answered within the first 4 replies.....:D;);)
 

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Simo wrote:

Since the chain is an irregular length ( relative to sprocket teeth) it can't be worn in a section to produce a repeatable left cylinder is correct right cylinder out condition. Both cylinders timing would shift as the stretched section came in contact with the sprocket.
If chain stretch were to affect the timing it wouldn't/couldn't only affect one side of the engine in a repeating (ever 2nd fire) manner
Yes, of course, all is clear now, completely blows the worn cam chain theory out of the water.

As a further aside, with an 82 link chain running on 15/30 sprockets, how many revolutions of the crank would take place before an individual chain link arrived back at the same position on the two sprockets. The maths defeats me ….
 

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I'm sure there is an equation for that, but I'm also sure it's not a simple one... I think the moral of the story is "replace your cam chain while the engine is down", and for the other guy "don't try to out-do Honda by using double points on your 360° crankshaft engine" :lol:
 
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