I have been following another thread on here and it really got me to thinking about just what really is goin on in that metal noise maker below my seat. ( c'mon now! the engine!)


When it comes to the shape of the lobes (get ready for some more un-educated guesswork):

Could it be that the actual timing is taken set to the front cylinder. Therefore , it has to be accurate. The sharp lobe will enhance this Picture that little bugger scootin around 4000 tines a minit. Very quick on/off.

Now the rear cylinder doesn't establish timing. The motor is already spinning and just has to follow the front cylinder.

Any internal combustion engine will fluctuate slightly with a timing light on it. Our bikes have big cams , big valves, solid lifters(too cool) so they tend to lope and fluctuate just a little more.

If a timing light shows the timing mark moving forward and back, this means that the timing is fluctuating just a bit from one time that the front cylinder fires to the next, even with the sharp lobe.

That being said, timing probably also fluctuates from the time the front cylinder fires 'til the rear cylinder fires.

If that is the case, then the shape of the wide lobe WOULD cause a softer spark. Possibly less intense? But possibly longer?

The coil is basically an amplifier/capacitor? It charges, amplifies, then dumps. If that wide lobe causes resistance from the time the contact starts to break until the contact is completely broken, then the coil would be amplifying less than 12 volts. (11v*25,000 is much less than 14.4v*25,000).

Also, if the ramp is more gradual then the dump would be more gradual too, but less intense because the coil has already started discharging before contact is completely broken at the points.

This being the case, a longer softer spark, it would be more forgiving if the timing had in fact fluctuated from the first cylinder fired 'til the second one did.

That way, the two cylinders would be fighting each other less. And seeing as how both connecting rods are hung on the same crank pin, this is a good thing.

CAUTION to anyone reading this!!!!! These are nothing more than thoughts and theories based on a progressive string of ideas. This COULD all be total and utter nonsense!

If anyone has any opinion, be it supportive or not, I think it would be interesting to hear.

 

Awh man, just read a new post and changed my mind. In order for the timing cam to be balanced at high RPM's, it has to weigh the same on both sides 9or at least close to the same). If our pistons were firing 180 degrees from each other , the timing cam could have 2 sharp lobes. But because our pistons fire 90 degrees( which, may I add makes 'em sound badass!) away from each other there has to be 90 degrees from the time the points break once until they break again. If there were two sharp lobes 90 degrees from each other the timing cam would be WAY out of balance and beat the heck out of itself and everything around it. So to counter this, the second lobe is longer, to keep the lobes 180 degrees from each other, but the breaking positions are 90 degrees apart. The cam would still be slightly out of balance but not near as bad as it would be if there were 2 sharp lobes 90 degrees apart.

 

OK just what kind of beer or other stuff are you guys doing ? And I thought I did it all !!!

 

I quit all that stuff years ago. Now my mind wont stop!!!!!!!!!!!!!!!!!!!!!!!!!

 

I want a Piniongear response to this info ! Thank you very much

 

Here is the flow path of electricity through the system:
The initial current comes from the battery.
When the points are closed (which means the contacts are touching and this is a grounded condition), the current flows from the battery through the primary side of the coil to ground and back to the battery.

When the ignition cam opens the points the circuit is broken. This causes a high voltage surge produced in the coil primary side to jump over to the coil secondary side.......down the spark plug wires.......and both spark plugs fire the air gap on each.

Back at the points..... the condenser is connected to the circuit with the breaker points and the condenser functions to produce a quick collapse of the magnetic field in the coil. This sudden collapse is what produces the high voltage in the coil.
The condenser acts to prevent current from continuing to flow across the points after they have opened. Without a condenser the current would continue to flow across and result in early burning of the points contacts

The engine must be timed to fire at the proper place before top dead center of the compression stroke is reached.

The shape of the cam lobes is something we should just take for granted. Just consider their shape an engineering necessity owing to the crank/rod set up in a Harley V-Twin. The cam lobe shapes are fixed, and have nothing to do with ignition timing other than setting the .018 gap right at the high point of that sharp front cylinder lobe.
pg

 

ya, kinda scary to think that I'm gonna be riding this thing that I worked on huh!
Don't mean to beat a dead horse. My brain just got carried away.
Thanks!