Triple engine uneven idle

[Claviger]

I have long wondered why, regardless of what I do, both of my triples have always had a fairly even idle with the occasional odd "change" in sound/tempo for a split second and then back to solid. It's not something you will notice if you are not nit-picky about your engines, though I suspect most members know what I am talking about.
I figured the best way to reconcile how a 4 cycle engine split at 240 degree intervals causes this a graphical aid would be easiest, so I made the below up to show 3,4, and 6 cylinder motor power stroke events. It is pretty clear to see why 4 cylinders idle rock steady and 6s are just butter smooth.

Mah Chart was fockered up indeed

 

[Wrecka]

So where do i upload those maps to make my bike run smoother ?

 

[Claviger]

Haha Wrecka. I think they are stored in the same bin as the 4th cylinder at Hinckley.
What I don't get though is how despite the gap where no cylinder is on power stroke, the 2014 Daytona 675 is butter smooth, smoother than some 4 pot bikes. I reckon they might have finally learned the magic equation to get the balancing to mask the "missing" power stroke.

 

[Triple Trouble]

I think your chart is flawed. You are also forgetting about balance shafts.

 

[Claviger]

Could be, but I am pretty confident it's not flawed.
Balance shafts are a whole different animal than 4 cycles across a certain number of cylinders, but you are right, in that they can pretty effectively mask the nature of certain motors.

 

[Triple Trouble]

Each cylinder in a four stroke engine fires every 720 degrees regardless of how many cylinders it has. That does not happen in your three cylinder chart nor the six cylinder?

 

[Claviger]

Crank spacing is 240 degrees for a triple and 120 for most 6s. It is mathematically impossible for that crank spacing to be 240/120 and all cylinders to fire every 720 degrees using 4 cycles and 3 cylinders, only engines with multiples of 4 cylinders can do that.
Strange it is, but you cannot divide 720 degrees into 4 cycles and end up with crank spacing of 120/240, it would be a 180 degree triple, something that has been done, but generally runs like doodoo.

This is exactly why I did a chart lol, because it is totally and utterly counter-intuitive to have 3 cylinders across 4 cycles.

 

[Triple Trouble]

Crank spacing on a triple is 120 deg. It will have a powerstroke every 720 deg regardless of crank angle or number of cylinders. You have each cylinder firing every 240 degrees which cannot happen

 

[Triple Trouble]

Crank spacing on a six cylinder will be 120 degrees if it is a straight six. Totally different if it is a v6 with an angle of 90 degrees. Norton twins have a 360 degree crank where the pistons rise and fall together which gives an even firing order but it vibrates because of the weight of the two pistons rising and falling together. Yamaha came out with a twin with a 180 degree crank where the pistons were opposed, 180 degrees apart. This still vibrated because it had an uneven firing event which caused a rocking couple in a different plane than the Norton. There is no simple solution.

 

[Claviger]

A triple is a 240 degree motor as it pertains to the otto cycle, but yes the crank is made by even spacing three 120 degree rod journals. Even if it fired every 120, it would still be uneven, like the 6 cylinder chart. There are differing overlaps, explaining the uneven timbre/idle feel of a triple.
Not trying to argue lol, just trying to un-**** this in my head lulz.

As one reputable source for 240 not 120 figure:
http://www.bmwblog.com/2012/08/11/technical-overview-bmw-3-cylinder/