2 coils, 4 cylinders wasted spark

[ovlovder]

So, it seems 2 coils with four cylinders is common.

Do they just each fire both plug, ie, is there a wasted spark everytime a coil fires?

[r_outsider]

One coil fires two cylinders at once on a typical motorcycle I-4 with a 180 degree crank, basically giving one big power pulse with every 360 degrees of crankshaft rotation. The only exception I can think of (in production model inline 4 cylinders) is the new R1 with its 90 degree crossplane crank, which fires one cylinder every 180. Which way is better has been the source of much violence and bloodshed amongst engineers, mechanics and bench racers alike, and that's before the various V engine crowd gets into the fray, not to mention those weird "Triple" people.

[Benjamin]

Wasted spark NOT two cylinders at once. The old TZ700 two-strokes fired two and two.

So the wasted spark ends up sparking the almost expended exhaust in one of the cylinders while the other fires. I imagine this is only on pairs that are on the same throw, else you could be sparking every 180 degrees on all cylinders. Either way I don't think it is an issue. If you're chasing more performance then more powerful coils will help, in which case you need four of these. I think halving the coils is a cost cutting measure, the output will still be good enough for the intended purpose.

By the way, typical flat-plane inline 4 fires one cylinder every 180 degrees. The new R1 fires 270-180-90-180 (270-450-540-720) through the two revolutions necessary for a four stroke 4. Almost the same as some 90 degree Honda V4s (can't remember whether it was the 180deg or 360 deg cranks).

Triples are nearly always 120 degrees apart and dead simple. The only engine nicer than a triple is a six. I love triples!

[Chris H]

The Bandit4 fires 1-2-4-3 over 180 deg so wasted spark. one for the compression and the wasted as the exhaust goes over. Some people are fitting stick coils from the later bikes. Ive heard good stories about the quicker dwell of the stick coil, but also some people say they are more prone to over heating because of the wasted spark.

[r_outsider]

Ah, you guys are right. How it doesn't turn into a huge misfire is a little beyond my little brain though.

[Vlad]

How it doesn't turn into a huge misfire is a little beyond my little brain though.

Simple. The other spark happens at the end of the exhaust stroke, so it has nothing to (mis)fire. I would rather call it redundant than "wasted" as the latter implies something undesirable.

[r_outsider]

You know, I really do (or did) know all this stuff. Somehow over the last little while, all my theoretical and most of my practical knowledge of 4 stroke engines has taken a dump. I can't explain it, I don't know why, but apparently I need to engage my brain once in a while and reread everything on this stuff. I've seen the freaking cams, I know the f$%@ing order. I somehow just forgot and filled in the blanks.
I also know that there likely wouldn't be enough unspent fuel at the end of the exhaust stroke to cause a misfire or anything else, as opposed to a two stroker, where there'd be enough left to send a flame out the tailpipe with a late spark (well, it probably wouldn't send a flame out, but it probably wouldn't help matters to have the pressure wave coming back from the expansion chamber still burning (and hence expanding at a faster rate than normal as well as being on fire) just as the fresh fuel charge entered the cylinder from the intake port....err..or something).

Anyway, apologies for the idiocy and thanks for the re-education.

[Chris H]

He,he,he, I love two strokes!!! so easy to work on. Took the B4 for a MOT this week and thers a guy there with my old RGV250 and i was like its Knackerd- who the F.. did that to it! Such a shame to see a bike you put time into get trashed. Going to go with the stick coils in the next week or so, will post any positives.

[Vlad]

Anyway, apologies for the idiocy and thanks for the re-education.

No worries, I learn or re-learn something every day. Speaking of education, what the beep is a "stick coil"? My stock ignition coils already look like sticks, kind of...

[Chris H]

The newer bikes run what are called stick coils as the HT coil is in the actuall plug cap, so getting rid of the bulky HT coil and Ht leads.

[Vlad]

I'm afraid I still don't get it. When it comes to technology it doesn't get much older than the Bandit. It has two frame mounted coils that supply spark to two cylinders each through a high voltage cable and a plain-vanilla spark plug cap (am I missing something?). I don't know what HT is or stands for, but I've never seen a much different setup than the Bandit's one, let alone understand what the advantages/disadvantages of one or the other would be. The only other ignition system I know is the magneto, but that's way obsolete...

[pmackie]

As Chris said...instead of having a HT (High Tension or as you describe, high voltage) coil mounted to the frame and connected to the plug with an insulated lead, a "Stick" coil has the HT coil mounted directly on the spark plug. I hope that helps.

[Vlad]

Oh, I got it now, thanks. I understood wrong, that "stick coil" is the frame mounted one. Makes sense in terms of space/complexity savings. I guess the technology to squeeze an efficient coil in such a confined space just wasn't there before.