Cylinder timing

Hiya, I was having a chat with my mate, and we would like to ask the more knowledgable members of the org whether the sv's cylinders fire as a close pair or evenly one after the other. To explain it better, do they fire at 12 o'clock, then 12:15 then nothing til 13:00, or at 12 and 12:30 then 13 then 13:30 if you get my drift. I reckon they sound even, but my mate says cos they are in a V shape they have to fire unevenly. But can't you make it regular with different attachment of the pistons to the crankshaft?

Hope that makes sense ,

Nick

[TSM]

Have a look at http://en.wikipedia.org/wiki/Engine_balance

There are reasons why there are certian firing orders in diffrent engine configurations.

Interesting Closest I've googled has been the ER6 which according to this article claims a 180 degree crank. Remember the ER6 is a parallel twin, and I'm guessing the 180 degree bit means that as one piston is at the top of it's cycle, the other piston is at the bottom.

The same article puts the SV at 90 degrees. Now, I'm not sure if that's referring to the timing or the physical angle of the cylinders? If it's the timing then I guess this means the SV is more "lumpy" or "big bangy".

Emphasis very much on personal guesswork here.

EDIT: Hmmm, just read TSM's wiki page and I'm a little more confused but a little more steady on the 90 degrees for the SV & 180 for the ER "fact". Ok, I really should know this - am I correct in thinking that a full 4-stroke rotation is actually 720 degrees? And therefore a twin with a 360 degree rotation would actually have both pistons at the top of the cylinder at the same time but only one of them would fire - therefore, horrendous mechanical balance but perfectly even firing time?

Okies, continuing my potentially flawed thinking:

360 degree crank

Number 1 _____ Number 2
Top (Bang) ____ Top
Middle ▼ ______ Middle ▼
Bottom _______ Bottom
Middle ▲ ______ Middle ▲
Top _________ Top (Bang)
Middle ▼ ______ Middle ▼
Bottom _______ Bottom
Middle ▲ ______ Middle ▲
(back to start)

180 degree crank

Number 1 _____ Number 2
Top (Bang) ____ Bottom
Middle ▼ ______ Middle ▲
Bottom _______ Top (Bang)
Middle ▲ ______ Middle ▼
Top __________ Bottom
Middle ▼ ______ Middle ▲
Bottom _______ Top
Middle ▲ ______ Middle ▼
(back to start)

Still trying to work out 90 degrees

Ok, guesswork 90 degree crank

Number 1 _____ Number 2
Top (Bang) ____ Middle ▼
Middle ▼ ______ Bottom
Bottom _______ Middle ▲
Middle ▲ ______ Top (Bang)
Top __________ Middle ▼
Middle ▼ ______ Bottom
Bottom _______ Middle ▲
Middle ▲ ______ Top
(back to start)

Hmm, ok the timing on the 90 degree crank could go either way dependent whether cylinder 2 is on it's way up or down as cylinder one goes bang. If it's as I've laid it out there then it's as least big bangy as it can be - ie. near perfect even firing order. If done the other way it becomes more big-bangy than the 180 degree pattern.

'Nother edit: Note that the top strokes which aren't marked "bang" are exhaust phases. Also apologies for the bold overdose, think it's gotten screwed by the uppy downy arrow graphics

Is the animation still on the org title page?

That should show you how they fire. I thought V's fired twice close together and then a long pause. The long pause giving the extra traction over a four cylinder.

I am more confused now haha, where is Sid?!

If it is twice then a long pause, why can't you hear it like Harleys?

EDIT: Ah I see the animation on the homepage now. So they are slightly out of sync, but fire alternately in terms of the four-stroke timing. End result I think: pistons going up and down almost together but about 1/4 of a revolution out of sync, and firing occuring almost opposite to each other, yet also a 1/4 turn out. hence why it sounds pretty much like opposite firing, but isn't quite.

[northwind]

This might be right, but don't quote me Some of it definately is though. Both pistons are on the same crank pin, so it's a 360 degree crank, but the pistons being offset by 90 degrees means that when one piston is at TDC the other is 90 degrees from TDC. If the same crank was placed in a boxer twin, it'd be either exactly opposed or simultaneous depending on the timing. And with beign a 4-stroke each piston fires once every 720 degrees.

TDMs are quite interesting, because they've had both 360 degree and 270 degree firing I think, redesigned to emulate a v-twin.