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Buell Forum » 1125R Superbike Board » Archives 001 » Archive through August 17, 2010 » 1125 Rotax even or odd fire? « Previous Next »

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Puzzled
Posted on Monday, August 16, 2010 - 07:12 am:   Edit Post Delete Post View Post/Check IP Print Post    Move Post (Custodian/Admin Only) Ban Poster IP (Custodian/Admin only)

Is this engine ‘even’ firing i.e. 360 degrees between each firing, or ‘odd’ firing like typical of a V twin?
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Motorhead102482
Posted on Monday, August 16, 2010 - 09:35 am:   Edit Post Delete Post View Post/Check IP Print Post    Move Post (Custodian/Admin Only) Ban Poster IP (Custodian/Admin only)

I'm no expert and I could be wrong, but I would say that it's probably 180 degrees from each other or something like what you said of "odd" firing.
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Ratsmc
Posted on Monday, August 16, 2010 - 09:46 am:   Edit Post Delete Post View Post/Check IP Print Post    Move Post (Custodian/Admin Only) Ban Poster IP (Custodian/Admin only)

I'm not sure I understand the question.

The 1125 motor is a 72 degree single crankpin motor (both pistons attached at the same point on the crank) so the cylinders can't fire at 360 degrees.

Once I have had my coffee, I'll do the math on the actual firing unless someone already knows it.
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Motorhead102482
Posted on Monday, August 16, 2010 - 10:10 am:   Edit Post Delete Post View Post/Check IP Print Post    Move Post (Custodian/Admin Only) Ban Poster IP (Custodian/Admin only)

I think he's talking about rotation degrees between the two cylinders firing.

Obviously they're on the same crank, but he wants to know how many degrees of rotation between each cylinder firing.

(Message edited by motorhead102482 on August 16, 2010)
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Ratsmc
Posted on Monday, August 16, 2010 - 10:49 am:   Edit Post Delete Post View Post/Check IP Print Post    Move Post (Custodian/Admin Only) Ban Poster IP (Custodian/Admin only)

That was what I was guessing.

I was trying to explain why they cannot be at 360 degrees. I'm not sure that it is obvious that they are on the same crankpin since that question has come up here before.
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99buellx1
Posted on Monday, August 16, 2010 - 11:02 am:   Edit Post Delete Post View Post/Check IP Print Post    Move Post (Custodian/Admin Only) Ban Poster IP (Custodian/Admin only)

So the easy answer is: odd
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Alex
Posted on Monday, August 16, 2010 - 11:40 am:   Edit Post Delete Post View Post/Check IP Print Post    Move Post (Custodian/Admin Only) Ban Poster IP (Custodian/Admin only)

It fires like every stock XB or Harley does (beside it has a different cylinder angle). Otherwise it would be a "Big Bang Engine" which it is not.
Hope that helps.
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Puzzled
Posted on Monday, August 16, 2010 - 04:32 pm:   Edit Post Delete Post View Post/Check IP Print Post    Move Post (Custodian/Admin Only) Ban Poster IP (Custodian/Admin only)

Thank you guys, much appreciated.
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Avalaugh
Posted on Monday, August 16, 2010 - 04:42 pm:   Edit Post Delete Post View Post/Check IP Print Post    Move Post (Custodian/Admin Only) Ban Poster IP (Custodian/Admin only)

wasted spark though i would think.
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Hootowl
Posted on Monday, August 16, 2010 - 05:11 pm:   Edit Post Delete Post View Post/Check IP Print Post    Move Post (Custodian/Admin Only) Ban Poster IP (Custodian/Admin only)

Buell has used single fire ignitions for a while now, I doubt they'd go back to a wasted spark setup.
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Littlebutquick
Posted on Monday, August 16, 2010 - 05:21 pm:   Edit Post Delete Post View Post/Check IP Print Post    Move Post (Custodian/Admin Only) Ban Poster IP (Custodian/Admin only)

its half a PPR for the engine found that out when setting up my shift light so thats 2x sparks per rev
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Datsaxman
Posted on Monday, August 16, 2010 - 06:11 pm:   Edit Post Delete Post View Post/Check IP Print Post    Move Post (Custodian/Admin Only) Ban Poster IP (Custodian/Admin only)

Doing the math:

Common crankpin means 72 degrees separation between TDC for the two pistons. Could be 72 degrees between firing impulses, then (720-72) degrees until the start of the sequence. This huge gap is good for things like traction in dirt (think flat track!), and is the so-called "big bang" arrangement.

- OR - could be (360-72) degrees, then (360+72) degrees. the only differences are ignition timing and valve timing. You could grind a set of cams and modify an engine to work either way. Ignition timing is just electronics...

With two cylinders and a common crankpin, there aren't a whole lot of options!

saxman
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Cowboytutt
Posted on Monday, August 16, 2010 - 08:29 pm:   Edit Post Delete Post View Post/Check IP Print Post    Move Post (Custodian/Admin Only) Ban Poster IP (Custodian/Admin only)

Could be 72 degrees between firing impulses, then (720-72) degrees until the start of the sequence. This huge gap is good for things like traction in dirt (think flat track!), and is the so-called "big bang" arrangement.


I'm guessing that this is correct too. Anyone want to bet a "virtual beer"? -Tutt
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Mechanicsn
Posted on Monday, August 16, 2010 - 09:34 pm:   Edit Post Delete Post View Post/Check IP Print Post    Move Post (Custodian/Admin Only) Ban Poster IP (Custodian/Admin only)

Starting at #1 TDC (firing stroke) the engine then rotates 288 degrees (360-72) and #2 reaches TDC(firing stroke). Rotation continues past #1 TDC (overlap between exhaust and intake phase), continues 360 degrees and reaches #1 TDC (firing stroke again) completing the firing sequence for both cylinders (360+72). I've done the valve adjustment on a couple of these, so I know this to be so.
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Ratsmc
Posted on Monday, August 16, 2010 - 09:40 pm:   Edit Post Delete Post View Post/Check IP Print Post    Move Post (Custodian/Admin Only) Ban Poster IP (Custodian/Admin only)

Yep. That's it. It it did the "big-bang" thing (0-72) it would sound like a lumpy single.
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J2blue
Posted on Monday, August 16, 2010 - 09:48 pm:   Edit Post Delete Post View Post/Check IP Print Post    Move Post (Custodian/Admin Only) Ban Poster IP (Custodian/Admin only)

If that is the same order as an EVO twin then the following link provides a great animation:

http://www.animatedpiston.com/Evo.htm
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Jng1226
Posted on Monday, August 16, 2010 - 10:34 pm:   Edit Post Delete Post View Post/Check IP Print Post    Move Post (Custodian/Admin Only) Ban Poster IP (Custodian/Admin only)

Very cool! Thanks
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Datsaxman
Posted on Monday, August 16, 2010 - 11:57 pm:   Edit Post Delete Post View Post/Check IP Print Post    Move Post (Custodian/Admin Only) Ban Poster IP (Custodian/Admin only)

Cowboy, I wasn't guessing...on any four stroke common crankpin V-Twin, the firing gaps HAVE TO BE (A) and (720-A)-OR- (360+A) and (360-A)for a V angle (included angle for the engineers out there) of A.

Simple geometry, not guesswork.

No. Other. Choices.
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Cowboytutt
Posted on Tuesday, August 17, 2010 - 12:40 am:   Edit Post Delete Post View Post/Check IP Print Post    Move Post (Custodian/Admin Only) Ban Poster IP (Custodian/Admin only)

OK, not a "big bang" engine as I thought, but still a little uneven because if I read this right, not equally spaced firings through rotation. IE, the 288 (360-72), pause for cylinder #2, then 360+72 longer pause to start the process all over with cylinder #1 right?

So, a Ducati with a 90 degree V would be more even in firing pulses?

There is only a very slight difference in the sound of the motors. Just trying to understand.

-Tutt
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Ratsmc
Posted on Tuesday, August 17, 2010 - 01:12 am:   Edit Post Delete Post View Post/Check IP Print Post    Move Post (Custodian/Admin Only) Ban Poster IP (Custodian/Admin only)

The Ducati would be more even but still not "regular".

That said, the sound we associate with a V-Twin is irregular.
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Datsaxman
Posted on Tuesday, August 17, 2010 - 01:26 am:   Edit Post Delete Post View Post/Check IP Print Post    Move Post (Custodian/Admin Only) Ban Poster IP (Custodian/Admin only)

Cowboy, you got it...in the first paragraph, but not about the Ducati.

A Ducati (or my Guzzi) HAS TO have firing impulses separated by either (90) and (720-90) - or - (360-90) and (360+90). Usually the latter.

If by "even" you mean (360) and (360) like a vertical twin with a "360 degree" crank (both pistons moving together). The difference between the Buell and the Ducati is what you are hearing, which is the difference between (288) and (270) isn't a lot...

Assuming again that both connecting rods are on the same crankshaft journal.
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Cowboytutt
Posted on Tuesday, August 17, 2010 - 01:51 am:   Edit Post Delete Post View Post/Check IP Print Post    Move Post (Custodian/Admin Only) Ban Poster IP (Custodian/Admin only)

That makes total sense, having heard many Ducs and Buells at Laguna Seca this year. I don't think I could distinguish between them except maybe the Buell (being larger displacement in the AMA Daytona class) sounded a little deeper. Thanks! -Tutt
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Datsaxman
Posted on Tuesday, August 17, 2010 - 10:48 am:   Edit Post Delete Post View Post/Check IP Print Post    Move Post (Custodian/Admin Only) Ban Poster IP (Custodian/Admin only)

Well, yeah...that and the Buell being so much cooler. You can hear that too...
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