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New Guzzi’s firing interval ?

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Nitram View Drop Down
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    Posted: 07 Sep 2018 at 23:03
I remember kick starting my 860GTS Ducati way back in the 80s(I was in my early 20s then and a bit new to such things) and being curious about the way the pistons fired one straight after the other as they went across TDC, and then they both missed a beat as they went across the next TDC. So at idle the exhaust note was that characteristic b-bump....b-bump....b-bump that we associate with Ducatis (and Harley’s). I think it’s that uneven firing interval that gives the motor a significant part of the Ducati v-twin’s appeal, and I remember when Yamaha made the TRX850 it had the 270 degree crank, designed to mimic the Ducati’s relaxed gait and grunty feel. 
Anyway, to come to the point, I heard a modern 750 Guzzi idling at the lights the other day, and the regular bump bump bump bump exhaust beat made me think that it had even firing intervals, not like the uneven firing pulses of Ducatis and Harleys. So can someone tell me what the firing interval of v-twin Guzzi is ? Are they all the same ? Has it always been that way with Guzzis ?
Just curious. 
🤔🤔🤔🤔
Cheers,
Nitram
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jefrs View Drop Down
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Post Options Post Options   Thanks (0) Thanks(0)   Quote jefrs Quote  Post ReplyReply Direct Link To This Post Posted: 08 Sep 2018 at 01:34
From doing the tappets the V7.ii is (to TDC) compression, compression, exhaust, exhaust. 
Obviously though firing 90° apart - "ba-bump (pause) pa-pop (pause) ... "   

At low revs it's a bit like a big single, pistons firing close together, which I guess is where the torque comes from, at high revs quite obviously a twin; it spins up far quicker than a single can.   

With the idle being about 1500rpm I find it, with a bit of imagination stretch, reminiscent of a 2-stroke twin, "pocka-pocka-pocka" although without the, "ning-di-bung-bung" over run Wink
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Adam View Drop Down
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Post Options Post Options   Thanks (0) Thanks(0)   Quote Adam Quote  Post ReplyReply Direct Link To This Post Posted: 08 Sep 2018 at 09:22
Who put the bop in the bop de bop de bop.... 
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Post Options Post Options   Thanks (0) Thanks(0)   Quote Brian UK Quote  Post ReplyReply Direct Link To This Post Posted: 08 Sep 2018 at 09:51
With a parallel twin the firing strokes are 360 degrees apart. With Guzzi they are 270 and 440 degrees.
Brian.

Better 5 minutes late in this world than years early in the next.
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Post Options Post Options   Thanks (0) Thanks(0)   Quote red leader one Quote  Post ReplyReply Direct Link To This Post Posted: 08 Sep 2018 at 19:39
Who put the ram in the ram alonga ding dong.
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Post Options Post Options   Thanks (0) Thanks(0)   Quote jefrs Quote  Post ReplyReply Direct Link To This Post Posted: 09 Sep 2018 at 00:46
Parallel twin can be 360°, 270° or 180°

The Guzzi engine has the two con rods on the same crank pin so it's a little difficult to visualise the firing interval. The crank rotates clockwise viewed from the front. The con rods are 90° apart, one piston is always 90° ahead of the other (which is what I was trying to say, and failed).  The left pot is No.1, it fires at 0°. the crank rotates and the right pot No.2 piston comes to TDC at 270° (relative to No.1). At that point the left pot is already at 90° BTDC on its exhaust stroke. So the left pot has to complete 90° plus another 360° before it fires again, 450°.
Actually ignition takes place significantly Before TDC, because it takes time for combustion to develop and produce full power as it goes over TDC, but we set tappets at TDC

If one looks at this pic as if from the front of the engine, then the left pot is on the right Wink

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Post Options Post Options   Thanks (0) Thanks(0)   Quote jpc Quote  Post ReplyReply Direct Link To This Post Posted: 09 Sep 2018 at 08:49
Four stroke firing intervals always add up to 720°, two cranshaft revs to complete the cycle.

Funny how the Japanese always come up with a sexy new name like "Crossplane" or "Big Bang" for ideas that are often decades old. Helmut Fath won the 68 World sidecar title with his own design URS engine with a 0 - 90 - 180 - 270 crank, and some NRE Triumph and BSA engines largely predate Yamaha's TRX.

Some interesting articles here about the thinking that went into parallel twins, but never convinced the British industry: https://www.xs650.org.au/Technical%20Info/smoothness.htm
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Post Options Post Options   Thanks (0) Thanks(0)   Quote iansoady Quote  Post ReplyReply Direct Link To This Post Posted: 09 Sep 2018 at 10:18
That link gives a 404 for me.....


No idea why....

I see it's by Vic Willoughby whose stuff is always well worth reading. A successful bike racer (on Velos) as well as an accomplished journalist.

Ian
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Post Options Post Options   Thanks (0) Thanks(0)   Quote Dukedesmo Quote  Post ReplyReply Direct Link To This Post Posted: 09 Sep 2018 at 11:33
Originally posted by jefrs jefrs wrote:


The Guzzi engine has the two con rods on the same crank pin 


Exactly the same layout as a Ducati. 

In my experience Ducatis feel smoother because of the north-south engine layout not rocking the bike side-to-side, whilst at the same time the engines are less smooth because of the nature of the engine; lighter reciprocating mass, more aggressive cam profiles, higher compression ratio etc.  

I've got 2 Ducatis and 1 Guzzi and I'm constantly amazed at how similar, yet how different they are... 


Le Mans 2
Ducati 916

Ducati M900
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Post Options Post Options   Thanks (0) Thanks(0)   Quote jefrs Quote  Post ReplyReply Direct Link To This Post Posted: 09 Sep 2018 at 11:44
Originally posted by Dukedesmo Dukedesmo wrote:

Originally posted by jefrs jefrs wrote:


The Guzzi engine has the two con rods on the same crank pin 


Exactly the same layout as a Ducati. 

In my experience Ducatis feel smoother because of the north-south engine layout not rocking the bike side-to-side, whilst at the same time the engines are less smooth because of the nature of the engine; lighter reciprocating mass, more aggressive cam profiles, higher compression ratio etc.  

I've got 2 Ducatis and 1 Guzzi and I'm constantly amazed at how similar, yet how different they are... 




Your icon explains it perfectly.  Big smile

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Dukedesmo View Drop Down
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Post Options Post Options   Thanks (0) Thanks(0)   Quote Dukedesmo Quote  Post ReplyReply Direct Link To This Post Posted: 09 Sep 2018 at 12:26
Originally posted by jefrs jefrs wrote:




Your icon explains it perfectly.  Big smile



Guzzi; 


Ducati;


Beer
Le Mans 2
Ducati 916

Ducati M900
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Post Options Post Options   Thanks (0) Thanks(0)   Quote jefrs Quote  Post ReplyReply Direct Link To This Post Posted: 10 Sep 2018 at 11:18
My other bike is an Enfield Classic EFI. Although it's tweaked and the torque is similar to the V7 (57Nm) and has a humongously long power band, it is very different to the Guzzi too Wink Wink Wink 
Firing interval is simpler too, it goes 'thump'.
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Post Options Post Options   Thanks (0) Thanks(0)   Quote Mike H Quote  Post ReplyReply Direct Link To This Post Posted: 10 Sep 2018 at 20:27
Originally posted by iansoady iansoady wrote:

That link gives a 404 for me.....

No idea why....


Because it has a %20 on the end - which is code for a space.

Smile

"Chicken nuggets don't dance on a Tuesday."
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