90 Degree V-Twin: Firing Order of 270/450?

[SmithSwede]

One of you engine gurus kindly explain this to me.  You often read that a 90 degree V-twin like our Guzzis have a 270/450 firing order.   But I don't think this can mean when the pistons fire.  So what does "270/450 firing interval" mean?  I think I'm missing a conventional meaning or reference point.

Given a common crank pin and 90 degree cylinder angle, when cylinder #1 is at TDC, then necessarily cylinder #2 is at TDC 90 degrees later.  Or if you rotate the crank the long way around, then #2 is at TDC 270 degrees later.   But a cylinder can only fire when at TDC.   Therefore, cylinder #1 must fire, followed by cylinder #2 firing 90 degrees later.   The only other possibility is #1 fires, followed by #2 firing 270 degrees later.  It's either 90 degrees, or 270 degrees, of separation in the firing points.  I'm assuming the latter, which may be what the 270 in 270/450 means.

Question 1-- So which is it?  In a Guzzi, does cylinder #1 fire and then 90 degrees later #2 fires?   Or is it that #1 fires, then 270 degrees of rotation, then #2 fires?

Question 2--By the above logic, it follows that the cylinders are *not* firing at 270 and 450 degrees, because there is 180 degrees between 270 and 450, not 90, and not 270.   

OK,so what does the 270/450 nomenclature mean? 

The only thing I can figure is that it means, by convention, that #1 fires at 0 degrees, followed by #2 at 270 degrees later, and that there is then 450 degrees of rotation from the point at which #2 is at TDC for its firing stroke until #1 returns back to TDC for its next firing stroke (i.e. 720-270 = 450).

But that seems odd for at least two reasons.  First, this would mean that "270" really does refer to a firing position, but "450" does not.  Which is confusing. 

And second, why even specify the 450 since it's obvious from the fact that #2 fires at 270 and you have to get back to zero/720 for #1 to be at TDC?  Once you state that 270 is the firing point for #2 on a common crank with 90 degree cylinder angle, why specify 450, since it's just obvious arithmetic that (720-270=450)?

[Rough Edge racing]

 I have a Ducati, it's said the V8 like sound, same as Guzzi, comes from the firing order...V-8's fire every 90 degrees.. But the Guzzi/Ducati  firing is said to be 270-405  ...135 degrees????

[oldbike54]

 Prescott , what is confusing you is the left hand cylinder fires first , not the right hand cylinder .

 Dusty

[Rough Edge racing]

Prescott , what is confusing you is the left hand cylinder fires first , not the right hand cylinder .

 Dusty

  So each cylinder fires every 720 degrees  with a 90 degree phasing between cylinders?

[Phang]

I guess 270/450 is referring to the intervals between two bangs in degree.

if you take cylinder #1 as the first bang, the second bang is 270 degree later.

if you take cylinder #2 as the first bang, the second bang is 450 degree later.

[nc43bsa]

  So each cylinder fires every 720 degrees  with a 90 degree phasing between cylinders?

Yes.

[nc43bsa]

Maybe this will explain the differences:

https://en.wikipedia.org/wiki/Big-bang_firing_order

[SmithSwede]

Kirby--not being argumentative, but the Guzzi simply cannot have 180 degree between TDC firing events.  The cylinders are 90 degrees apart.   Therefore, since firing must occcur at TDC, firing must be separated by 90 degrees (going around the short way) or 270 degrees (going around the other, longer way).

That's what bugs me!

But you are totally right--the engine is magical, and it doesn't matter if you understand the geek stuff to appreciate the magic.

[pete roper]

The crank rotates clockwise when viewed from the front.

Left hand pot can be #1 so it fires, at that point the RH cylinder, #2 is on its induction stroke but the crank rotates through 270 degrees to bring #2 up to TDC compression.

#2 then fires and at that point #1 is on the of exhaust stroke but has the entire induction and compression cycle to go, plus the end of the exhaust stroke. So another 450 degrees before #1 fires again.

Each cylinder has a 720 degree cycle. I don't see what's so hard to understand???

Pete

[nc43bsa]

Maybe this will help?

https://www.youtube.com/watch?v=v70MXzekosw

[leafman60]

Smithswede, your original question is not a stupid one and your confusion is very understandable.

Firing order for any engine depends on its cylinder layout and crank pin configuration. The degrees between the cylinders, the number of crank pins on the crankshaft and the angles between them all determine the firing order.

The Guzzi is a V-twin with 90 degrees between the cylinders and both pistons connected to a single crank pin on the crank shaft. One cylinder fires 270 degrees after the preceding one whose next firing is then 450 degrees later.

https://www.youtube.com/watch?v=ZQuqkh3ZEo4

These motors could have valve timing set so that the cylinders fired in quick succession, 90 degrees apart, with a long spin in between but they are not.

By juggling crank pins stagger, manufacturers can produce engines of many different cylinder configurations to have virtually any firing order they desire.

[Huzo]

The Gizzi has a 180 deg separation between firing. In other words the cylinders  fire 180 deg apart.

Ummmm Does that need a re think ??? Just for the sheer fun of it, grab a 2 metre tape measure and lie it on a piece of paper. Zero is your start point. Make a dot at 90 mm (that's a representation of 90 degrees) and another one every 720 mm from that point on for a couple of metres, they can be the ignition points for cylinder #1. Now go back to the zero and count forward 360 mm (one crank rotation)and make a dot 180 deg after that ( 360+180=540) now you have a dot where number two fires so measure forward 720 mm from there and do that for a couple of times. What you will now see is a linear representation in mm of the circular rotation of the crank in degrees. You will notice the "loping" interval so obvious to the ear. There's nothing wrong with trying to understand more about your bike, and the suggestion to "just ride it" is a decision for you to make for yourself. If you want to do what I suggest and follow the plan, you'll see what I mean. Remember that each cylinder fires 720 deg after it's previous ignition. If people "just rode" their bikes, there'd be no upgraded maps, or plates in the sump, or good advice on rollerising 8V motors. I'm being careful not to " shit anyone to tears" , or paint them as oracles, but lucky for us that there are people with enquiring minds. We are better for it..

[pete roper]

Nobody is suggesting the question is stupid, it's just it is really quite simple when you sit down and think about it. Probably drawing a diagram for yourself with a protractor might make it easier.

Pete

[Huzo]

?Have you never adjusted the valves on your Guzzi?

 :-)

Does that actually mean anything ? That's un related and immaterial. Was there a point somewhere in there?

[kidneb]

OK,- my version

When you describe the firing order, you have to start somewhere. Not starting with the crank position of one cylinder firing would be confusing.
As Dusty points out, the LH cylinder is the #1 cylinder. And with LH cylinder just firing, that is point 0 - zero degrees, the starting point.

And then,- after 270 degrees of crank travel, the RH cylinder fires.
And then,- after 450 degrees of crank travel, the LH cylinder fires.

 

       

[Phang]

Yes you are correct, I ment to start the crank rotation from 45 degrees from the top! I will correct.

Thanx

 I have removed my reply with quote of your earlier reply, so that it won't further confuse those who are confused 

I never take the guzzi engine timing seriously until the timing chains of my mate's Stelvio dropped during the rollerisation.

A sketch on greasy paper during coffee break helped me understand the firing order and timing of the 8V engine.

Hardest part was convincing my mate to have faith in me before we thumbed the started button.

[oldbike54]

OK,- my version

When you describe the firing order, you have to start somewhere. Not starting with the crank position of one cylinder firing would be confusing.
As Dusty points out, the LH cylinder is the #1 cylinder. And with LH cylinder just firing, that is point 0 - zero degrees, the starting point.

And then,- after 270 degrees of crank travel, the RH cylinder fires.

And then,- after 450 degrees of crank travel, the LH cylinder fires.




 

       

 Yeah , kinda thought that explained it , guess not LOL

 Dusty

[SmithSwede]

Well, here's where I have arrrived.   

Let zero degrees be the reference point, with #1 left cylinder at TDC and beginning its power stroke.

#1 fires and the crank then rotates the "long way around" for 270 degrees until cylinder #2 is at TDC and ready for its firing stroke.

The crank then rotates ALL THE WAY back to the starting point, i.e. back to zero, or what you might call 720 degrees.  Only then is #1 cylinder again back at TDC and ready to begin its power stroke.   

Here's the source of the confusion.   If zero is the reference point, with #1 at TDC for its firing stroke, then "270" really is the number of degrees (from reference point zero) at which #2 is at TDC and ready to do its firing stroke.

But it is false to say that #1 fires again at 450 degrees (meaning 450 degrees from the zero reference point).  In fact, nothing can fire at 450 degrees because #2 is at BTDC and #1 is halfway between TDC and BTDC. 

It is also false to say that #1 and #2 ever fire 180 degrees apart.  No, they fire 270 degrees apart, and then 450 degrees apart (360 for 1 full revolution + another 90 degrees to account for the 90 degree cylinder bank angle).   They can't fire 180 degrees apart, since that's geometrically impossible.

To my way of thinking, it would be less confusing to say that the firing order is 0-270-720.   

But Phang is absolutely correct---"270/450" makes sense if you read that as the "intervals in degrees between bangs."   But it is just false to read "270/450" as "when the cylinders fire in relation to a zero reference mark."

[twowings]

I like bacon...

[Chuck in Indiana]

I like bacon...

Wrap some cheese and little smokey stuffed jalapenos with it and smoke it for two hours.. 
 

[twowings]

will do...

[Chuck in Indiana]

I think everybody's saying the same thing in different ways.  Except for the bacon..

[nc43bsa]

If that jet plane were on a giant treadmill, would it be able to take off?   

[LowRyter]

Wrap some cheese and little smokey stuffed jalapenos with it and smoke it for two hours.. 
 

ABTs + Chuck's Chicken Wings  made a great Sunday night with my two sons.   

[LowRyter]

Ok, this is my last shot 'cause I'm leaving on a jet plane!

Every 720 degrees of rotation of the crank the cylinders fire one time..at position 270 degrees and 450 degrees. I think that that is 180 degrees apart.

Done.

:-)

sorry the difference from #1 & #2 isn't 180, it's 450.  Then another 270 back to #1.

I think folks have confused subtraction with addition. 

Imagine that your engine is a clock, start at 12 0'clock and go to 9 o'clock (#1 fires), then back around to 12 O'clock the SECOND time (#2 fires) and start all over again.

[Huzo]

sorry the difference from #1 & #2 isn't 180, it's 450.  Then another 270 back to #1.

How very right you are !

[LowRyter]

How very right you are !

unfortunately, I'm the guy here with no mechanical aptitude.   

[Huzo]

unfortunately, I'm the guy here with no mechanical aptitude.   

Mechanically you may be shithouse, but you've got basic mathematics sorted

[rodekyll]

Did someone say bacon?   

[oldbike54]

Did someone say bacon?   

 And hushpuppies 

 Dusty