Big bang engine - Kawasaki Versys Forum
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post #1 of 33 (permalink) Old 03-06-2013, 09:14 PM Thread Starter
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Big bang engine

Okay, let me try to sum this up. This being the facebook happy society that it is, I figured I'd do the Versys a solid and find their page and "like" it (I really do like it though After doing so, I read the little blurb they have on the main page and found this:

"The engine uses a 180 degree crankshaft. This in turn requires an uneven firing interval (180 degrees, 540 degrees) which gives the engine note a distinctive "throbbing" sound at idle."

which, come to find out, is a wikipedia entry. The uneven firing part was a link that I clicked on that has sent me on my current journey. The link draws from here http://en.wikipedia.org/wiki/Big-bang_firing_order Which summarizes what the whole big bang thing pretty well.

I'm even happier knowing that the Versys employs this technology but I need to be able to conceptualize what's going on inside the cylinders to really satisfy my curiosity.

WHAT does a 180 degree crankshaft in a parallel twin look like?
WHERE and WHEN exactly are the cylinders firing when they say it has a 180, 540 degree firing pattern?
I'm guessing they're using 540 as the double of 270, but where is 540 and 270 inside the cylinder? or does that even refer to the cylinder? Anybody have some expertise in this area?
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post #2 of 33 (permalink) Old 03-06-2013, 10:30 PM
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When left piston (#1) is at TDC, right piston (#2) is at BDC at 180 degrees of crankshaft rotation ahead of #1, so when one piston is all the way up, the other one is all the way down... Cylinder #2 fires 180 degrees after cylinder #1. It's a four stroke engine, so piston #1 has to travel back up (180 degrees), back down (180 degrees), than back up (180 degrees), for a total of 540 degrees crankshaft rotation for #1 to fire after #2.

So in effect, you get a "Bang, Bang, .... , .... , Bang, Bang, .... , .... , Bang, Bang, .... , .... ," and so on.
Crankshaft Degrees: ....... 0---180----------------540---180----------------540---180-------------
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Last edited by invader; 03-07-2013 at 07:02 AM.
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post #3 of 33 (permalink) Old 03-06-2013, 11:09 PM Thread Starter
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AHA! That makes sense! Thank you very much! I was trying to relate the rate of degree to a circle and was really wondering how they got that many degrees.

The big bang mechanics made sense, I was just trying to figure out what the Versys' engine was doing. Google was not helping.

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post #4 of 33 (permalink) Old 03-07-2013, 12:40 AM
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So thats where that sound comes from. I must say that the stock exhaust is not grand at showing the sound off. But an aftermarket sounds mean.

Also here is a picture for comparison.
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post #5 of 33 (permalink) Old 03-07-2013, 05:59 AM
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for digging facts .

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post #6 of 33 (permalink) Old 03-07-2013, 06:45 AM
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Straight-twin Engine

Crankshaft angle

There are three main crankshaft configurations for this engine: 360, 180, and 270. There are minor differences in the applications for four stroke and for two stroke engines, largely pertaining to ignition intervals. For example, the 360 twin is the natural configuration for a two cylinder four-stroke engine, since four piston strokes add up to 720. The below will mostly be concerned with four-stroke engines.

In a 360 engine, both pistons rise and fall together. The dynamic balance is identical to that of a single-cylinder engine, but with twice the number of ignition pulses. The firing order is offset, so that cylinder 2 fires 360 degrees after cylinder 1, and 360 degrees later cylinder 1 fires again at 720 total degrees, the beginning of another four-stroke cycle.

In a 180 engine, one piston rises as the other falls. This gives good primary balance, albeit with a rocking couple; but results in irregular ignition pulses. This is because cylinder 2 fires 180 degrees after cylinder 1, and cylinder 1 doesn't fire again for another 540 degrees - always adding up to the 720 degrees of rotation for a four-stroke cycle.

In a 270 engine, one piston follows three quarters of a rotation behind the other. This results in a mixture of the imbalances in the first two types and yields firing intervals identical to a 90 V-twin. Firing order here is that cylinder 2 fires 270 degrees (3/4 of a rotation) after cylinder 1, and cylinder 1 fires again 450 degrees (one and a quarter rotations) after cylinder two, again at a total 720 degrees and the beginning of the next cycle.

360 and 180
From the 1930s, following the work of Val Page, most British four-stroke parallel-twin motorcycles used a crank angle of 360, which allowed the use of a single carburettor because 180 and 270 twins need twin carburettors, as did an early Meguro was a copy of the 360 British BSA A7. However, in the 1960s Japanese manufacturers favoured the 180 whose smoothness allowed higher rpm and thus more power. For example, the 1966 Honda 450 cc dohc 180 parallel-twin “Black Bomber" could challenge contemporary British 650 cc 360 twins.

Many small motorcycles of less than 250 cc use a 360 crankshaft as the vibration issue was less significant; examples includes Honda's CB92, CB160, CA72, CA77s, and CM185. Larger twins over 500 cc, such as the Yamaha's XS650 and TX750, have used 360 crankshafts, but such parallel twins tend to feature balance shafts. The Honda CB-series in the 250 to 500 cc range used 180 crankshafts. Both the 1973 Yamaha TX500 and the 1977 Suzuki GS400 featured a 180 crankshaft and a balance shaft, while the 1974 Kawasaki KZ400 used a 360 crankshaft and a balance shaft.

A 180 crankshaft engine suffers fewer pumping losses than a 360 twin, as displacement in the crankcase stays roughly constant. However, a 180 engine requires a separate ignition system, points or otherwise, for each cylinder. The 360 twins can have a single ignition system for both cylinders, with a wasted spark on each cylinder's exhaust stroke. The BMW F800 parallel twin motorcycle is a 360 design. Inherent vibration in the BMW F800 means its engine is limited to 9,000 rpm. BMW reduced the vibration using a third "vestigial" connecting rod to act as a counterbalance.

270
A modern development of the straight-two engine is the 270 crank, which imitates the sound and feel of a 90 V-twin, but requires a balance shaft to reduce vibration. Effectively, the 270 crank is a compromise which allows a more regular firing pattern than a 180 crank and less vibration than a 360 crank. As with a 90 V-twin, the pistons in a 270 inline twin engine are never both stationary at the same time, thereby reducing the net momentum exchange between the crank and pistons during a full rotation. The oscillating momentum manifests itself as an oscillating crank rotation speed, which, when paired with a driven-wheel rotating at the more steady road speed, will introduce an oscillating torque in the drivetrain and at the tyre contact patch.

Phil Irving undertook to minimise this oscillating torque, and for one particular connecting rod to stroke ratio, arrived at an optimal separation of 76 (294), instead of the 90 (270) described above. The optimum for two pistons is found when one piston is travelling fastest at the same time the other has stopped; maximum piston speed occurs when the connecting rod and crank throw are at right angles, not when the crank throw is at 90 to the cylinder bore. This minimisation of so-called inertial torque was also one of the goals Yamaha achieved with its "cross-plane" R1 engine. Note that in neither case was the oscillation completely eliminated, only reduced significantly.

http://en.wikipedia.org/wiki/Straight-twin_engine

Last edited by invader; 03-07-2013 at 06:49 AM.
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post #7 of 33 (permalink) Old 03-07-2013, 07:28 AM
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Originally Posted by invader View Post
When left piston (#1) is at TDC, right piston (#2) is at BDC at 180 degrees of crankshaft rotation ahead of #1, so when one piston is all the way up, the other one is all the way down... Cylinder #2 fires 180 degrees after cylinder #1. It's a four stroke engine, so piston #1 has to travel back up (180 degrees), back down (180 degrees), than back up (180 degrees), for a total of 540 degrees crankshaft rotation for #1 to fire after #2.

So in effect, you get a "Bang, Bang, .... , .... , Bang, Bang, .... , .... , Bang, Bang, .... , .... ," and so on.
Crankshaft Degrees: ....... 0---180----------------540---180----------------540---180-------------
A clear, straightforward explanation of a mechanical process.


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post #8 of 33 (permalink) Old 03-07-2013, 08:23 AM
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post #9 of 33 (permalink) Old 03-07-2013, 10:08 AM
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are those degrees Fahrenheit or Celsius?

I'm no diplomat
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post #10 of 33 (permalink) Old 03-07-2013, 11:44 AM
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are those degrees Fahrenheit or Celsius?
Good question. I was going to ask if they were metric or standard degrees.?
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post #11 of 33 (permalink) Old 03-07-2013, 11:47 AM
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are those degrees Fahrenheit or Celsius?
Left-handed, reverse thread metric with a Whitford adapter.


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post #12 of 33 (permalink) Old 03-07-2013, 12:29 PM
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Good and interesting explanations all around! I read a few years ago that one reason Kawasaki went with the 180 crank for the V was because it was "half the Ninja 1400" crank, so they could save on design/machining/production costs.

I learned something new here on the rev ability of 180.

So, it says above that the 270 degree twin will experience "oscillating momentum... ...oscillating crank rotation speed, which, when paired with a driven-wheel rotating at the more steady road speed, will introduce an oscillating torque in the drivetrain and at the tyre contact patch." OK, I can picture that.

Questions come to mind:

1) Is that helpful for traction/grip and harmful to the drivetrain? Or is it just a mechanical curiosity? [For a street bike]

2) For a 180 twin, wouldn't its "lumpy" power pulses cause a slowing and speeding up of the crankshaft too? Wouldn't that cause oscilations in the drive train too?

3) Would a 270 twin rev higher than a 360 but lower than a 180?

To me, my gut sense tells me that the 270 (or the 294) would be the most energy efficient / highest output / least vibration. I'm assuming it could physically rev like a 180. I just guessing here. ?

Also, I have a vivid memory of when I was in my early teens (in the '60's) ...seeing and hearing the stuttering sound of an open piped Honda CB twin
!!! I thought it was pretty cool! I knew it was different from a Bonneville (360) sound. I recall that the Honda was red and chrome, high pipes on one side, maybe a 160 or 250 or 305.
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post #13 of 33 (permalink) Old 03-07-2013, 01:50 PM
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post #14 of 33 (permalink) Old 03-07-2013, 09:05 PM
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Good and interesting explanations all around! I read a few years ago that one reason Kawasaki went with the 180 crank for the V was because it was "half the Ninja 1400" crank, so they could save on design/machining/production costs.

I learned something new here on the rev ability of 180.

So, it says above that the 270 degree twin will experience "oscillating momentum... ...oscillating crank rotation speed, which, when paired with a driven-wheel rotating at the more steady road speed, will introduce an oscillating torque in the drivetrain and at the tyre contact patch." OK, I can picture that.

Questions come to mind:

1) Is that helpful for traction/grip and harmful to the drivetrain? Or is it just a mechanical curiosity? [For a street bike]

2) For a 180 twin, wouldn't its "lumpy" power pulses cause a slowing and speeding up of the crankshaft too? Wouldn't that cause oscilations in the drive train too?

3) Would a 270 twin rev higher than a 360 but lower than a 180?

To me, my gut sense tells me that the 270 (or the 294) would be the most energy efficient / highest output / least vibration. I'm assuming it could physically rev like a 180. I just guessing here. ?

Also, I have a vivid memory of when I was in my early teens (in the '60's) ...seeing and hearing the stuttering sound of an open piped Honda CB twin
!!! I thought it was pretty cool! I knew it was different from a Bonneville (360) sound. I recall that the Honda was red and chrome, high pipes on one side, maybe a 160 or 250 or 305.
The Honda 250 and 305 twins came in two flavors. The CA square headlight models were single carburetor and had a 360 crank. The Superhawk and Scramblers were dual carbed and had a 180 crank.

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post #15 of 33 (permalink) Old 03-08-2013, 08:52 AM
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The Honda 250 and 305 twins came in two flavors. The CA square headlight models were single carburetor and had a 360 crank. The Superhawk and Scramblers were dual carbed and had a 180 crank.
Cool. It was red and chrome CB, with a round headlight, telescoping front forks (not the old leading link type fork with the large swoopy fender).
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post #16 of 33 (permalink) Old 03-08-2013, 09:31 AM
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The 180* crank is one reason I bought the V.

Its important to me.

Besides I have ridden the old parallel twins with a 360 crank and they would vibrate you off the bike. NO thank you.

This bike is smooth as a twin can get especially in the 6K range and up.

My Dads 1937 John Deere Tractor was 175 Cubic Inch twin with a 180* crank. It had no muffler and sort of sounded like a harley but didn't turn many RPM at all. If I lugged the crap out of it, the two cylinders firing right after each other would give a pretty good jerk, then coast until they fired again.

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post #17 of 33 (permalink) Old 03-08-2013, 09:45 AM
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The 180* crank is one reason I bought the V.

Besides I have ridden the old parallel twins with a 360 crank and they would vibrate you off the bike. NO thank you.

This bike is smooth as a twin can get especially in the 6K range and up...
+1 I had owned a '76 Yamaha XS 650 for several years (360 crank). Lotsa shakin goin on there! (No counter-ballancer either). That motor had character, but I really appreciate my smooth V!

The XS has a splined connector (13 splines) connecting the right and left cranks. Some guys have modified their XS engines to a "near 270" crank (284 I believe) by pressing out that spline and reconnecting close to the 270 point, and then cut and realigning the overhead camshaft the same amount. They said that it made the engine run smoother, but with less torque. I don't understand you they would get less torque though.
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post #18 of 33 (permalink) Old 03-08-2013, 09:58 AM Thread Starter
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Found this pic. It's a decent visual of how the big bang lends to better tire traction.

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post #19 of 33 (permalink) Old 03-08-2013, 01:03 PM
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My Dads 1937 John Deere Tractor was 175 Cubic Inch twin with a 180* crank. It had no muffler and sort of sounded like a harley but didn't turn many RPM at all. If I lugged the crap out of it, the two cylinders firing right after each other would give a pretty good jerk, then coast until they fired again.
Maybe that explains why I feel the Versys sounds like an old JD when you crack the throttle right off idle.

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post #20 of 33 (permalink) Old 03-08-2013, 02:23 PM
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The Honda 250 and 305 twins came in two flavors. The CA square headlight models were single carburetor and had a 360 crank. The Superhawk and Scramblers were dual carbed and had a 180 crank.
I remember the sound that a much-modified Honda 305 (or 350?) on megaphones made when I was at "Dragfest" in England in 1965. I was drag-racing a Triumph 650 on megaphones back in Alberta, and the sound of the Honda was AWESOME in comparison (and MUCH LOUDER!).

Now I understand WHY.

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