Every now and then I see a little argument on Reddit or some forum about what an “inline twin” is and how it’s different to a “parallel twin”. Hearsay flies around and people make guesses.
But what’s often really misunderstood is the 270-degree crankshaft. What does it mean? Again, people often pass on what they’ve heard, or what marketing people have told them. The truth lies somewhere in between.
In this guide I’m going to go over:
- What is a 270-degree crankshaft parallel twin?
- Why use a 270-degree crank — and not a 360-degree crank, a 180-degree crank, or a V-twin?
- What are all the motorcycles that have a 270-degree crankshaft in a parallel twin format?
Are you obsessed with motorcycles?
Well, I am. That’s why I created this site — as an outlet. I love learning and sharing what others might find useful. If you like what you read here, and you’re a fraction as obsessed as I am, you might like to know when I’ve published more. (Check the latest for an idea of what you’ll see.)
What is a 270 degree crankshaft parallel twin?
Firstly, a parallel twin engine is any engine with two cylinders where they share one cylinder head. See two exhaust pipes? You have (nearly always*) found yourself a parallel twin!
* Reader Matt Carmichael commented that some motorcycles may have twin ported heads, like in the case of the single-cylinder Honda XBR500, which still has two exhaust headers.
There’s no difference between an “inline two-cylinder engine” and a “parallel-twin engine”. Or various other names I’ve heard that sound silly.
Parallel twins come in various kinds of firing order. There’s the 360-degree crank, where the pistons take even turns to fire, and the 180 and 270-degree cranks, where things are less even but more interesting.
To go over these, let’s quickly review how the four-stroke engine works.
Four-stroke engines (which make up the lion’s share of the market) have four distinct strokes (surprise!). There’s:
- Intake — sucking in the air/fuel mixture into the cylinder as it goes down
- Compression — squeezing it into a compressed area, before it’s blown up by the spark
- Combustion — the spark plug makes it go bang! driving it downwards, and
- Exhaust — it goes back up, sending the exhaust fumes out, before sucking in more fuel.
So in a single-cylinder engine, the engine rotates twice for every time the cylinder fires.
But what about in a twin? They don’t just fire at the same time, surely? Well, they could (but they usually don’t).
The 360-degree crank
The easiest configuration to understand of a two-cylinder engine is the 360-degree firing order.
In 360-degree firing order in a parallel twin, both pistons move up and down at the same time. So when moving up, one is compressing, while other is doing exhaust; when moving down, one is doing combustion, while the other is doing intake. They take turns this way.
The main advantages of 360 degree systems are that a) they run more smoothly than a single-cylinder engine, and b) you can use just one firing system (coil).
So in a 360-degree firing order, if every letter or number is 90 degrees, firing is like this: Bang, 2, 3, 4, Bang, 6, 7, 8.
The 180-degree crank
In a 180 degree firing system, the cylinders move in opposite directions.
This means that when one is going up, one’s going down. Piston one combusts as the second does compression, then piston two combusts (a half-revolution after piston one did) while piston one exhausts. That half revolution is the so-called “180-degree” difference after which this configuration is named. Both pistons now have to go through exhaust, intake, and compression again — 540 degrees before the next.
So the firing order for a 180-degree firing system is like this: Bang, 2, Bang, 4, 5, 6, 7, 8.
The advantage of a 180 degree firing system is that it’s perfectly balanced. The pistons move against each other.
One effect of a 180-degree firing order is that you get a “rocking couple” effect. It’s like when you’re rowing — when you row on the left, then on the right, the boat rocks right to left. You feel this as vibration in a motorcycle. In a modern parallel twin, like in the Kawasaki Ninja 650, the engineers counter with a counterbalance shaft. This reduces vibration, but never eliminates it.
So on a 180-degree crank engine you do have to use a balance shaft to reduce vibration, but it results in a lot more smoothness than a single or even a 360-degree engine. They do sound a little boring, though.
The 270-degree crank
In a 270-degree firing system, it’s in between. The pistons move out of step, syncopated. One piston is three-quarters of a rotation behind the other. The firing system is Bang, 2, 3, Bang, 5, 6, 7, 8.
This is the same firing order as a 90-degree V-twin (which Ducati calls an L-twin), which is why the two engine types are often compared.
Here’s the firing order of these three engine types explained visually.
But why use a 270 degree crankshaft? Good question.
Why use a 270-degree crankshaft in a parallel twin?
The advantages of a 270-degree firing order are that basically, it’s somewhere in between 180 and 360.
Not joking! It has less primary balance than a 180-degree engine (bad), but less of a rocking couple (good). It has more balance than a 360-degree engine (good), but has more rocking couple (bad).
Firstly, the most interesting thing about a 270-degree crankshaft twin is that it there’s never a piston that’s not moving. Look at the above image again. In the 360 and 180-degree configurations, there’s always a point where a piston is either at TDC or BDC and thus has to start moving again in the opposite direction.
Yamaha calls the effect of an engine never stopping being “removing inertial torque”. They call it a feature of all their “crossplane concept” engines, starting with the inline 4 of the Yamaha R1 (from 2009 onward).
Secondly, a lot of customer research by companies (and also anecdotal evidence from riders) shows that the vibrations produced by a 270-degree configuration are really… pleasant. People enjoy the net effect of the slightly lumpy sound, even though you can make almost any engine sound interesting (and it’s quite subjective anyway).
According to Triumph engineers, they considered the aesthetics of the 270-degree engine, but also considered a couple of engineering advantages. There are vibrations that are caused by forces in engines of any kind. There are primary forces, that happen once per revolution, and secondary ones, that happen twice per revolution.
Engineers have to use counter-balancers to reduce engine vibrations. In most parallel twins (all modern ones) there are counter-balancers to get rid of vibrations.
These forces can produce vibrations if they are not balanced. Engineers use primary balance shafts to balance the primary forces and also the rocking couple that can be left if no balance shaft or only one balance shaft is used.
Now, to balance the secondary reciprocating forces. Except… in a 270-degree crank layout, there aren’t any. Secondary reciprocating forces cancel one another out. That’s the magic of always being in motion.
Finally, one question you might have is “So why not do all this, but in an L-twin, like Ducati?” For three reasons (that I can think of)
- A parallel twin is easier to cool. It’s hard to coll the rear cylinder in a Ducati, or any V-twin, particularly if they’re air-cooled.
- A parallel twin is lighter. There’s just one cylinder head.
- A parallel twin is easier to maintain. Just one camshaft, and one cylinder head!
Basically, in writing this I’m going to find it hard to ever buy a motorcycle again that’s not a parallel twin. (But I do have a thing for Ducatis…)
Motorcycles with Parallel Twin 270-degree crankshafts — a complete list
The reason I started this article was mostly that I wanted to create a list of motorcycles that have a 270-degree crank. What are all the bikes out there with character? Tell me! (I know about Norton…)
Here they are, in no particular order.
BMW motorcycles with parallel twin 270 degree cranks — The F900R and F900XR
In 2020, BMW updated their F800R to the F900R, and also released the adventure tourer F900XR.
The earlier BMW F800 had a more traditional 360-degree firing order engine, but the engine in the newly released 2020 F900R and F900XR engines is a livelier 270 degree-crank motor.
The F900XR is the more adventure touring and slightly higher-spec version of the F900R (and would be my pick of the two in most markets).
Honda motorcycles with parallel twin 270-degree cranks
Honda has produced a lot of engines in its past, but it rarely has used a parallel twin — though some of its more unusual motorcycles have been V-twins.
The first Honda motorcycle that came to my mind was the Africa Twin CRF1000L, released in 2016. The Africa Twin has a 998cc parallel twin with a 270-degree crank.
The 2019+ Honda CRF1100 Africa Twin also has a 270-degree crank, and a rumored Honda Africa Twin 850 would also probably have it.
Next, obviously the 2020 Honda Rebel 1100 (one of the motorcycles that might just be my “next” has the same engine as the CRF1100 Africa Twin — albeit in detuned form. And has the same 270-degree crank obviously.
But surprisingly, Honda has used a 270-degree crank in another series of engines — the much more sedate NC700 and NC750 “street bikes”. Rumour has it that an upcoming NC850 will also have it.
Yamaha motorcycles with parallel twin 270-degree crankshafts — CP2 engines
Yamaha was the first manufacturer to make popular a 270-degree crankshaft with the TRX850, first produced in 1995. What a stunning bike! Sure, it was trying to look (and sound) like a Ducati, but I don’t care. They’re in short supply now, and sellers know that they’re cool, unfortunately.
Yamaha made a couple more parallel twin engines with 270-degree cranks, like the TDM850 and TDM900, but they haven’t been in production for a long time now.
In recent times, Yamaha brought pack the 270-degree crankshaft with their CP2 motor.
“CP” stands for “Crossplane”, which was a trademark they gave to the crazy firing order of the Yamaha R1 (see my buyers guide) that gives it that incredible sound.
The Yamaha CP2 engine is a 689cc water-cooled 4-valve-per-cylinder parallel twin with a 270-degree crankshaft (hence the “crossplane concept” designation). The “crossplane” designation is a bit weird — mostly marketing — but the CP2 engine is one of the most-loved modern engines.
The MT-07 (also known as the FZ-07 in some markets) was the wildly successful competitor to the Suzuki SV650, and yes, the MT-07 has that 689cc CP2 engine.
The XSR700, which shares the same engine as the MT-07, also benefits from the lively CP2 engine.
Finally, the Ténéré 700 has the same CP2 engine — same spec and tune, it seems.
Aprilia motorcycles with a parallel twin 270 Degree Crank — Just the RS660
Aprilia has produced a ton of V-twins and V-fours, and they’re awesome. They’re pretty much all on my “to-ride” list.
But Aprilia surprised me this year by releasing the RS660 for 2021, a motorbike with a parallel twin and a 270-degree crankshaft and definitely one of the most interesting new motorcycles of 2021. There’s a lot of praise I’m ready to sing for the RS660 — I love the re-incarnation of a middleweight sportbike with a “not ridiculous” riding position, cruise control, and cornering ABS. And the crankshaft is just icing on a very delicious cake!
Other motorcycles from Aprilia with the same engine will also have the same crankshaft (like the smaller Tuono 660).
Triumph Motorcycles with a 270-Degree Crank — Many, but it Started with the Scrambler
Triumph was also pretty early to the party with the 270-degree crank.
Traditionally, Triumph parallel twins had 360-degree cranks. These could sound pretty beastly… I’ve heard some raucous older Bonnevilles!
But it was the Triumph Scrambler (see my buyers guide) that took the same engine and said “you know what, 270-degree crank for this one” from 2006.
Triumph soon added this configuration to the Speedmaster and the America, two “moderate”-sized cruisers.
Since the 2016 rebrand of the Bonneville to the Street Twin (and the Scrambler to the Street Scrambler), all Triumph parallel twins have had a 270-degree crank. This extends to the more modern, bigger 1200cc motors — like the Speed Twin and the Scrambler 1200.
Royal Enfield — the 650 cc engines with 270-degree parallel twin engines
Lastly, just because I want to include a cheaper brand… Royal Enfield introduced a 270-degree parallel twin in their Continental GT and their Interceptor 650.
These motorcycles won’t wake the dead. In Australia, they’re learner-legal, which means they’re slow. But dang, they look smart! I keep eyeing them for maybe my next… they pack ABS, a nice engine, and all the power you need for quieter roads in a handsome and very affordable package. Could be the one. Unless a Speed Twin seduces me.
Brands missing from this list
I think it’s more interesting to note the other big brands that aren’t on this list.
I may have missed a couple (and I’m aware that Norton isn’t up there, but they keep popping in and out of existence, and their stuff is SO expensive that I think their owners know perfectly well what they own and don’t need to be told!)
- Ducati — All L-twins or V-Fours (in modern history, although they’ve done p-twins in the past)
- Suzuki — Very few twins. Generally V-twins, like the SV650.
- Kawasaki — They do have a lot of parallel twins, but these all have a 180-degree crank, like the Ninja 650.
- Moto Guzzi — These guys do all V-twins, transversely mounted
Have I got something wrong? I google a lot, but I miss things all the time. A visit to a motorcycle museum confirmed how much I just don’t know. If there’s a detail you want to correct me on, please do say hello and email me.