Is a V3 possible?

[Dilbert]

V engines in bikes are normally only V-twins, in cars they're V6, V8, or V12, the reason for being an equal number is that it helps balancing the piston thrust, across the frame V-twins, where the cylinders stick out either side (e.g. Moto Guzzi) are known for vibrations as the engine fires one way, then the other, akin to the BMW Boxer engine, in-line V-twins (e.g. Ducati) are better and don't make the bike jump from side to side 

Making an unequal number V engine can be done, but you end up with all sorts of issues with balancing rotors and weights, the Boxer engines employ a large flywheel in an attempt to smooth this out, the Honda V5 used five smaller pistons, with the V inline, but three cylinders at the front and two at the rear, I believe the main reason for this configuration was for cooling efficiency i.e. not having three cylinders hidden behind the front three and to make the engine narrower with the con-rods evenly spaced, but it's just easier to stick with twins, triple and fours in a "if it ain't broke, don't fix it" kind of logic 

There have been some successful V4 bike engines, especially the Honda VFR's https://en.wikipedia.org/wiki/V4_engine, but relatively few have had success with a V3 (Honda NS500 being the exception) https://en.wikipedia.org/wiki/V3_engine

[PTwizz]

Originally Posted by Dilbert

... it's just easier to stick with twins, triple and fours in a "if it ain't broke, don't fix it" kind of logic 

For much of my motorcycling life, inline fours were widely considered to be that which wasn't broke and didn't need fixing. Then Triumph came along with their crackpot idea to make inline triples work properly.

There's no reason why a V3 couldn't be made to work just as well as an inline 3 or a V4 or any other layout.
The question is, what is the advantage of a V3? It is argued that the inline 3 has a favourable mix of torque and power which is well suited to motorcycles. It also offers a narrower package than an inline 4 so it can be argued that it is a 'better' motorcycle engine.

Does the OP propose that a V3 offers any advantage over other configurations?

[Tigraid]

Speaking as an engineer, I cannot see any reason for a V3 over an inline 3 or a V twin or V4.  As mentioned, all it would bring is complications, extra weight for no real benefit.  It would likely not be any lighter than a well designed V4.

Triumph's triple differs from other IL4 engines not just because it uses 3 instead of 4 cylinders, but because the firing order of the crank means almost optimal torque delivery characteristics from its 120 degree firing order.  Combined with the ability to deliver torque low down where it is needed and to rev high up smoothly for power, it has formed the basis of several successful racing engines not to mention the big adventure bikes that we run around on.  The fact that Moto2 has just employed Triumph (765) triples is testament to the success of their middleweight IL3 designs.

The benefit of a Vee4 over an IL3 it could be argued is mass centralisation and lower C of G, which is presumably (along with favoured power characteristics) is one reason that the racing world employs them.  There's ways and means to lower C of G for an IL3 but unfortunately where high ground clearance is concerned (adventure bikes again) not possible without significant compromises to wheelbase and handling characteristics.

Personally, I prefer the power delivery of an IL3 for the road over most other multis, but also like Vee twins and boxers.

[Dilbert]

Speaking as another (Mechanical) engineer, though not in automotive, I largely agree with Tigraid, traditionally the advantage of a V-engine over an inline has been the additional low down torque, this is the same as in the Boxer engine, something to do with opposing, or partly opposing pistons, I'm too old to remember why exactly, it just is 

[PTwizz]

One advantage of the V configuration is the packaging. A V engine is shorter than an inline for the same number and size of cylinders. It also has a shorter and therefore stiffer crankshaft. The logical extension of the concept is the radial engine, which uses a single throw crank with multiple cylinders, providing huge quantities of smooth, low rpm torque.
They don't package so well in a bike.

[Griff]

It makes no sense really because surely the crank length will be the same as an inline 3 and a cylinder out of line with the others will only cause intake and exhaust plumbing issues that are not relevant to the inline motor.

[PTwizz]

It depends on what we think of as a V3.
If the configuration is one bank of 2 cylinders and a second bank of 1 cylinder, then the crank can be shorter than an inline 3.
If the configuration is a double V, like the Anzani, then the crank may be a single throw.
What is the designer trying to achieve? As with any design, there are a series of compromises to be made between packaging, performance, cost, etc.
So the answer to the OP's question is Yes, a V3 is possible. The next question is: What do you expect to achieve by it?

[CaptainTrips]

The way I envision this, a V3 would have six separate camshafts with three separate cam chain drives. That's got to add some weight and complexity. Imagine having to deal with 3 separate chain tensioners instead of one.

[NiK]

Originally Posted by CaptainTrips

The way I envision this, a V3 would have six separate camshafts with three separate cam chain drives. That's got to add some weight and complexity. Imagine having to deal with 3 separate chain tensioners instead of one.

Maybe time to go back to the outstandingly reliable timing gears that Honda implemented on the VFR?

[PTwizz]

...or pushrods.