Firing order? Big bang?

Hi all,

Just wondering about the firing order/sequence on the SV engine, does it fire both front plugs and then both rear plugs or does it fire 1 front and 1 rear plug to balance it?

[andrewsmith]

Twins are normally a Big Bang Motor

[Sid Squid]

Twins are any way they're constructed - there's no absolute requirement for it to be made in any given way, but obviously some layouts are better than others.

The SV is constructed in the way that is most common for a 90 degree vee-twin - a common crankpin means that when one piston is at TDC or BDC the other is at midstroke, thus an SV with a standard crank could never be 'big bang', for that to be the case you'd need a different crankshaft, (that very probably couldn't fit in the cases), engineered such that both pistons were at TDC at the same time.

Not only would that require a major redesign of the engine, but it would miss out not only on the simplicity of construction that the most common design of vee-twin benefits from, but would also not have a very handy feature of the present configuration, which is that as either piston is at TDC or BDC, that is; stationary, the other is at midstroke, which is where it travels the fastest, and thus adds most to the rotational force of the crank - even when not a firing stroke.

Originally Posted by andrewsmith

Twins are normally a Big Bang Motor

To be fair I cant think of a twin big bang engine, there are many parallel twins but even the one's of those that have both pistons moving in unison (both at TDC together) have one on the top of the exhaust stroke while the other is at the top of the compression stroke.

A big bang twin would sound like a single because it would fire both cylinders together.

The closest engine I can think of is the Crossplane engine in the current R1.