Kawasaki Sportsbike Riders Club - Australia - Online Forum

Whats the real differnce with these motor styles?

Inline twins are cheaper to produce, because they only have the one cylinder head and set of camshafts. They're also favoured by a lot of bike manufacturers because they're very compact. Unfortunately they're naturally rough as guts. Their normal form has pistons opposed 360 degrees, which basically means each piston is rising and falling at the same time (the compression cycle in one cylinder is the exhaust cycle in the other). I think the Kwaka 250 twin has balance shafts to deal with this (not sure though).

That's all I know... anyone else?

90 degree v twins have perfect primary balance and usually create very good torque. And because of their primary balance have good motor longevity. ie the motor is not trying to self destruct every time the pistons go up and down.
The downside as already mentioned is higher production costs, harder for the bike designers to work with getting the balance of the bike right.
Hope this helps.

Neil

A V twin should be narrower than a parallel twin. But they have to run 4 cams vs two. A 90 degree V twin has perfect primary balance, so there is no need for any balance shafts etc. It's harder to get weight over the front with a V compared to a parallel.

A V sounds cooler!

ahh that makes sense, thanks guys

John H wrote: I think the Kwaka 250 twin has balance shafts to deal with this (not sure though).

Older ones don't (but that's going to the air cooled motors), newer ones do as also the ER5&6.

Cars have them too, our 4cly camry has 2

John H wrote:Unfortunately they're naturally rough as guts. Their normal form has pistons opposed 360 degrees, which basically means each piston is rising and falling at the same time (the compression cycle in one cylinder is the exhaust cycle in the other). I think the Kwaka 250 twin has balance shafts to deal with this (not sure though).

That's all I know... anyone else?

Actually the Gpx/zzr250's are 180' opposed as mentioned recently elsewhere on ksrc. Which would definately explain why, although a slight buzzbox from being a small motor, it is actually a rather high revving machine. Look at the CB250, that thing can redline at maybe 8500rpm or so, whereby on the zzr, it's just starting to get up & boogie at those revs and goes all the way through to 15 - 16krpm (i never had one of these so have n.f.i.)

mike-s wrote:Actually the Gpx/zzr250's are 180' opposed as mentioned recently elsewhere on ksrc.

Ahhh OK, I learn a new thing every day. But a four stroke inline twin with no balance shafts or other clever tricks has to be 360' doesn't it?

mike-s wrote:whereby on the zzr, it's just starting to get up & boogie at those revs and goes all the way through to 15 - 16krpm (i never had one of these so have n.f.i.)

Get up and boogie revs on the ZZR/GPX250 is between about 8K and 12.5K, totally beyond a CB250! Between 12.5K and 14K redline it's just noise really, and I think the rev limiter kicks in at about 14.5K. I think the 2004 model onwards now has a 13K redline - maybe Kawasaki decided the last 1000rpm just isn't worth the engine wear.

John H wrote: I think the 2004 model onwards now has a 13K redline - maybe Kawasaki decided the last 1000rpm just isn't worth the engine wear.

Sure does, it pretty much cuts out around 13.5K. I noticed that the dial also only goes to 15K too where as the older ones were printed to 16K, a waste of ink really.

ahh v twin vs inline/parralel twin...

think vtr firestorm/duke vs yamy trx 850...

the V gives more power, and gets used more in bigger bikes (due to it NOT trying to destroy itself i guess)...
just to mix it up aprilia do a 60 deg v twin too..

do u understand the configuration tho?? i notice all the boys are talking abt the mechanicals of it...and if ur nething like my GF ..when she asks, it just means she wants to kno wot they look like so she determine which one is prettier!!

parralel twin tthe 2 cylinders sit beside each other..like an inlie four..or inline triple....

v twin they face each other...just in case u were wondering...
and the v twin is MUCH prettier...

John H wrote:

mike-s wrote:Actually the Gpx/zzr250's are 180' opposed as mentioned recently elsewhere on ksrc.

Ahhh OK, I learn a new thing every day. But a four stroke inline twin with no balance shafts or other clever tricks has to be 360' doesn't it?

How do you figure that? think this way, they could configure it so that the intake stroke of say, cyl #1 is the compression stroke or even exhaust stroke of #2, the idea of the balancer shaft helps neutralise any inperfections in the rotation of the engine, the Gpx 250 definately has one of these suckers.

In any case, as long as you sort the primary (and to a lesser extent, secondary) balancing out accroding to how the engine is laid out, you should get minimal vibration, but its basically near impossible to eliminate it entirely.. And yes im well aware that the firing order of the gpx/zzr 250 is slightly asymetric, but in loosing out on perfect symmetry, they have gained engine power through smoothness.

piccy

My 1983 air cooled GPz250 has no balance shaft and pistons oppose. There are no other tricks. It is worth noting the compression is not so high and revs a bit lower than newer motors, but back then power was less so who would want to sacrifice power to drive a stupid balance shaft to make it vibrate less, isn't that is what the soft seat is for.