Gents and whingers, and Ladies,
The new Yamaha R1 has been released utilising the use of a cross plane crank.

"How does that effect me?" I hear you ask. Well, in a nut shell, i guess it doesn't, but if you want to understand the different characteristics of engines and why manufacturers do the things they do, then read on.

Also, it doesn't hurt to broaden your engine knowledge beyond that of Magnas.

Well, i had had heard people talking about the new cross plane crank in thew new R1 and wondered what was so special about it and why it was such a significant thing.

I came across an article in the a British mag, "Superbike" and would have have shamelessly copied it it down, word for word but after re reading it, it spouts on with a fair bit of crap. So what you get is a picture of a normal crank, and an R1 cross plane crank and my explanation of the two as i understand it.

Conventional(flat plane) 4 Cyl crankshaft
http://www.youtube.com/watch?v=MxJ-pnwxp-0

So you can see in this image how the 2 middle cylinders are phased together and the 2 outer cylinders are phased together as well. This is called a "flat plane crank". Basically because you have 2 pairs of pistons timed at 180 degrees to each other and if you looked at it from the end, it would appear flat-ish. If it were a common parallel twin, the pistons would be phased together (unless of course you are a TRX850 and your pistons are actually phased 270 degress apart, and there maybe some others).

R1 Cross Plane crank
http://www.yamaha-motor.com/assets/content/images/600/09SPBK_YZFR1_blue_D1_002_7bc2bfdc.jpg

With the cross plane crank, you can see how each piston journal is phased at a different position. Lets say piston no 1 is at top dead centre(TDC). That means piston no 2 is at 90 deg after TDC, no 3 is 90 deg before TDC and piston no 4 is at bottom dead centre(BDC). Looking at it end on, it basically resembles the shape of a cross.

Were it a 180 degree crank, and piston no 1 was at TDC, pistons 2 and 3 would be at bottom dead centre, and no 4 would be at TDC. That's not to say that each set of pistons would fire at the same time as each piston would be on a different stroke in its cycle, either induction, compression, ignition or exhaust.
This design causes the crank to change speed during each rotation as each set of pistons change direction as the crank rotates. During each revolution of a flat plane crank, all 4 pistons momentarily stop moving as the crank passes TDC and BDC, this causes the crankshaft to lose momentum until one of the cylinders fires and speeds it up again. This creates a pulse in the power delivery. In a cross plane crank, only 2 pistons stop moving at any given time, in the case of the R1 no 1(TDC) and no 4(BDC) will be paired but 180 degrees out of phase, followed by no 3 and no 4. This provides and uneven gap in between each cylinder firing and as such produces a longer power band per revolution, as opposed to 2 pulses per revolution in a 180 degree motor.


Due to the uneven firing order and characteristics, a balance shaft is needed to help mimimise vibration in the motor. A v8 cross plane crank is essentially perfectly balanced and the eliminates the need for a balance shaft(s). I do know a little more but wish to understand it a bit further before i go spouting on about it on a public forum. Also, if you feel i have got any of this wrong, or wish to add to it. Please feel free to do so. I'm always up for learning.

I only know a little bit about how engines actually work but why hasn't this always been done? I thought that's the way all engines worked, (e.g. a 4 cyl with all 4 pistons with a 90 deg difference in stroke at any given time)

Nice writeup, I learned something :)


I only know a little bit about how engines actually work but why hasn't this always been done? I thought that's the way all engines worked, (e.g. a 4 cyl with all 4 pistons with a 90 deg difference in stroke at any given time)

Have a look at Ol' Fart's avatar, you can see that 1 and 4 pistons are at TDC on the block that's in the picture :)

I only know a little bit about how engines actually work but why hasn't this always been done? I thought that's the way all engines worked, (e.g. a 4 cyl with all 4 pistons with a 90 deg difference in stroke at any given time)

You'd think they would have been doing it ALOT more by now wouldn't you..

They do have a 90 Degree difference, but that is only in the order they fire..

The Yamaha R1 crank is basically a marketing exercise to cash in on Yamaha using a similar crank in their Moto GP M1. In Moto GP the big bang engines spread the power pulses and this makes life a little easier for the rear tyre, so lap times are more consistent right to the finish of the race.

In the R1 road bike the balance shaft adds weight and slows engine acceleration like a heavy flywheel. In the M1 engine vibration isn't such an issue so there isn't any balance shaft. In World Superbike they don't have to run with the balance shaft so the R1 is doing OK but in other Superbike series the R1 is dead slow and right off the pace. Not all due to balance shaft though. The R1 has other issues.

Yamaha used the 5 valve head for years too as a marketing thing. 4 valve is a better design for performance and economy.

Not all V8s have a cross plane 90 deg crank. Some V8s use a single plane 180 deg crank like that in a straight 4 engine. Most purpose built race V8s and high performance road cars like Ferrari have 180 deg cranks.

Cheers,
Alan

The exhaust note sounds cool on the r1 aswell as the moto gp m1. very flat drone compared to a screaming in-line four.
Honda used a big bang engine back in the early ninetys on there 500 cc bike(firing all four cyclinders in 90 degs)
As alan said it gives the rear tyre a easier life & the engine exhaust note sound great

Nice writeup, I learned something :)



Have a look at Ol' Fart's avatar, you can see that 1 and 4 pistons are at TDC on the block that's in the picture :)

Just posting so you can see the avatar

Youll notice 1 piston is all the way out................no crank

Well Lads,
im too drunk to make sense right now. I will read your replies, ponder and then retort on the morrow.