Yamaha 3 cylinder - cross plane crank?

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dunno58
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The 3 cylinder engine that Yamaha unveiled at Intermot apparently has a cross plane crank. What exactly does this mean for a 3 cylinder? if they are referring to a 120 degree crank then its just a normal 3 cyl, and if they are referring to a 180 degree crank then why use that over 120... Also, I believe the 120 degree crank angle would eliminate inertial torque just like the r1 cross plane crank... so if its not 120 then what is it?

pittsy
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Re: Yamaha 3 cylinder - cross plane crank?

Dunno58 said: "if they are referring to a 120 degree crank then its just a normal 3 cyl, and if they are referring to a 180 degree crank then why use that over 120"

I thought the same thing re 120 degrees but then reasoned a) it's not really a cross and b) Kevin would have told us that(?).

Surely 180 degrees is a flat plane crank?

Will it have a fourth crank pin maybe? And do something similar to the BMW arrangement? Intrigued.

dunno58
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Re: Yamaha 3 cylinder - cross plane crank?

Fair point about 180 being flat. A 120 crank has perfect balance apart from the rocking couple, which requires a balance shaft spinning at crank speed. I think that any other crank configuration is going to be less well balanced than this. The fourth crank pin thing... could be but why not just make it 120! kinda like the bmw - I don't know how well it works and what it feels like to ride but most other modern big bore parallel twins just have a 270 crank that works fine. I think with BMW its just them being different for the sake of it.

pittsy
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Re: Yamaha 3 cylinder - cross plane crank?

"It is the philosophy where "crossplane" means the kind of torque character that gives riders the exact torque they want when they need it".

Seems maybe a cross need not be a cross after all. To Yamaha, "cross plane" seems to mean low inertial torque, above all else. With a three cylinder that could be 120 degrees. Not so much "cross plane" as " across planes".

kevash
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Re: Yamaha 3 cylinder - cross plane crank?

dunno58 wrote:
The 3 cylinder engine that Yamaha unveiled at Intermot apparently has a cross plane crank. What exactly does this mean for a 3 cylinder? if they are referring to a 120 degree crank then its just a normal 3 cyl, and if they are referring to a 180 degree crank then why use that over 120... Also, I believe the 120 degree crank angle would eliminate inertial torque just like the r1 cross plane crank... so if its not 120 then what is it?

There is a cross-plane crank feature here, which might help with some of this:
http://www.ashonbikes.com/cross-plane_crank

...but I'm not sure either exactly what Yamaha means by a cross plane three cylinder yet - there was no more information forthcoming in Cologne, but we'll be hearing more about it I think by Spring 2013.

A conventional 120 degree crank vibrates in the primary harmonic, as mentioned, in a rocking couple about the centre of the crank, which can be countered by a single balance shaft. But with Yamaha's recent history this new layout seems to be about eliminating inertial torque and isn't to do with balance. A cross-plane design would have two crank throws set 180 degrees apart with one in between at 90 degrees to the other two, so viewed from the end the crank throws would create a cross when lines are drawn through them and the crank centre. It would be the same as Yamaha's cross plane four in the R1, minus one crank throw... unless there is a fourth throw, which would drive a fourth conrod connected to a counterbalance 'dummy' piston. I did think looking at the engine that it has a surprisngly deep sump, but the dummy piston being here would explain that. BMW does the same in its F-series twins:
http://www.ashonbikes.com/bmw_engine_balancer

I'm not convinced about this but it does explain some things. A conventional 120 degree triple does suffer from inertial torque fluctuation, not as bad as a flat plane four but a lot more than the near-zero of a cross-plane four like the R1 (or indeed a 90 degree V-twin). A cross-plane triple with counter balance dummy piston would have the same almost zero inertial torque of the R1, but it would probably also need the complex balance shaft of the R1 to reduce vibration, making it a costly engine to manufacture.

Alternatively, you might be able to mimic a cross-plane four by having one piston of the cross-plane three weighing twice as much as the other two. This seems bizarre at first, and it would certainly limit the rev ceiling and have other knock-on effects, but I'll look into that as a possibility too. I'll produce a feature about the new triple, and another about Yamaha's future, in the coming days.

kevash
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Re: Yamaha 3 cylinder - cross plane crank?

A bit more on this: Very specifically, Kunihiko Miwa (designer of the original R1 and one of the men behind the change in mood at Yamaha) said this "...means the kind of torque character that gives riders the exact torque they want when they need it."

In other words, this is definitely a zero inertial torque design, that's exactly how the cross-plane R1 was described. In turn, that means it's not a 120 degree crank unless they've come up with some kind of reciprocating counterweight system that eliminates the inertial fluctuations. That seems unlikely and also doesn't fit with the cross-plane description or link with the R1 so neatly. So I'm more convinced that it's a genuine 90-degree cross plane like the R1 with a missing cylinder, although I can't see how they cam fit in the additional crank throw needed for a dummy piston. But the sump does look deep enough... Or maybe my double-mass piston idea isn't so daft after all....

pittsy
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Re: Yamaha 3 cylinder - cross plane crank?

Who's to say all three cylinders need to be the same cc?

kevash
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Re: Yamaha 3 cylinder - cross plane crank?

pittsy wrote:
Who's to say all three cylinders need to be the same cc?

Yes, I wondered about that too, but one would need to be far bigger to have a piston of double the weight, yet the engine on display was compact and the cylinders almost symmetrical. It's the 'almost' which gives us a clue, and I think I've come up with something, I'll put a feature online later today...

Dean15
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Re: Yamaha 3 cylinder - cross plane crank?

Remember the Laverda 1000 3-cylinder models of the 70's.

Some had 120 cranks, some had a flat crank with two up; one down. I can't think what the advantage of the latter arrangement might be.

shuggiemac
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Re: Yamaha 3 cylinder - cross plane crank?

Dean15 wrote:
Remember the Laverda 1000 3-cylinder models of the 70's.

Some had 120 cranks, some had a flat crank with two up; one down. I can't think what the advantage of the latter arrangement might be.

Simples - they had a shed load of arsed up crank forgings, no point throwing them out, so grind the journals, tweek the timing and et voila - Robert's Your Mother's Brother!

Ciao

Dean15
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Re: Yamaha 3 cylinder - cross plane crank?

No, it can't be that simple. You'd need different camshafts.

Unless you believe they had a shedload of arsed-up camshaft blanks at the same time; now that would be spooky!

Mr Incredulous
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Re: Yamaha 3 cylinder - cross plane crank?

So what bike would they use this engine with, a new triple sport and naked to compete with Triumph and MV or maybe they have heard that a triple may be allowed into Moto2 ?

kevash
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Re: Yamaha 3 cylinder - cross plane crank?

Dean15 wrote:
No, it can't be that simple. You'd need different camshafts.

The camshaft blanks are all the same for the 120 and 180 degree cranks, it's just a case of resetting them on the grinding machines when the lobes are being formed. It really was that simple, Laverda, or rather its supplier, only had the resources to produce flat plane crankshafts, so that's what the first triples got! Then as the triples sold well, the supplier tooled up to make multiple plane cranks and the 120 degree versions came out.

kevash
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Re: Yamaha 3 cylinder - cross plane crank?

Mr Incredulous wrote:
So what bike would they use this engine with, a new triple sport and naked to compete with Triumph and MV or maybe they have heard that a triple may be allowed into Moto2 ?

They were suggesting the engine could be used in a wide range of bikes, so that's a yes to all of the above. The cross-plane layout is more advantageous in a sports bike but it can improve feel in any bike with a manual gearbox.

There's no reason why this shouldn't be a one litre superbike engine either, as well as a 675 or other capacity. The obvious first option is as an R6 replacement though, with associated naked Street Triple rival.

Dean15
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Re: Yamaha 3 cylinder - cross plane crank?

Thanks for that, Kevin. I've been puzzled since the 70's about the Jota's strange configuration, and at last it's been explained.

alanp
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Re: Yamaha 3 cylinder - cross plane crank?

Dean, the 180deg Laverda Jota crank sounded FABULOUS and when they went to 120 deg it lost its soul.
I can still recall my mates crowding around the rear of my 180deg Jota to listen to the exhaust....MAGIC.

Dean15
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Re: Yamaha 3 cylinder - cross plane crank?
shuggiemac
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Re: Yamaha 3 cylinder - cross plane crank?

Dean15 wrote:
No, it can't be that simple. You'd need different camshafts.

Unless you believe they had a shedload of arsed-up camshaft blanks at the same time; now that would be spooky!

I was being flippant but of course - cams came from the same place. It is 70's 80's Italy we are talking about !!! :-)

blacktiger
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Re: Yamaha 3 cylinder - cross plane crank?

Don't ya just love Yamaha? They really are THE innovators amongst the Jap manufacturers. I think they were first to shaft drive an across the frame 3 with the XS models. Off the wall bikes like the XZ550 and The V-max. Some don't sell well but at least they try. And here they go again. Brilliant.

alanp
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Re: Yamaha 3 cylinder - cross plane crank?

Dean15 wrote:
Alanp; yes, but did it vibrate?

Good article here:
http://www.motorcycleclassics.com/classic-italian-motorcycles/laverda-jota-1000.aspx


Vibration? I can't recall so maybe I was too absorbed by the sound to notice.
However, these days I need as little vibration as possible to stop my hands going numb.

pittsy
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Re: Yamaha 3 cylinder - cross plane crank?

Alanp said: "Vibration? I can't recall so maybe I was too absorbed by the sound to notice."

Hee Hee. Like your attitood. We were men in them days. Bit o rumbling thro the bars was all in the game.

Black tiger said: "Don't ya just love Yamaha? .........Off the wall bikes like the XZ550."

I like Yamaha, but not for that bike. It was rubbish. Rubbish handling. Rubbish performance. It was meant to be a CX beater but didn't come anywhere near it. I had both.

The xj550 was a good bit o kit tho.

IMO.

I agree with your basic idea though.

kevash
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Re: Yamaha 3 cylinder - cross plane crank?

@blacktiger: I think a lot of us have lost sight of that in recent years while Yamaha's been trying to hibernate through the recession, but it's great news that they want to return to those values - that's very specifically their aim. I'll putting together a feature about that, although there are also question marks about if they'll be able to achieve that, they're having some serious problems right now with more to come.

kevash
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Re: Yamaha 3 cylinder - cross plane crank?

Don't forget the GTS1000.... it didn't work as they'd hoped but it was brave and pioneering, and in Cologne they also said they're willing to go out and make mistakes again.

blacktiger
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Re: Yamaha 3 cylinder - cross plane crank?

kevash wrote:
Don't forget the GTS1000.... it didn't work as they'd hoped but it was brave and pioneering, and in Cologne they also said they're willing to go out and make mistakes again.

Well, IMO it would have worked if it wasn't sold at such a high price. That's one thing, in recent years, that Yamaha seem to be doing too much of. A lot of their bikes are just too expensive and are then sold off as old stock at the price they should have been in the first place. Maybe they should adopt the "stack 'em high, sell 'em cheap" mantra as lot's of smaller profits is better than one big one.

pittsy
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Re: Yamaha 3 cylinder - cross plane crank?

If the crank has 3 pins, arranged with a 90 degree spacing but leaving a final 180 degree spacing. Then if a dummy piston shared a pin if the dummy piston's axis was set at 90 degrees would this give zero inertial torque? I think the shared pin would have to not be the odd one. It could be either of the other two.

Don't know if that makes sense! It's probably total nonsense.

MoDa
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Re: Yamaha 3 cylinder - cross plane crank?

pittsy wrote:

The xj550 was a good bit o kit tho.
IMO.

Agree! And its younger sister the xj900, which after 23 years still faithfully brings me to my work every morning.

blacktiger
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Re: Yamaha 3 cylinder - cross plane crank?

pittsy wrote:

Black tiger said: "Don't ya just love Yamaha? .........Off the wall bikes like the XZ550."

I like Yamaha, but not for that bike. It was rubbish. Rubbish handling. Rubbish performance. It was meant to be a CX beater but didn't come anywhere near it. I had both.

The xj550 was a good bit o kit tho.

IMO.

I agree with your basic idea though.

So you were the bloke that bought "IT"? I mean the only one they sold. I never did see one on the road but for a while I thought it was the bike that suited my use the best at the time.
I just kept my XS750 a little longer and bought a 1983 XJ650YICS. That was a superb bike.

MoDa wrote:

Agree! And its younger sister the xj900, which after 23 years still faithfully brings me to my work every morning.

Changed the 650 for the 900S and wished I'd kept the 650 after a while. The 900 wasn't anywhere near as good as the 650. But, you know what? When I compare the performance of the XJ900S and my Tiger955i, they're almost identical. Power, torque, mpg, tank range, comfort. The Tiger handles better though.
Anyway, good to hear that Yamaha are experimenting again.

dunno58
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Re: Yamaha 3 cylinder - cross plane crank?

Kevin said: "I'm not convinced about this but it does explain some things. A conventional 120 degree triple does suffer from inertial torque fluctuation, not as bad as a flat plane four but a lot more than the near-zero of a cross-plane four like the R1 (or indeed a 90 degree V-twin)."

Not saying you are wrong, but can you how the 120 degree triple has inertial torque fluctuation? do you have a reference or something to link me to? As I said, not saying you are wrong but intuitively I would have thought a triple would't have this.

blacktiger
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Re: Yamaha 3 cylinder - cross plane crank?

dunno58 wrote:
Kevin said: "I'm not convinced about this but it does explain some things. A conventional 120 degree triple does suffer from inertial torque fluctuation, not as bad as a flat plane four but a lot more than the near-zero of a cross-plane four like the R1 (or indeed a 90 degree V-twin)."

Not saying you are wrong, but can you how the 120 degree triple has inertial torque fluctuation? do you have a reference or something to link me to? As I said, not saying you are wrong but intuitively I would have thought a triple would't have this.

Because you don't get one piston going up as another is coming down, exactly opposite each other. Therefore you don't get the cancelling forces that you do in a 4 X-plane crank.
What you get in a 120deg triple is, if you imagine one piston a TDC, the other two cancelling each other out but the one at TDC is stopped and needs energy to get going again.

dunno58
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Re: Yamaha 3 cylinder - cross plane crank?

blacktiger wrote:
dunno58 wrote:
Kevin said: "I'm not convinced about this but it does explain some things. A conventional 120 degree triple does suffer from inertial torque fluctuation, not as bad as a flat plane four but a lot more than the near-zero of a cross-plane four like the R1 (or indeed a 90 degree V-twin)."

Not saying you are wrong, but can you how the 120 degree triple has inertial torque fluctuation? do you have a reference or something to link me to? As I said, not saying you are wrong but intuitively I would have thought a triple would't have this.

Because you don't get one piston going up as another is coming down, exactly opposite each other. Therefore you don't get the cancelling forces that you do in a 4 X-plane crank.
What you get in a 120deg triple is, if you imagine one piston a TDC, the other two cancelling each other out but the one at TDC is stopped and needs energy to get going again.

Do the other two moving pistons not get it going again? Maybe thats what Kevin means by better than a flat plane 4 but not as good as a cross plane - the other 2 pistons help but dont go the whole way.

pittsy
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Re: Yamaha 3 cylinder - cross plane crank?

Black tiger said: "Because you don't get one piston going up as another is coming down, exactly opposite each other. Therefore you don't get the cancelling forces that you do in a 4 X-plane crank"

A flat plane gives you that, also. Surely?

Is it not the two crank pins at 90 and 270 deg which cancels out the inertial "brake" of the two crank pins at 0 and 180 deg?

Won't the 120 degree three provide some evening out of the inertial "brake" effect. Just not perfect.