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Parallel Twins crankshaft evolution: only KTM does it right?


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3 hours ago, GuzziMoto said:

To my knowledge, yes. The TRX Yamaha made, back in the mid 90's was the first mainstream offset crank parallel twin. Other brands like Honda had made offset cranks work for V twins, allowing them to get less vibration from narrow angle V twins. But the TRX was the first mainstream offset crank parallel twin as far as I know. The same engine also went into the TDM 850, which was already on sale with a 360 crank parallel twin. The 270 parallel twin was pretty much the 360 engine with a 270 crank and matching cams. I seem to recall there was a more cafe version of the TRX that never came here, but I could be wrong. I just seem to recall seeing a picture of one in white with a red trellis frame that was beautiful but never came to the USA. I wanted it.

So, the offset crank parallel twin has been around for near 3 decades. But it is surging in popularity right now. After Yamaha did it, there was really no one else for a long time. Yamaha took the same basic tech and made the Cross Plane R1 motor, but there wasn't much going on with Parallel twins for years. Everyone wanted a V twin despite the parallel twins better engine packaging. The sideways V twin on a Guzzi works well, but a proper 90 degree V twin that isn't sideways is very hard to properly fit in a compact motorcycle chassis. It clearly can be done, but it isn't always done right (see the TLR).

I also fell in love with the "Trixie." They are a cult bike elsewhere, still popular in Japan. The early models had oil consumption problems, which was the recall, if "I" recall correctly. I also looked at the more recent MT-07, which was the first wave of the new 270s. It was too much of a "transformer" style for me. The YZF-07 seems a rather nice bike, if slightly extreme for many "mature" riders. Yamaha is often odd-man out in engineering, trying all manner of new designs. In the 689 parallel twin, they moved the cylinder centerline forward in relation to the crank centerline. This gives the rod increased leverage over the crank as it fires. This changes crank angle at TDC, but they have dealt with that. But a piddling 65 BHP out of such a high-tech engine seems a waste, when 75-80 HP is available. Oh, well...

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On 1/27/2024 at 9:43 AM, p6x said:

 

This fellow, who does a lot of tech vids, disagrees on 285º parallel twins.

 

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On 2/4/2024 at 8:21 AM, po18guy said:

This fellow, who does a lot of tech vids, disagrees on 285º parallel twins.

 

That seems like a better technical video, with a better explanation of secondary forces with regard to engine balance. But he still missed one factor in secondary balance forces, the counterbalance weight on the crank. It is easier to think about this if you start by using a single cylinder engine as a baseline. Even a single cylinder engine has primary and secondary balance forces.

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I feel like I’ve got the best of both worlds with my TDM 900 (270 twin) and my V11. One is smooth, economical,  has linear power delivery and is generally a great bike for every day use, but doesn’t really excite. The other is the V11. A bit rough round the edges with its old school character and mechanics. It excites on every ride as you feel a part of it. The TDM has been under my care since 2005 and is just on 62k miles now, all done by me. The V11 since 2011 when I saw it and lusted after it. It’s the one I turn round to look at. 
 

I reckon it’s a pretty good pairing really. Performance is near identical between the two, but the delivery it totally different. They compliment each other nicely. 

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The everyday thing on the TDM isn’t boring by any stretch of the imagination. Having an Ohlins shock and upgraded cartridge fork internals ensures that. It’ll run rings around the V11 in the twisties. :D

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