21+ Valve timing changes?

[salishmoto]

Hi Folks,
We've had the 21 NC for almost a year now and continue to delight in the little thing. A technical question I wonder about is in the design of the new 21 engine that according to MCN: "With a rumbling 270˚ crank and different valve timing for each cylinder the Honda has plenty of feel. The first three gear ratios are lowered for sharper acceleration helping it to be the peppiest NC750X so far, feeling brisker than its modest numbers and limited rev range suggest." I understand ICE engines better than most, but am not an engineer. I don't understand how you can vary valve timing for each cylinder without negatively impacting the combustion process.

Presuming there is an optimum timing to maximize combustion, any retarding or accelerating of the timing would be less optimal, no? The engine has a throaty growl over 4K RPM and the 270 crank explains much or most of that. So what is the story of this valve timing change? How does that make sense from a mechanical perspective? VVT systems make sense because at different RPM's you can vary the timing to maximize combustion. But doing each cylinder of a two cylinder bike differently, when they are at the same RPM, defies my understanding. Any insights?

 

[670cc]

I’m convinced the simple answer is: there are no ‘21+ valve changes. The way the MCN statement is worded, it is open for misinterpretation. “With a rumbling 270˚ crank and different valve timing for each cylinder” is just that, and describes every NC ever made. The cam profiles for the two cylinders differ from one another.. Furthermore, this is the same way it was from the beginning, in the 2012 700. As far as this article goes and from what I know, there is nothing going on in the ‘21 valves that wasn’t already going on at NC day one. Rather it sounds like the modern day journalists were just grabbing at news release bullet points to make the ‘21 sound sensational.

If you go find a 2012 introductory technical paper, it explains it. If I remember correctly, it’s because this engine has two cylinders sharing one intake path with an uneven firing order. The single throttle body delivers to the head as one intake, and air to the two cylinders is split within the head. But, because the intake strokes are not evenly timed, the two cylinders tended to get uneven charges, perhaps something like the first guy getting more than the guy that follows. So, the cam timing for each cylinder differs slightly to compensate for this problem, so that the two cylinders end up producing the same ”strength” power pulse. Again, Honda documents from 2012 explained this design element.

You’ll see it mentioned in the 7th paragraph of this July, 2012 article: https://www.ashonbikes.com/content/honda-nc700x

By the way, I don’t want to read anyone repeating that “half a Jazz” joke, because it is nothing more than that, just a joke.

 

[salishmoto]

I'm no expert but numerous publications speak of changes to the timing in the 21 and later models. You have very strong feelings on the subject, 670cc, and that's fine, but I remain curious why it is mentioned so often in written and video reviews. This is from ultimate motorcycling:

1. The motor and transmission have been altered for improved acceleration and top-end power. New valve timing and exhaust system pump up torque above 5000 rpm to the 7000 rpm rev limit. To boost lower-speed acceleration, 1st, 2nd, and 3rd gears are all lower. Put those changes together, and the 2021 Honda NC750X feels noticeably sportier in both urban and rural settings. Honda retained the burbling feel and torquey performance that comes with the 270-degree crank firing. Like the frame, the motor shed 2.6 pounds.

It is hard to believe the publications are just making this crap up.

 

[jeremyr62]

It's just marketing guff. They have to write something. For the end user in terms of maintenance there will be no impact.

 

[NE-Okie]

On the lighter side this may be a way of selling an unlikely senero where they have some hillbilly like myself making cam shafts and not one is the same as any other. However, most of them can be sorted out into 21 various categories.

 

[dduelin]

I'm no expert but numerous publications speak of changes to the timing in the 21 and later models. You have very strong feelings on the subject, 670cc, and that's fine, but I remain curious why it is mentioned so often in written and video reviews. This is from ultimate motorcycling:

1. The motor and transmission have been altered for improved acceleration and top-end power. New valve timing and exhaust system pump up torque above 5000 rpm to the 7000 rpm rev limit. To boost lower-speed acceleration, 1st, 2nd, and 3rd gears are all lower. Put those changes together, and the 2021 Honda NC750X feels noticeably sportier in both urban and rural settings. Honda retained the burbling feel and torquey performance that comes with the 270-degree crank firing. Like the frame, the motor shed 2.6 pounds.

It is hard to believe the publications are just making this crap up.

Numerous publications parrot the crap, er, bullet points in the press release package handed or emailed to them by Honda. That's what they do and is exactly what the manufacturer wants them to do. Do you think each journalist researched the valve timing of each NC700/750 model for 10 years in order to come up with this realization on his/her own? There may well have been subtle valve timing changes in the '21 engine but since it's inception the NC's parallel twin has had different valve timing for each cylinder. In initial technical descriptions of the New Concept engine Honda says it's for two reasons. One, the engine shares a common intake tract instead of the more common separate tract for each cylinder. The firing order of a 270 degree crankshaft causes uneven pressure waves in the tract that interfere with precise combustion in each cylinder so each cylinder got it's own cam profile to optimize combustion efficiency despite pressure wave interference between cylinders. Secondly, Honda supposedly tuned the valve timing to promote subtle variations in engine vibration and give the engine some character. Apparently there was too much character as the second generation NC engine got a second counter balancer, the first gen NC has just one, to help smooth out the pulsing vibration inherent in a 270 degree firing order. The valve timing may have been altered in the 745cc version to reduce the "subtle variations" the engineers desired in the original 670cc motor.

 

[670cc]

I'm no expert but numerous publications speak of changes to the timing in the 21 and later models. You have very strong feelings on the subject, 670cc, and that's fine, but I remain curious why it is mentioned so often in written and video reviews. This is from ultimate motorcycling:

1. The motor and transmission have been altered for improved acceleration and top-end power. New valve timing and exhaust system pump up torque above 5000 rpm to the 7000 rpm rev limit. To boost lower-speed acceleration, 1st, 2nd, and 3rd gears are all lower. Put those changes together, and the 2021 Honda NC750X feels noticeably sportier in both urban and rural settings. Honda retained the burbling feel and torquey performance that comes with the 270-degree crank firing. Like the frame, the motor shed 2.6 pounds.

It is hard to believe the publications are just making this crap up.

I’m totally open to the idea that the ‘21 valve timing has been altered to change engine output characteristics, but where are the details? Maybe ultimate motorcycling and MCN were handed the same packets but focused on different features. MCN apparently liked the part about the valve timing difference from cylinder to cylinder. The original post is questioning that unequal valve time aspect, and I responded to that concern.

Again, all the public needs is some details, like maybe describe the cam timing changes in degrees, or display the power curve charts from pre- ‘21 and ‘21, from the same tester/ same instrument. I‘ve seen so much rubbish come from moto journalists, and careful wordplay from Honda, so I’m naturally skeptical of marketing announcements.

 

[salishmoto]

I'm glad to hear thoughts from people and have learned things here. No doubt about marketing hype and all that. Having not ridden a pre-21, that would be a good test. I've had other twins, including a parallel twin in the Versys 650, and there is no doubt this 21 is much more rumbly and throaty than that. Much more like my Aprilia Caponord had been with a V-twin.

Having a single inlet as several here describe does go some way in explaining the rationale of varying timing. And I don't believe anyone has pointed out the simple truth that these bikes are not engineered for max HP anyway. Sacrificing some amount of "optimum" burn may be less important, although fuel economy would suffer with incomplete burns and that can't be much the case with the NC. My other bike right now is an S1000XR, and it's a great contrast to how with only 250CC more engine space, you get more than 100 more HP, based on nothing more than stroke, compression, valve timing and the variables ICE engineers can play with. Amazing.

 

[dduelin]

…., And I don't believe anyone has pointed out the simple truth that these bikes are not engineered for max HP anyway….

Only about 100 times usually in reply to a post wondering how to uncork the NC motor.

 

[jeremyr62]

My other bike right now is an S1000XR, and it's a great contrast to how with only 250CC more engine space, you get more than 100 more HP

I had a GSXR750K7 and I did a GPS verified 253km/h on that (in Germany of course) a long time ago when I was stupid. My NC750S will barely reach 165km/h. Still, its a great bike for what it is.

 

[salishmoto]

Only about 100 times usually in reply to a post wondering how to uncork the NC motor.

True enough generally, but I was referring to in this thread...

 

[MartiJ]

Having a single inlet as several here describe does go some way in explaining the rationale of varying timing. And I don't believe anyone has pointed out the simple truth that these bikes are not engineered for max HP anyway. Sacrificing some amount of "optimum" burn may be less important, although fuel economy would suffer with incomplete burns and that can't be much the case with the NC. My other bike right now is an S1000XR, and it's a great contrast to how with only 250CC more engine space, you get more than 100 more HP, based on nothing more than stroke, compression, valve timing and the variables ICE engineers can play with. Amazing.

Here is an old interview with the NC designer on what they were striving to create.

NC Project leader Soya Uchida

 

[670cc]

I'm no expert but numerous publications speak of changes to the timing in the 21 and later models. You have very strong feelings on the subject, 670cc, and that's fine, but I remain curious why it is mentioned so often in written and video reviews. This is from ultimate motorcycling:

1. The motor and transmission have been altered for improved acceleration and top-end power. New valve timing and exhaust system pump up torque above 5000 rpm to the 7000 rpm rev limit. To boost lower-speed acceleration, 1st, 2nd, and 3rd gears are all lower. Put those changes together, and the 2021 Honda NC750X feels noticeably sportier in both urban and rural settings. Honda retained the burbling feel and torquey performance that comes with the 270-degree crank firing. Like the frame, the motor shed 2.6 pounds.

It is hard to believe the publications are just making this crap up.

You can’t help but see the primary motojournalist point of view on display here. The article speaks in terms of acceleration, top-end, power, sportier, and performance, none of which were really the main goal in the NC’s design. Motojournalists just don’t get it, and never will. Sadly, I see the days of the New Concept slowly coming to an end, as Honda’s changes to the NC since it’s beginning have been mainly towards power enhancement, not really towards greater efficiency. However it does still have real world usability as a primary attribute.

 

[salishmoto]

I've learned things in this thread, and that's awesome. One thing I've reflected on is that in my fairly extensive experience on bike forums, spanning many bikes from most every major manufacturer, it is a peculiarity of the NC forum to have a distinctly contrary or antagonistic relationship with the journalists who cover the bike. I think I understand why, it's just really apparent. No such discussions happen at all, or with any frequency, on the forums of more mainstream bikes like my Connie, FJR, Guzzi's, BMW, Tracer 9, Aprilia. The article @MartiJ linked to was fantastic, and I'm sorry to learn of that journalists death.

 

[670cc]

I've learned things in this thread, and that's awesome. One thing I've reflected on is that in my fairly extensive experience on bike forums, spanning many bikes from most every major manufacturer, it is a peculiarity of the NC forum to have a distinctly contrary or antagonistic relationship with the journalists who cover the bike. I think I understand why, it's just really apparent. No such discussions happen at all, or with any frequency, on the forums of more mainstream bikes like my Connie, FJR, Guzzi's, BMW, Tracer 9, Aprilia. The article @MartiJ linked to was fantastic, and I'm sorry to learn of that journalists death.

Yes, the NC was/is a rather unique motorcycle and testers/reviewers couldn’t/can’t seem to get out of their sport bike or cruiser box and test the bike on it’s own terms. Kevin Ash was an exception.

 

[dduelin]

Here is an old interview with the NC designer on what they were striving to create.

NC Project leader Soya Uchida

The Ash On Bikes review was linked in post #2 above.

 

[jeremyr62]

I'm sorry to learn of that journalists death.

I was at University with Kevin Ash. That was Imperial College in London. He had been studying Mech Eng, but by the time I got to know him in the Uni motorcycle club he had left the course. It was pretty clear even back then he was going to be some kind of journalist. He was a mine of information. He was very highly regarded in the UK bike press.

 

[dduelin]

As owners we (I) do tend to focus on negative or superficial journalistically "lazy" reviews but to be fair there have been some positive and insightful reviews of the NC700/750. I began collecting information and reviews of this bike in the spring of 2012 and putting them in a binder. With the last review I collected, the 2017 issue of RIDER, the content of my binder approached 200 pages. I should add some articles on the 2021 model specifically the March 2022 issue of CYCLE WORLD should in my binder. Early on the British magazine BIKE did some insightful pieces on the bike and ultimately chose the NC700X as their 2012 Bike of The Year. The first CYCLE WORLD ride review from the world press release in late 2011 was positive as was the CANADIAN MOTO GUIDE online article in early 2012. CYCLE WORLD'S editorial writer Mark Tuttle wrote a November 2012 editorial "Paradigm Shift" on the bike and on DCT and while he concluded the bike wasn't something he wanted in his garage if he only had one bike he noted the reasons it could be the choice of other riders. The same issue's in depth review was penned by Tuttle and came across as very fair. To round things out Tuttle wrote another balanced review of the then newly refreshed 2016 model in March that year after an 800 mile touring ride on a DCT. The US version of MCN did two positive reviews of the bike in 2012. RIDE APART did an off-beat article in 2013 that took a manual on an off road 700 mile predominantly high speed event called Taste of Dakar staged in the loose soil and rocks of the Nevada desert. Only equipped with a set of TKC 80s the 700X went everywhere and up every hill the other bikes did. Other bikes on the event weekend were dedicated dual sports like the DR-Z400 and big adventure bikes like BMW GSs.

What I see from this perspective is that some of the initial mistakes that came out of the initial in-person media event in 2011 that released the bike to the world press have been propagated over and over again in subsequent reviews. Whether Honda made these mistakes in press release packages or journalists made them during the in-person interview with Honda engineer Soya Uchida in Portugal they linger on in subsequent reviews and forum posts after a decade. I'm speaking to the Half A Jazz (Fit) engine origins of the motor, linked ABS brakes supposedly offered on post 2013 bikes, the 47.5 hp engine supplied with DCT bikes and 51.7 hp engine supplied with 6 speed manual transmission models. It isn't, they weren't, and all US bikes regardless of transmission fitted came with the 51.7 hp engine.

 

[jeremyr62]

Can't disagree. Most of the reviews I have read over the years have been broadly positive.
Any real motorcyclist knows anything with two wheels and and an engine is a good thing. In my experience a lot the criticism of the NC comes from wannabees who don't even ride, but in their heads would only be seen on a 200hp superbike (when they have passed their test which will probably be never).

 

[dduelin]

Can't disagree. Most of the reviews I have read over the years have been broadly positive.
Any real motorcyclist knows anything with two wheels and and an engine is a good thing. In my experience a lot the criticism of the NC comes from wannabees who don't even ride, but in their heads would only be seen on a 200hp superbike (when they have passed their test which will probably be never).

Post review comments and online motorcycle forum comments over 10 years follow your sentiments pretty closely. In the beginning there were a few people that thought a bike like the low priced NC was going to bring in new motorcyclists and be good for the sport but many self identified riders dismissed it, sometimes brutally. That was OK because they weren't the riders in Honda's target demographic. As an experienced rider in 2012 I did not fit the new rider demographic but I was looking for an easy to live with 50 hp motorcycle that was budget priced and promised low operating costs and could be seen filling diverse roles. It was just what I was looking for to add to the bikes I owned but not as the only bike in my garage. Where I think things went wrong is that motorcycle salesmen were often made up of riders looking for traditional 'power, excitement, and more of it' associated with riding in the USA. If a dealer even ordered one it might well have sat in a corner of the showroom gathering dust.