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Thread: (Nc700) characteristics of a 270 degree parallel twin.

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    (Nc700) characteristics of a 270 degree parallel twin.

    What are the characteristics of a the 270 degree parallel twin in terms of engine sound, vibration etc. I have a 2015 nc700 that's going in for its first 600 mile service. I bought it brand new. I had a bit of a concern that the engine had a clackity clack, almost piston slap(ish) sound at idle. I took it in and they listened and said it was just the character of the 270 degree engine. They even pulled another one off the floor and started it up.

  2. #2
    Super Moderator (Nc700) characteristics of a 270 degree parallel twin. 670cc's Avatar
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    It's my understanding that the 270 degree parallel twin mimics a 90 degree v twin in terms of firing order. I don't see how that would relate to any piston slap noise. The clackity clack is probably the valves. If they're a bit noisy, that's good.

    To be honest, we have 8 motorcycles and I couldn't tell you if any of them do or don't sound "normal." I just put in earplugs and go ride. They all work fine and last a long time. I wouldn't worry about it. Go ride.
    Greg
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  3. #3
    Senior Member Jt105's Avatar
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    Some say that 270 degree firing order gives a more appealing vibration than 360 or 180.



    The 270 feels like it is running smooth, but has a subtle gallop that is almost imperceptible. Itís kinda like your favorite song that has a nice drum track with that little up-beat hit that just makes it sound right.

    None of these firing orders have anything to do with clatter noise. The clackety-clack is how the mechanical valves were designed. It is also more noticeable since the engine runs at a lower, thumping rpm. The ears and brain can pick up on more of the individual tickety-ticks.

    JT

  4. #4
    Senior Member (Nc700) characteristics of a 270 degree parallel twin. dduelin's Avatar
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    Speaking blindly but to a familiar recurring subject in this forum........... The NC spends much of it's time in the lower rev range of motorcycle engine rpm, say 1800 to 4000 rpm. Coupled with the 270 degree off beat Bang Bang Long Pause Bang Bang firing cycle (see the above post) this motorcycle can feel like it's not running right with a lumpy type of pulsing vibration at lower rpms. This engine also has subtle intake timing differences between cylinders that contribute to the pulsing sort of throb that is entirely normal.

    Many motorcycles have valve actuators that act directly on the valve while others like the NC have a mechanism that uses a lever of sorts to press the valve open. The former are very quiet in operation and the latter, like the NC, are characterized by tapping or clacking when the valves are pressed open and closed by the valve follower.

    In short, this engine does vibrate a bit under load and makes clattering noises. I for one like the soft pulsing vibration at cruising rpms and liken it to a gallop or cadence that JT105 mentioned in the prior post.
    Dave

    GL1800
    NC700XD




  5. #5
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    The other engine character noise of the NC that consistently comes up .........is the clutch, primary drive and transmission.
    Pull in the clutch at idle the engine noise level changes a considerable amount.

  6. #6
    Senior Member (Nc700) characteristics of a 270 degree parallel twin.
    (Nc700) characteristics of a 270 degree parallel twin.
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    You guys have posted about the best explanation of firing order and the various effects that I’ve ever seen.


    Iím supposed to respect my elders, but itís getting harder and harder for me to find one now ..

  7. #7
    Senior Member Rapturee's Avatar
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    YAH, what he said! :{)
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  8. #8
    Senior Member Griff's Avatar
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    Yep I agree with all said above, they can be rattly and somewhat noisy at times and other times quiet. These engines have many unique sounds including the sucking sound from the air box when cold on startup, and the metallic whistle from said airbox at times under full throttle. All such sounds have been analysed and put to bed over the past 6/7 years. As with any motor, You will know a really bad sound if you hear it. With these motors that is highly unlikely and there are very big mileages on some of them out there with no issues. That 270 crank plus the undersquare cylinder dimensions were a major factor in my having one of these brilliant bikes albeit mine is a variant and my second one to date.
    It's never too late to have a happy childhood.

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    Early twins used the 360 arrangement, but counter balanceers used to reduce up/down vibration then created forward and backwards vibration.

    Using the 270 arrangement, reduces the vibration intensity since the pistons aren't reaching the top or bottom at the same time.
    This lets manufacturers use smaller counter balancers, and it supposedly helps with traction.

    The NC's flattened engine layout makes the up/down vibration more forwards/backwards.
    I'm guessing this has some impact on perceived vibration, but I wouldn't bet money on that.

    New BMW's using the 360 firing arrangement, use a counter weight held that just goes up and down opposite the pistons, countering the up and down motion of the pistons without adding forward, and backwards vibration. The counter weight is kept from rotating with an arm, and a couple bearings.

  10. #10
    Junior Member mr_et2's Avatar
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    Glad I found this thread before I started typing, lol. I was about to ask about the vibrations this bike gives out. It's definitely a different feel than what I'm used to with single cylinder and older Honda twins, but so far I'm really loving my NCX. Got 85 miles on her now... now if it would only stop raining and stay above 60 out...

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