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V-Twin 90 degree = harmonically balanced?

Discussion in '24-7 Lounge' started by Pspice, Mar 5, 2019.

  1. Pspice

    Pspice Just got it firing!

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    Hello forum,

    This is my first V-Twin motorcycle. I really like the vibrations coming from this engine.

    After several articles of reading I learned that 90 degree (and 180 degree?) V-Twins are inherently harmonically balanced which removes the primary vibrations, but secondary vibrations still remain. That said, I learned no counterbalancers are required as opposed to 45 or 60 degree v-twins. After my learnings, I have some questions:

    1. The Moto Guzzi V7 rocks side-to-side during idle (in-plane with pistons). Is this primary vibration?
    1a. If so, why does our moto guzzi v-twin have this much vibration if this is supposed to be naturally balanced?

    2. Secondary vibrations are vibrations that occur on a plane perpendicular to the primary vibration plane. Is this correct?

    After my readings on cycle world and other publications about v-twins, I'm just surprised that Moto Guzzi's V-Twin shakes and vibrates this much with its 90 degree angle.

    Is the Moto Guzzi 90 degree v-twin the smoothest operating V-Twin? If so, I can't imagine how much additional vibrations. I've never ridden a ducati but I would assume their 90 degree twin would vibrate equally the same as the Moto Guzzi v-twin?

    Anybody with knowledge about v-twins, feel free to educate me :)

    Thanks for the education!
     
  2. Kubbie

    Kubbie Tuned and Synch'ed

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    Rode a Ducati 996 yesterday.......... very similar vibration. Can't give you exact definitions of any of the movements.
    I've called the rocking sideways, especially when you blip the throttle, the torque reaction. Its caused by mass of the crank and pistons accelerating. All engines do it, just more noticeable on a M/G (or any bike with the crank running front to back) because of the smaller size of the bike.
     
  3. kiwi dave

    kiwi dave GT Reference

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    I've never understood this claim of natural balance. A boxer twin (a la BMW) has perfect primary balance as the forces of the two pistons (+rods & cranks) oppose each other exactly. With a 90° twin like a Guzzi or Ducati, only a portion has opposing primary balance.

    Yes. And that same boxer twin has more serious vibration as the pistons etc are much further apart, compared to a Guzzi whose big end bearings are adjacent to each other.


    It's a much more acceptable vibration IMHO. Try riding a solid engine mounted Harley or parallel twin like the Meridan Triumphs to feel real vibration.
     
  4. Kubbie

    Kubbie Tuned and Synch'ed

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    The Meridian twins? Pistons rise and fall together? Or opposite each other (one piston all the way up, the other all the way down)?
    My old KZ750 had 2 78mm pistons moving up and down together thru a 78mm stroke. Even with a balancer that thing vibrated.... A LOT!!!
     
  5. kiwi dave

    kiwi dave GT Reference

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    Meridan twins pistons did rise and fall together. They had the same balance as a single banger, i.e. none.

    Honda 350 & 450 twins were 180°, one up one down, it's questionable whether this arrangement created less vibration, I doubt it, there was also secondary vibration due to the rocking couple as per the BMW reference above.

    It was hard to compare as the motors were smaller than the bigger Triumphs I was riding way back then.
     
  6. Kubbie

    Kubbie Tuned and Synch'ed

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    Lol. Those bikes you mention were before my time.

    The KZ was my first street bike and was 15+ years old when I got it. Just had to look up the crankshaft on eBay to make sure I wasn't wrong about both pistons moving together (they do).
    But father-in-law has a 1970 BMW boxer that's mine if I even get round to buying it. And it has that same sideways rock.
     
  7. Knuckle Dragger

    Knuckle Dragger Just got it firing!

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    There's both reciprocating & rotating masses, and a bit of sideways 'chatter' from connecting rods too, that interact/cancel/accentuate each other. As for the twin cylinder vibes: would you REALLY want it any other way?

    PS the smoothest engines ever made are inline sixes (BMW's 2.0l six from early 3 & 5 series sedans are is perhaps the best of the best) & flat twelve boxer motors (really just 2 horizontally opposed straight sixes) such as Ferrari's old Berlinetta Boxer motor have perfect primary balance & are fabulously sweet, smooth, revvy, zingy motors. Everything else is, well..... a bit vibey in comparison.

    Don't care what physics dictates, ALL vee motors that I've ever encountered (twins, fours, fives, eights, tens, twelves, bike, car, industrial, marine & earth moving, petrol, diesel, bunker oil, 2-stroke, 4 stroke), irrespective of cylinder angles, have always had a lower frequency vibe characteristic.

    Parallel twins & inline fours & fives are always going to be a bit more high frequency 'buzzy'.

    PPS a lot of the idle rocking moment of longitudinal vees is down to the inertia of their reciprocating masses individually accelerating & decelerating through each of their 4-stroke cycles. A boxer motor will have self-cancelling (i.e. Newton's "equal & opposite reaction") moment/s of inertia.
     
    Last edited: Mar 6, 2019
  8. GuzziMoto

    GuzziMoto GT Reference GT Contributor

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    90 degree V twins have perfect primary balance but still have a fair amount of secondary imbalance. But the side to sige rocking motion has nothing to do with that. The rocking motion has to do with the motor rotating sideways and as the motor accelerates and / or decelerates there is a force in the opposite direction pushing on the engine block (that whole "for every action there is an equal and opposite reaction" thing). Clearly if you give it a bit of gas the motor rotates faster in one direction but it is doing so by pushing against the engine cases, which pushes them in the opposite direction. As the engine cases are firmly bolted to the bike the whole bike is moving in the other direction. But less obvious is that as the motor is spinning it is not doing so perfectly evenly. There are moments in the spinning of the engine where it is spinning a little faster and a little slower. Each of these tiny changes in the rate of spin also brings with it forces in the other direction. These changes in the rate of spin have to do with the fact that a combustion engine, unlike an electric motor, spins as a result of a series of events happening in sequence. Some of these events cause the motor to spin faster (the spark plug firing and igniting the air / fuel mixture) and some cause it to spin slower (compressing the air / fuel mixture prior to igniting it with the spark plug).
    Additionally, I don't think secondary vibrations are restricted to being 90 degrees to primary, I think they can be at other angles depending on the layout of the engine.
    The end result is that there are two aspects to our Moto Guzzi engines. One is that they are fairly vibration free compare to some other twins (like HD and old British twins) but they still have secondary vibrations. But that is separate from the side to side torquing of the motor that is more noticeable when you get on or off the gas but is always there. It is one of the things I first noticed when I road a Guzzi back in 1993, and it has always been something I enjoy.
     
  9. Pspice

    Pspice Just got it firing!

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    Really enjoying the feedback everyone is providing.

    In addition to side-to-side rocking during idle, I also understand the torque rev nature of longitudinal engines (blip throttle torques/tilt bike over just a bit) in cars and now I experience the same in my v7 racer.

    Before my v7 racer, I had a 2005 ninja250 (carburetor). While it had a mild high frequency low amplitude tingle, there was very little vibration when idling at 1000 rpm.

    This is my first v-twin and simply curious of the character; especially after some readings and in relation to my former ninja250 (parallel twin but I dont know if 360 or 180).
     
  10. GT-Rx®

    GT-Rx® Administrator Staff Member GT di Razza Pura

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    Congrats and welcome to the GT Forum and Guzzi Famiglia. Please post your info and VIN# on this thread if you would; https://www.guzzitech.com/forums/threads/v7-registry-picture-thread-add-your-bike.9108/

    Where in SoCal are you?
    Just asking because if you need help, service or almost anything, we are in the heart of SoCal; https://gtmotocycles.com/pages/service - or click the Service tab above at any time.
    We do a V7/V9 ride annually, and we often have meets and events in SoCal featured in this section; https://www.guzzitech.com/forums/forums/united-states-of-america.170/

    Hope you can meet up soon (once this rainy season clears!).
     
  11. Knuckle Dragger

    Knuckle Dragger Just got it firing!

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    There's some weird science going on here! Guzzi motors don't 'accelerate' or 'decelerate' to produce a rocking motion. The motor remains, as always, fairly rigidly fixed within the frame.

    The reciprocating (pistons, rings, gudgeons) & eccentric (connecting rods, crankshaft lobes) masses do their thing, accelerating & decelerating on their own individual planes & orbits, basically at a right angle of incidence to each other. There's no "equal & opposite reaction": sorry, my fault for quoting Newton's 3rd law, which was incidentally in specific reference to I-sixes & boxers only.

    Equal opposition occurs imperfectly in inline six cylinder & boxer motors. Imperfect because of course the individual piston planes of moment are offset from each other, spaced as they are along a common crankshaft. In horizontal boxer motors this introduces an inevitable additional lateral (i.e. horizontal) rotational moment: the offset reciprocating mass/es are trying to spin around their horizontal axis. In I-sixes the induced secondary rotational force is vertical. It's the inertia from these reciprocating & eccentrically rocking masses, the offset piston planes & angles of incidence, plus the product of internal friction, that creates longitudinal vee-twins' idling rocking characteristic.

    Those 1940's vintage marine & aircraft 2-stroke diesels with twin counter-rotating crank motors that had paired horizontally opposed pistons sharing a common cylinder bore with the combustion chamber cast into their crowns are the best example that I'm aware of that exemplifies the pure application of primary balance as it applies to Newton's 3rd law. The Junkers Jumo aircraft engine, Napier Deltic (triple crankshaft) marine & locomotive & the latest "OPOC" diesel from Advanced Propulsion Technologies are all more purist balanced designs. Especially as some are good for 20,000 hp (15 megaWatt) plus! An opposed piston engine would be much too wide for a bike I'd imagine. Anybody fancy a quad-crank, 24 cylinder, 48 piston rhomboid configuration 4,500 hp. supercharged 2 stroke diesel Jumo 224 scooter? Or maybe one powered by a Russian Zvesda M503 7-bank, 42 cylinder, 8000hp diesel radial motor? Still using that magical inline six configuration.

    The differences in the planes of moment are easily observed by comparing a boxer twin's motion. Boxers 'shimmy' at idle, whereas Gutsies (& CX Hondas) tend to shake.
     
    Last edited: Mar 6, 2019
  12. Pspice

    Pspice Just got it firing!

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    Hopefully, one day, I can be lucky enough to ride a ducati (90 degree L-twin) to compare the vibrational forces vs the moto guzzi 90 degree v-twin.

    I also just learned that the suzuki sv650 is also a 90 degree v-twin (or is it L-twin?), although liquid cooled. Hopefully I can experience that, too.

    Fun stuff!
     
  13. Knuckle Dragger

    Knuckle Dragger Just got it firing!

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    + Suzuki TL1000, plus the Honda something-or-other GCXL 3300 XLTQRSTUV. Both were pretty sub-standard wannabe Ducati imitations. Both missed the most characteristic aspect of Ducati engine manufacture, however: Desmodromic valve actuation & control.

    One of the sweetest automotive sounds of all time is that of an old-school (pre 1988) 750/900ss at idle. A veritable mechanical symphony of noise: the whine from the cam towers along each barrel driving the overhead valvetrain through bevel gears, the rhythmic mechanical double-speed counterpoint of desmodromic valve opening AND closing rocker clatter, the slurp & whoosh of each individual cylinder's air induction through unfiltered velocity stacks into a pair of 40mm Dell'Ortos, the menacing 'feel' of those big reciprocating pistons driving it all and the stunningly visceral subwoofer-like boom of escaping combustion byproducts through tuned-length La Fraconi or conical Conti trumpet "silencers". The sheer orgaistic bliss of an old Duke at idle is perhaps only bettered by the sound of on Imola Camshaft equipped one coming on song at around 6K RPM! It still gets me 'excited' just thinking about it!

    Gutsies may have character (& shakes) in spades. Old Dukes don't, or at least not in the same way. Their transverse crank layout prevents the more pronounced vibes of a big-block Gutsie, but what they DO have, unlike any other bike ever made (save maybe for an HRD Vincent) is an overwhelming ooze of innate sexuality from each & every pore, oil seal & orifice! The new (Pantah based) ones? Meh! I personally can't relate to these modern belt-drive wunderkinders. For me, as far as Ducati is concerned it's a stunningly mechanical bevel-drive geartrain or nothin'.
     
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  14. GuzziMoto

    GuzziMoto GT Reference GT Contributor

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    Sorry, but there is an equal and opposite force applied ANYTIME you apply force. It does not only apply to some engine configurations and not others. It always applies. And it is why when you rev a Guzzi at a stand still in neutral the engine as well as the motorcycle it is attached to will rotate in the opposite direction that the engine is rotating in.
    When a combustion engine rotating assembly rotates (as in when it is running) it does not rotate at a constant speed but rather it rotates with continual variations in speed as it speeds up and slows down during different phases of rotation. Try to use a timing light and you will see some evidence of the variation in rotating speed.
    The balance is different between a 90 degree V twing like a Guzzi engine and an opposed twin like a Boxer, so there is a difference in vibration. But both of them have the same rocking that occurs when you get on the gas and both will rock back and forth at idle.
     
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  15. Kubbie

    Kubbie Tuned and Synch'ed

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    It was Honda's Super Hawk and the RC51.
    Suzuki had the TL1000R and S before the SV.

    The term engine configuration made a conversation I had recently pop into my head.
    Guy comes up to me at our Sunday meet up. Pointed at the M/G and asked "what do they call that engine configuration?" With a very confused look on my face I said "V twin?. To be exact its a longitudinal 90° V twin!"
    Turns out he only saw the valve cover on the right side as he approached.
    Of course this got the guy on the Ducati going. "Hey, I have a 90° twin too.......
     
  16. Knuckle Dragger

    Knuckle Dragger Just got it firing!

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    Not quite sure what are you apologising for: paraphrasing what I just said?
     
    Last edited: Mar 27, 2019
  17. GuzziMoto

    GuzziMoto GT Reference GT Contributor

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    Just responding to this part of your post;
    "There's no "equal & opposite reaction""
     
  18. Knuckle Dragger

    Knuckle Dragger Just got it firing!

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    I'm obviously not communicating with sufficient succinctness.

    Individual pistons performing a basic Otto Cycle decelerate during their compression stroke, and accelerate during firing strokes. This inertia induces vibratory stresses & mass reactions in accordance with Newton's Third?? Law.

    Boxer motors have horizontally opposed banks of cylinders with phase motion similarity, but in opposition. The 'equal & opposite reaction' is balanced by the corresponding piston in the opposed bank doing the same thing but with a 180 degree phase difference, effectively cancelling (but never eliminating - impossible as it's an immutable law of physics) this reaction. Boxer motors are smoother than most and share with inline sixes the concept of 'perfect primary balance'. This doesn't stop them from vibrating, which is a product of their internal masses in motion. Due to pistons & connecting rods being not precisely opposed, but staggered along a linear crankshaft, they will also try to rotate back & forth around a theoretical vertical axis, and the accelerative & decelerative rotational inertia coupled with internal friction will simultaneously try to rotate the motor around a theoretical longitudinal axis too, at or near the rotative centre of the crankshaft.

    Vee motors have similar rotative moments to their horizontally opposed counterparts, but lack the boxers' perfect primary balance. The 180 degree phased opposed reaction to each bank of pistons' motion isn't present in a Vee motor. A Vee motor will consequently vibrate more as a product the out-of-phase action of each cylinder bank and their angular plane of moment in relation to each other.

    Any clearer now?
     
  19. GuzziMoto

    GuzziMoto GT Reference GT Contributor

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    In my opinion that was worded much better.
     
  20. scottmastrocinque

    scottmastrocinque High Miler GT Famiglia

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    There is a wealth of info here: https://en.wikipedia.org/wiki/Engine_balance#Rocking

    The tendency of the 90 degree V twin and Boxer engine to shake at idle and low speeds is caused by "rocking couple" which is discussed in the article. Rocking couple is minimized as speed of rotation increases.
     

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