New F4 balance shaft - MVAgusta.net
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post #1 of 13 (permalink) Old 01-04-2010, 01:40 PM Thread Starter
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New F4 balance shaft

Having seen the new F4 you can see that MV have addressed all the problems that the old bike has had for the last 10 years, however the one thing I can't understand is why does the new F4 have a balance shaft? I haven't had any problems with vibrations with the old F4s and I can't say that I have ever read any bad reports in the press saying that the old F4 vibrated. Any ideas
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post #2 of 13 (permalink) Old 01-04-2010, 01:45 PM
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Originally Posted by stephen wood View Post
Having seen the new F4 you can see that MV have addressed all the problems that the old bike has had for the last 10 years, however the one thing I can't understand is why does the new F4 have a balance shaft? I haven't had any problems with vibrations with the old F4s and I can't say that I have ever read any bad reports in the press saying that the old F4 vibrated. Any ideas
Mine vibrates the bars (right more than left) right at 5-6K rpm which is pretty hand numbing at freeway drone.
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post #3 of 13 (permalink) Old 01-04-2010, 02:00 PM
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post #4 of 13 (permalink) Old 01-04-2010, 03:12 PM
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Vibration? In an F4? Go ride a hardtail Harley and tell me how an F4 vibrates.
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post #5 of 13 (permalink) Old 01-04-2010, 03:31 PM
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The couple of roadtests I read in Australian Motor Cycle News noted that in comparison to the Japanese in line 4 cylinders, the MV vibrated quite badly - especially in the upper rev range.

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post #6 of 13 (permalink) Old 01-04-2010, 03:39 PM
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I think some vibrate more than others, my 3 were fine, some 910 Brutales vibrate, one lad needed his crank balancing on an F4 because it was that bad, Mitsubishi Evo's have two balancer shafts, and apparantly so do in line 4 Suzuki's, The 4 cylinder engine has no 'natural balance' see below:

Balance shafts are most common in inline four cylinder engines which, due to the asymmetry of their design, have an inherent second order vibration (vibrating at twice the engine RPM) which cannot be eliminated no matter how well the internal components are balanced. Flat engines have their pistons horizontally opposed, so they are naturally balanced and do not incur the extra complexity, cost or power loss associated with balance shafts. This vibration is generated because the movement of the connecting rods in an inline engine is not symmetrical throughout the crankshaft rotation; thus during a given period of crankshaft rotation, the descending and ascending pistons are not always completely opposed in their acceleration, giving rise to a net vertical inertial force twice in each revolution whose intensity increases quadratically with RPM, no matter how closely the components are matched for weight.[2]

The problem increases with larger engine displacement, since the only ways to achieve larger displacement are with a longer piston stroke, increasing the difference in acceleration, or by a larger bore, increasing the mass of the pistons; either way, the magnitude of the inertial vibration increases. For many years, two litres was viewed as the 'unofficial' displacement limit for a production inline four-cylinder engine with acceptable NVH characteristics.

The basic concept has a pair of balance shafts rotating in opposite directions at twice the engine speed. Equally-sized eccentric weights on these shafts are sized and phased so that the inertial reaction to their counter-rotation cancels out in the horizontal plane, but adds in the vertical plane, giving a net force equal to but 180 degrees out-of-phase with the undesired second-order vibration of the basic engine, thereby canceling it. The actual implementation of the concept, however, is concrete enough to be patented. The basic problem presented by the concept is adequately supporting and lubricating a part rotating at twice engine speed where the second order vibration becomes unacceptable.

There is some debate as to how much power the twin balance shafts cost the engine. The basic figure given is usually around 15 hp (11 kW), but this may be excessive for pure friction losses. It is possible that this is a miscalculation derived from the common use of an inertial dynamometer, which calculates power from angular acceleration rather than actual measurement of steady state torque. The 15 hp (11 kW), then, includes both the actual frictional loss as well as the increase in angular inertia of the rapidly rotating shafts, which would not be a factor at steady speed. Nevertheless, some owners modify their engines by removing the balance shafts, both to reclaim some of this power and to reduce complexity and potential areas of breakage for high performance and racing use, as it is commonly (but falsely) believed that the smoothness provided by the balance shafts can be attained after their removal by careful balancing of the reciprocating components of the engine.[citation needed]

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post #7 of 13 (permalink) Old 01-04-2010, 03:50 PM
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Quote:
Originally Posted by stephen wood View Post
Having seen the new F4 you can see that MV have addressed all the problems that the old bike has had for the last 10 years
I think it's fair to say we can see the biggest problems (heat, bearings (new design spoken of), any others my early morning mind can't think of now?) have been addressed; however we can only hope at this stage, rectified.

Also I'm interested to see if new problems have been introduced. I wouldn't want to buy the first one
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post #8 of 13 (permalink) Old 01-04-2010, 04:52 PM
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Big bore Suzuki I-4s have a single balancer. Suzuki doesn't use one in the GSX-R600 bike, although the space is available in the cases, because the design sharing 750 does have one.

I will opine that the original MV F4 750 engine did not need a balancer, but as the engine grew the potential for vibration did as well. This is the first opportunity to add a balancer as new crankcases were being designed.

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post #9 of 13 (permalink) Old 01-04-2010, 04:55 PM
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If I remember right from my visit to the factory and EICMA during November, the new F4 does NOT have a balancing shaft.
The new Brutales do, but not the F4.
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post #10 of 13 (permalink) Old 01-04-2010, 05:45 PM
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Originally Posted by frenaugo View Post
Mike, not meaning to high-jack your post,,

If anyone is interested in further reading on this, there's loads of info about this and more here http://dinamoto.it/

go to 'papers on-line'
'Hi Jack' away the stuff I posted was just a quick copy and paste from Wikapedia I think

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Previously (and about 40 others)748SP, S4, S4R, 98R1, 2000 F4, F41000S, F41000R, 08R1, 09R1, S1000RR, RSV4 Factory aPRC in Garage now
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