Vibration in grips at 3k-5k RPM...any way to correct?

[audiomick]

Dunno about a "sweet spot", but Ernst (who really does know what he is talking about, far more than me....) mentioned a crucial point.

He suspected con rods heavier than spec. You wrote about having changed the pistons. Both of those (can) mess up the balance of the motor, and make it vibrate (and in the worst case, self destruct.).

As far as the conrods go, if one were to suspect that as an issue, one would have to find out the correct weight and weigh the ones in the motor.

As far as swapping the pistons goes, I would weigh the old ones and the new ones. If there is any difference, the crank should be re-balanced (as far as I know). Same goes for swapping the conrods...

[GuzziMoto]

The drop in pistons are supposed to be the same weight as the originals, but have higher compression.

If your piston weight changes, or the piston and / or rods are not the correct weight, you certainly can run into vibration issues. I am not sure that Guzzi built motors with connecting rods that were the wrong weight (lighter or heavier, either one would vibrate). But it is certainly possible. It is also possible that they simply did not properly balance some engines.

Vibration can be caused by balance issues. Or it can be caused by tuning issues (the two cylinders not running evenly).

[Joe]

The Fast by Feracci domed pistons were the same weight just higher compression (domed), installed by a top notch motorcycle mechanic. My point was that you can over tune a bike w higher compression and map it to make the bike faster but at the cost of more vibration.

https://www.ferracci.com/products/piston-kit-92mm-11-1-v11-sport-lemans

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Fast by Ferracci

Moto Guzzi - PISTON KIT - 92mm CR 11:1 V11 Sport/Le Mans code F27700   $589.95 Regular price$900.90

[Pressureangle]

In my (now Son's) '85 LeMans, I installed Carrillo rods, cut the heads .010", and installed a Web 85b cam. 

It's dead smooth compared to stock, at any RPM. 

The lesson here, of which I have many examples, is that 'engine balance' and especially 'factory balance' are theoretical models coupled with testing to achieve a target RPM at which the engine is smoothest. If you ride outside the bell curve of balance, or you like the higher and and your particular engine tolerance stacks to balance at a slightly lower RPM you get more buzz. So then let me state for the record that piston weight is not any sort of structural threat, and only affects balance in a small way- sometimes making it better, sometimes making it worse. 
Flat track engines (back in my day anyway ) were often balanced to a factor of 100%, which kept all the vibration in the horizontal plane, with the claim that it helped traction. Certainly, at very high RPM in lightweight solid mounted frames it kept felt vibration way down, which was probably of more benefit than any claim to traction. This is sort of rambling, but balancing engines which are not used to the margin of their structure is simply a matter of comfort. 

[Joe]

3 minutes ago, Pressureangle said:

In my (now Son's) '85 LeMans, I installed Carrillo rods, cut the heads .010", and installed a Web 85b cam. 

It's dead smooth compared to stock, at any RPM. 

The lesson here, of which I have many examples, is that 'engine balance' and especially 'factory balance' are theoretical models coupled with testing to achieve a target RPM at which the engine is smoothest. If you ride outside the bell curve of balance, or you like the higher and and your particular engine tolerance stacks to balance at a slightly lower RPM you get more buzz. So then let me state for the record that piston weight is not any sort of structural threat, and only affects balance in a small way- sometimes making it better, sometimes making it worse. 
Flat track engines (back in my day anyway ) were often balanced to a factor of 100%, which kept all the vibration in the horizontal plane, with the claim that it helped traction. Certainly, at very high RPM in lightweight solid mounted frames it kept felt vibration way down, which was probably of more benefit than any claim to traction. This is sort of rambling, but balancing engines which are not used to the margin of their structure is simply a matter of comfort. 

Brilliant answer, thank you Eric! Aka Forum Elite Mechanic.

[Pressureangle]

5 hours ago, Joe said:

Brilliant answer, thank you Eric! Aka Forum Elite Mechanic.

It's true, I've had many more failures than the average.

[docc]

6 hours ago, Joe said:

Brilliant answer, thank you Eric! Aka Forum Elite Mechanic.

 

24 minutes ago, Pressureangle said:

It's true, I've had many more failures than the average.

Hey! I resemble that remark!

[motoguzznix]

14 hours ago, Pressureangle said:

In my (now Son's) '85 LeMans, I installed Carrillo rods, cut the heads .010", and installed a Web 85b cam. 

It's dead smooth compared to stock, at any RPM. 

The lesson here, of which I have many examples, is that 'engine balance' and especially 'factory balance' are theoretical models coupled with testing to achieve a target RPM at which the engine is smoothest. If you ride outside the bell curve of balance, or you like the higher and and your particular engine tolerance stacks to balance at a slightly lower RPM you get more buzz.

Sorry when I s´disagree in this respect,

Balancing has no sweet spot. When your tire is out of balance, it will get worse the faster you drive. The same goes for the piston/rod/crank balance. 

Best example is your engine mentioned above: dead smooth at any rpm. If your engine was not balanced, then you were lucky to get the right parts together. The carillos are a lot lighter at the bottom end than standard rods which may contribute to the smooth engine. 

[motoguzznix]

18 hours ago, Joe said:

I owned a 2001 Silver V11 Sport new that I later added a Fast by Ferracci drop in pistons, FBF Power Commander w a custom map made to make peak horsepower, lastly FBF carbon exhausts. We also created a vibration machine that even with Throttle Meister heavy bar end weights couldn't resolve, leaving you with numbness on demand.

Hey Joe

From my point of view this engine was missing some measures necessary:

The hi comp pistons with a CR of 11:1 are over the top for a V11 in my opinion. The piston dome is higher, thus the compression chamber shape gets worse. And note: The big valve heads like in the V11 still have the worst combustion chamber shape of all Guzzi heads. The best solution to overcome this problem ist installing twin spark ignition which shortens the time to burn the air/fuel mixture. The Guzzi engineers invented this  when they created the Breva engine.

This leads us to the ignition map: The V11 has extremely high ignition advance figures. At max rpm and WOT the advance is 44° which works only with the low VE the standard engine generates. When you increase the pressure in the combustion chamber by either aspirating more air into or a higher CR, the engine burns the mixture faster which allows us to reduce iginition adance. 

The same goes for the twin spark: the mixture burns faster, ignition avance can be reduced. 

A PC can only address the mixture, with an appropriate ignition map your engine would have beeen performing a lot better, be it power or vibration level. 

The graph below shows the influence of ignition advance on power and torque on my own V11. The only difference between the two measurements is for the red curve ignition advance was reduced by 3° at full throttle which indicates the stock advance figures were over the top.

[Pressureangle]

1 hour ago, motoguzznix said:

Sorry when I s´disagree in this respect,

Balancing has no sweet spot. When your tire is out of balance, it will get worse the faster you drive. The same goes for the piston/rod/crank balance. 

Best example is your engine mentioned above: dead smooth at any rpm. If your engine was not balanced, then you were lucky to get the right parts together. The carillos are a lot lighter at the bottom end than standard rods which may contribute to the smooth engine. 

Correct of course, but you've missed the point. It's not the engine we're concerned with, but the handlebars and footpegs and seat. These things have resonant frequencies, and riding with engine RPM in those resonant ranges is uncomfortable. Changing balance factors can uncouple resonant auxilliaries. My carrillo engine is not smoother because it shakes less, but because it isn't felt in the frame and controls. 
Vibration energy is a function of crankshaft rotating weight, which tries to drag the engine cases with it in a circle. The weight of the reciprocating parts counteracts that even, circular pull but only in the plane of the cylinder; The median balance factor is 50% (that is, crank counterweight is 50% of reciprocating) which then reverses the rotation of the crank action against the cases and minimizes the peak energy at any given direction. A 100% balance factor ends vertical shake (for vertical cylinders) but then the horizontal peak has become twice as energetic. 
I suspect you know most of this already but it's clarity in the classroom. 

[al_roethlisberger]

23 hours ago, Joe said:

For what its worth as a mere mortal to the experts on this forum. 

I owned a 2001 Silver V11 Sport new that I later added a Fast by Ferracci drop in pistons, FBF Power Commander w a custom map made to make peak horsepower, lastly FBF carbon exhausts. What Mike Wells & I created was one of the coolest deep toned 2v Big Block Guzzi's ever.  We also created a vibration machine that even with Throttle Meister heavy bar end weights couldn't resolve, leaving you with numbness on demand.

Many years later, my new to me, low mileage V11 Sport Rosso Mandello is running a custom map (idle is higher), everything balanced to spec with stock bar ends, no power commander. Riding to the 22 Spine Raid last year, rarely did it create enough vibrations in the seat or the hand grips to create the same sensation as the FBF Silver V11 Sport, remember I'm 20 years older. 

*So there really is a sweet spot on these bikes as far as tuning is concerned to make them more comfortable, again devoid of the technical data supplied by the elite mechanics on the Forum.

 

I am sure you are correct that the "tune" makes a difference 

 

When I first bought my 2002 LM 21 years ago , I think I was a bit more interested in wringing out engine and suspension "performance" than I would be now, where today I would be focused on reliability, economy/efficiency, comfort, simplicity, and then only consider any additional performance opportunities that don't significantly degrade the first four  

 

After I get the baseline issues sorted on my bike to make it road-worthy again, "phase 2" will be to revisit the state-of-tune for this very reason to simplify and step back from "top HP" goals and instead focus on a smooth and efficient tune.

[al_roethlisberger]

On 1/13/2022 at 12:42 PM, Chris Wilson said:

Yep, got it!

Don't know why I didn't before.

Thanks, Chris.

 

I have a twin-plugged bike, and the ECU was reprogrammed by TLM to accommodate the ignition modification, which I don't recall was advanced or retarded after all these years.

 

Once I get Guzzidiag and the reader going, for reference I'll download the BIN so others can take a look at what was done.

[motoguzznix]

On 2/7/2023 at 12:39 PM, Pressureangle said:

Correct of course, but you've missed the point. It's not the engine we're concerned with, but the handlebars and footpegs and seat. 

Ok, I understand your point and I agree. 

My point was related to an engine that suffered of very severe engine vibrations that could not be cured by simple anti vibrational measures. Disassembling a motor is in most instances not an option when vibrations are evident. When assembling an engine with different pistons, rods and other tuning parts, the engine is usually out of the frame and the necessary parts to balance the engine are at hand. 

The advantage of an engine balanced correctly is that vibrations must not be killed because they are not generated. If balancing the engine with the correct counterweight the vibrations generated are reduced to a theoretical minimum. When the level of vibrations is low or zero, parts will not resonate because they will not get stimulated. 

And there is an other big issue cured by balancing: The vibrations created by the rotating and oscillating engine parts will be transmitted via the big end and main bearings, engine mounts into the frame, handlebars, footpegs and so on. So the bearings must handle additionnal forces when the engine ist not balanced correctly. This contributes to additionnal wear in the bearings and reduced service life. These forces get higher when rpm climbs. If high rpms are a goal, balancing is important.