Cannondaleriders

With greater revs comes vastly increased torsional vibration.
For example, a last-revison E30 DTM BMW (2.5 litre 4 cyl 355-365bhp) will rev to 9000 on long-distance endurance events without any issues at all but rev to 9500 and they are only good for 'sprint' races. Rev them to 10,000 and the flywheels come loose in no time, guaranteed.

No doubt but UPS doesnt rev his motor near what Class does yet they both spin them.I on other hand have run many motors over 12,000rpm and use it but have never spun a flywheel.We are missing something.

other thing is, the bikes. haven't heard much about them spinning flywheels?

OK, maybe I just have to much time to think?
One of my jobs at work is rebuilding hydraulic rock drills. This year someone figured if I had the patients for this, rebuilding hydraulic vibrators for our would be a snap. (going from memory, because all my notes are at work and I am currently laid off). After a little research I found that one check for a bad vibrator was to use a vibetach to check RPM. I spent almost $500 for one that would go high enough RPM reading (I think they sell something cheaper but, not as durable for field use). As I read the manual it explained how harmonic vibration affected the tach. a normal reading would raise a few needles/bars (I don't know what they are called) when the harmonics would come into play a lot more needles will raise and not nessaryly with only one peak. The window would be like a graph and it may be possible to compare the flywheel spinning engines with the others.

AS with my previous post here, the need for a counter balance is more important on a quad than a bike? We are balancing cranks but what about the counterbalance? Is it possible some of the gears are not timed the same?

Its possible and the cracks in case do head right toward the counterbalancer if that means anything.Do you own that tester?I have the cheap one for duing sound tests.Could compare tach readings using a D&M and Vibratach using the D&M for the baseline on both motors.Vibratach should then also be the same on both motors if not is different Harmonics I think.Originally when we were dealing with cams one of my goals was to do durability testing on a spintron which would also be capable of finding these Harmonic issues.Think of the $ automakers put into this area.You see weird little weights even on exhaust and tranny to get rid of these things.They wouldnt take the time or $ to do that for no reason.

Just to throw more fuel in the fire....

I have cracked 4 engine cases: 2 cable cases, and 2 hydro cases. All of them have cracked radially from the crank bearing. I have NEVER spun a flywheel. I ride sand, MX, and XC races. I love drag racing my buddies in the sand as well. I use all the RPM's that are available, use the clutch to shift, and don't fan it like a 2 stroke.

I think that the engine cradle and/or frame may play a significant role in cracked cases as well.

I think we are in over our heads on this one.Possibly only thing we CAN do is make flywheel stronger.

Other than maybe some counterbalance timing checks. anyone degree a counter balance shaft? maybe even start weighing the counter balance shafts

Steve; I spent the company'y money on that so I don't have access to it. actually I gave it to the operator who sets the pavers up and put them on line, thats why I went for the more durable one, so he can carry it in his truck. for some reason I'm thinking they had one for about $80. but it was a pocket sized unit and I don't know if it would have as good of a display.