[greg328]

Hello--need some insight into what may have caused the following--my friend's 2007 1098 suffered a charging failure--after diagnosing the issue--I surmised a bad stator--as battery and upgraded Mosfet VR are new---stator is original and 13 years old.

We removed the left-side engine cover, to reveal that the stator was chewed up, 8 partial T25 Torx bolts rested inside the stator, and the circular barrel magnet was magnetically attached to the stator, not to the flywheel as originally attached/intended. At first glance I thought maybe the 8 bolts simply worked themselves out, but no, they were all sheared off and about half length. I've yet to remove the 30mm flywheel bolt to access the assembly, but soon will.

What sort of force could have caused this? Something tremendous must have occurred to provide enough force to twist off the magnet from the flywheel. Of course, the magnet is normally secured to the flywheel via the (8) T25 Torx bolts, inserted through to thread into the circular starter sprag boss. Could the sprag clutch have seized, thereby preventing rotation (in the free direction) and caused this?

Smart minds please chime in! I will repair for him, but would like some insight and opinions on what may have caused this situation!

Greg
Austin TX USA

 

[Buhgaboo]

While I haven't encountered said problem my gut says the bearing on the shaft is bad...given the rpm that assembly spins at any imbalance could overload the shear strength of the screws and the rest would go like dominoes...before you bolt a new one on...I would look for any runout/play on the shaft and the bearings

 

[greg328]

OK thank you--I'll look at that as a possibility. Owner has told me after first failure, (bike died while running--and would not start--due to bad stator not charging system)--he towed it home. Next day after time on battery tender, he started it and rode over to shop. From there bike would not start again--dead battery. He says engine runs fine when running. Can a bad crankshaft blearing be felt when running? Can bike even run with bad crankshaft bearing? I wonder how he got it started again, in the current condition?

 

[Buhgaboo]

OK thank you--I'll look at that as a possibility. Owner has told me after first failure, (bike died while running--and would not start--due to bad stator not charging system)--he towed it home. Next day after time on battery tender, he started it and rode over to shop. From there bike would not start again--dead battery. He says engine runs fine when running. Can a bad crankshaft blearing be felt when running? Can bike even run with bad crankshaft bearing? I wonder how he got it started again, in the current condition?

From an engineering angle...the bolts sheered off...from either an imbalance or from jerk...that shaft out of balance would register more of a high frequency harmonic that suddenly went away rather than a persistent clunk you'd feel with say the crankshaft...it wouldn'tt take much to be catastrophic at the rpm the shaft spins at...I suppose some more question should be asked...any work done to the flywheel...bike ever been in an accident...any visible cracks in the case where the bearings are...any history of oil leaks...the answer is there somewhere

 

[greg328]

Thank you Buhgaboo--I'll keep the thread posted with what I find---still puzzled though---I can't imagine how a mildly shaking crankshaft could cause such force as to shear the circular barrel magnet off the flywheel. I feel like something would have seized the magnet tightly--but---what would hold the magnet in place with enough grip to separate it from the flywheel? Surely the magnetic force between it and the stator is not enough "grip"..!?

 

[Buhgaboo]

Thank you Buhgaboo--I'll keep the thread posted with what I find---still puzzled though---I can't imagine how a mildly shaking crankshaft could cause such force as to shear the circular barrel magnet off the flywheel. I feel like something would have seized the magnet tightly--but---what would hold the magnet in place with enough grip to separate it from the flywheel? Surely the magnetic force between it and the stator is not enough "grip"..!?

A high cyclic fatigue in a bolt would be sudden... but it is the accumulation of many many stresses....those add up pretty quick In a motor that revs to 10k rpm

And unless he parked next to an MRI you could rule out a magnetic force...but if the barrel was out of balance in some way...over time the result would be the same...

 

[belter]

i've never seen the little screws come loose, or come out without some resistance. even with loose or wound off crank nuts. bizarre. sounds like they're broken off at the start of the threads in the starter clutch drive hub, maybe it's loose in the flywheel. pretty odd for there to be enough torque from the starter to break them though - 8 of 6mm screws can take a fair load, even in shear. maybe if they were loose?

 

[xracer]

i've never seen the little screws come loose, or come out without some resistance. even with loose or wound off crank nuts. bizarre. sounds like they're broken off at the start of the threads in the starter clutch drive hub, maybe it's loose in the flywheel. pretty odd for there to be enough torque from the starter to break them though - 8 of 6mm screws can take a fair load, even in shear. maybe if they were loose?

The rotor is doweled so I can’t see how the bolts sheared unless the dowel wasn’t in AND the bolts were lose. Never seen the problem with Ducati but have done a few Aprilia’s which when the bolts come out take the stator with out in a big way.
And I never reuse the shitty torques heads. Most useless head ever devised.

 

[duc96cr]

I’d bet the bolts were either loose and sheared, or overtighteNed and failed. Have they ever been loosened before ? You might be able to tell if the bolts were tight by measuring how much broke off. Not everyone uses a torque wrench.

 

[belter]

forgot about the dowel. although the starter drive ring piece isn't doweled. that's just weird. maybe torque till stripped is higher than torque till broken, hence breaky.

who knows, fix it, move on.