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
Welcome Greg. You seem like a great friend to have. I’m not qualified to answer, except to wonder if the flywheel/alternator nut could have come loose and caused this??
Thanks for both replies--I can say that, the crank seems very tight with no play, and the 30mm nut holding the flywheel is very secure. Could repeatedly pressing the starter button and attempting to start the bike while rolling with dead engine cause this?
If the torx bolts were all sheared in roughly the same place on the shank, something must have seized the flywheel solid while the crank was turning. I would have expected that the engine would have catastrophically stopped with a bang/noise. Intriguing indeed. Sorry I cannot offer any real advice. Good luck with the investigation and repair.
I suspect the starter sprag clutch malfunctioned and seized the starter gear in the wrong direction, and caused this. Engine seems fine, thank God!
It would take some significant torque to shear all those bolts...I would expect damage elsewhere. Crank splines? Starter gear?
The main cause of bolts shearing is, wrong grade of bolt. Overtightened, misalignment which in this case is unlikely. Has the engine had any work carried out recently? If the main bearings had failed sufficiently to cause the rotor to rub, I think the stator would have been damaged first, causing a failure in the electrical system.
The screws are mainly there to hold the assembly together. The dowel/s are fitted to give strength in the radial plane. A rotating crankshaft has a pulsing force, sine wave, acting through the flywheel and the components on it. It's this pulsing that puts strain onto any screws, that's why dowels are used. As a trick that was used in racing/tuned engines, was to double dowel the flywheel. I have seen aftermarket flywheels that haven't had the dowel hole drilled and therefore the assembly hasn't had the dowel fitted. There could be many reasons to what has happened but without all the evidence, we are pissing in the wind.
I agree with this one most likely using the wrong torque setting. The bolts should be threadlocked and only get 13Nm, max 15NM torque (not 15 ft lbs) when doing them up which is not that much, if they have all sheared with no other damage that is much more likely and it would probably have occurred during a heat cycle on the engine. Was the Belleville washer on the right way round for the center nut?
Noticed today while in my garage that according to the workshop manual extracts lying on my bench: 1098R does not have a dowel pin fixing sprag to flywheel 749R does have a dowel pin fixing sprag to flywheel
