In the early ‘90’s Ducati used two jam nuts to secure the flywheel, but replaced this design with a single very-fine-thread flange nut that carried with it an extremely high torque requirement.
For the 1999 models, Ducati redesigned the electrical system, going from a 350 watt design to a 500 watt three-phase system. This resulted in a new flywheel retaining nut design that unfornunately also had an oversized thread depth that would loosen-up, even when properly torqued and Loctited.
Ducati issued a service bulletin concerning the stock nut. If the nut spins-on with little resistance it’s out of spec and must be replaced with an upgraded nut from Ducati. An different rotor was introduced for the 2001 model year that put an end to the issue.
Prior to 1999, the factory-installed nut did not commonly loosen, but they present a more serious problem if not properly torqued during (say) an aftermarket flywheel replacement. When they come loose, they’ll often damage the crankshaft splines. On pre-1999 models, you just need to replace/retighten the nut to the correct torque.
Except for these two model years, you’ll not get a loosening problem unless you’ve removed the nut for some reason. When you go to reinstall it you’ll find that without the proper tools it’s VERY difficult to immobilize the crank (which is necessary to reach the high torque) and many shops/owners don’t understand how critical this is. The use of this kind of nut in this particular application is on the envelope of fastener design.
Symptoms
The first indication of a problem is a knocking noise from the left side of the engine that doesn’t go away when you pull-in the clutch lever. (The knocking noise sounds similar to the clutch knock at idle.) Excessive clutch tang wear and a broken clutch pushrod at the o-rings are also an indication. If you look into the timing inspection window on the left cover you can see if the flywheel is wobbling. Another apparent symptom is sluggish initial turnover when starting the engine because of interference caused by loose parts.
Solution
The solution is to replace the castellated nut and retorque. If the nut spins-on with little resistance it’s out of spec and must be replaced. Alternatively, Nichols Manufacturing offers a replacement double-nut (similar to what Ducati used in the early ‘90’s) that is self-locking.
www.nicholsmfg.com
Procedure
See Procedure here:
http://www.mad-ducati.com/Technical/...torCover2.html
Place a piece of soft metal (like a copper coin) between the starter pinion and the first idler gear to immobilize the shaft while you tighten the flywheel nut.
The best way is to make a tool to hold the rotor.
On engines with a solid countershaft drive gear (the gear behind the flywheel assy,) Ducati now recommends torquing the nut to 270Nm. On SP/SPS and other models where the countershaft drive gear is grooved where it sits on the crankshaft, you can only torque to 190Nm, to avoid damaging the gear.
The bottom line is that if you don’t have a 1999 or 2000 model year bike ... and you haven’t touched the flywheel nut ... don’t worry about it coming loose.
Linear Mode
