Qn: Is it OK to fit the new flanged alternator nut without a cup spring washer on a 900ss? Current replacement nut if fitted with the original spring cup washer might well foul the alternator casing beating/housing. Torquing it down and offering up the cover, there is no gap between the nut and the bearing housing face, it protudes into the recess by about 1mm. The OEM alternator nut fitted on my motor p/n 74810181A a thinner nut without flange; is N/A; It was fitted over a separate spring cup ('Belville') washer, p/n 40029040 n/A; A superceded p/n 74810131A for the alternator nut is now a flanged nut, with superceded p/n 79950012A offered for a Cup spring Washer: See here for parts diagram https://www.ghmparts.com/motorcycle-parts/ducati/900-ss/1992/crankshaft I suspect the superceded washer is the same thickness/profile as the original. The spring washer thickness I have is 3.75mm thick (uncompressed). Thoughts: I would tend to think a spring cup washer here is important, more important than loctite.- Interestingly, for a 1997 600ss no spring cup washer washer used, in https://www.ghmparts.com/motorcycle-parts/ducati/600-ss/1997/crankshaft
Further Qn: Perhaps the rotor profiles changed - i.e slightly thinned down for the later bikes, which would therefore present no problem?
OK, I think i know exactly why I have the problem: The engine was fitted with lightened steel flywheel donated from a 600ss. Most likely fitted with the 600ss rotor. (some) 600ss were fitted with only a flanged rotor nut, and no cup washer. That flywheel-rotor assembly is likely to be thicker as a whole and will not take a cupped washer. It had been fitted with an earlier (n/a) non-flanged nut and cupped washer by the modifier (luigi's). So, ideally, I need to find a 24x1mm 74810181A nut, which is now N/A from Ducati; OR Find a pair of jamb nuts - ony available from USA. Any help finding either of these two solutions above would be welcome; I haven't found one yet. OTHERWISE, I have to go with the new flanged nut w/o a cupped washer and rely on the loctite and proper torquing. Which I will do if I must. Ducati REF : 75010571A M24X1 is thinner non-flanged for crankshaft clutch side; That may do to team up with a cupped washer. Or use two together as jamb nuts.
Problem solved. Confirmation: Boss of 600ss alternator is thicker. Solution: Three choices. Two with cupped washer, one without. Recalled that Luigi Motors had fitted the 600ss flywheel for previous owner. Called their tech dept: Replied, Yes the donor flywheel is not just thicker rim, but also the boss stands further out, AND; Replied that they would have used earlier slimmer nut (N/A) and cupped washer, but that otherwise they also turn down the centre of the rotor to take new flanged nut and cupped washer. Replied, certainly, I could use the clutch crank nut plus cupped washer, its same thread. Replied certainly, its OK, as in the 600ss, to use the flanged nut with loctite on the 900ss, but without the cupped washer, so long as its torqued down nicely.
Yeah., have to solve it somehow, in the best way.. w/o too much of a rush. Really I wanted a clear answer within five minutes! Took three days for me to solve it since I posted this one. Most things involving builds and service are fairly straightforward really, but otherwise I like to record a tricky emergent issue which lacks an immediate answer, pertaining to the marque, here in forum as I go, in case it ever serves the community of ss riders; It might, especially as time goes on. This one Involved extra round of dismantiing/re-assembly making all the checks, and sleeping on it, in order to come to a firm decision. Stroke of luck that I recalled in a dream, last night my conversation with prev owner at point of sale a few years ago, and that he had mentioned Luigi's. And lucky they are still in business, after all this time - many years. Luigi's tech dept were quick to answer my call, understood me immediately, and straight to the point. Quick to hang up too, when I said thanks, goodbye! Call lasted 3' 30s only - worth approx £1.36, something like that. Could I have saved myself three days? Approaching the problem with care and thought, led me to the solution, and upon that, my eventual recall, which was useful for confirmation. I forget a lot of stuff these days, but I suppose it's all there really, I just need to access those useful clues like Sherlock Holmes taught me, .
