Hi people, The rev counter on my recently acquired 1995 carbie 900ss works intermittently. It either indicates rpm (seemingly) accurately, or not at all. I just wondered if this is a known symptom and, if so, what the cause of this is? Otherwise, what should I check first (I'd have guessed that a faulty cable would prevent the rev counter working at all) and subsequently? If anyone can help with this, I'd be grateful!
Have a look at the inner ends of the cable and where it fits either end. They are square and can round off. This may be causing the intermittent symtoms you have.
Do as Desmoquattro says............and if the ends look OK, make sure the brass ferrule is up at the speedo end.........also clean the cable inside.......loads of WD40 or white spirit should clear any crap out, then wipe down the inner with WD40 on a rag; then re-grease and re-assemble......don't over grease it. However, while it is off at the engine end, start the bike and watch if the drive pinion rotates OK, especially when you blip the revs up.......you could be very brave and stick on a thick leather glove and try to hold the pinion with your fingers while it is ticking over.......if you can stop it or it is intermittent, it may be sign of another more serious problem.
I had the same issue. The ferrule on the end of the cable at the cylinder head drive tends to corrode. Lots of dissimilar metals and Ducati corrosion going on. I had to clean the aluminium corrosion from the threads on the drive in the head with a brass brush then put on a new cable.
Thanks very much to Desmoquattro, Arquebus and corrosio non forsit for the helpful and tactful advice. I will do as suggested, and trust that the intermittent functioning is not the sign of the more serious problem Arquebus mentions!
What can also happen is the drive worm gear inside the head can get worn. Try the squaring off first though, common prob happened to me and lost all reading.
That is what I am hinting at..........the worm gear on mine was all chewed up because the silly nut on the cam pulley hadn't been tightened up enough..........some (and that's only some) 900ss had a woodruff key to stop the worm gear turning on the camshaft, but the majority of 750s and 600s didn't. Once the worm gear starts to slip on the camshaft, it can eventually get chewed and the pinion gear get's buggered up as well..... If it is a problem in that area, the OP may be lucky just by making sure the silly nut is really tight. Unfortunately if the worm gear is seriously worn or chewed up, there is a chance there will be evidence of it on the magnetic sump plug and the screen filter; and the particles will have got into the pulley and middle cam bearing; however most of it usually ends up at the bottom of the exhaust valve rocker cover. Replacing the worm gear (and those two bearings) can be done without removing the engine or the head, it just takes a bit of time and thought.
Nothing to add to the excellent answers above; I had that for a couple of years and seem to remember that Geoff Baines sorted it by replacing the cable (with a good used one). If it helps to know, it's not an MOT failure.
Thanks to Arquebus and Cobbett for the very useful further clarifications. How would I manage without the forum?
Hopefully it will be a simple solution and not the worst case I described............however, you will need some tools to help you with the silly nut if it needs tightening or if it is the worst case........ You can make a silly nut socket from a spare socket or you can buy one, but you still need to hold the pulley still...........I used a large open end spanner that fitted tight around the socket and drilled two holes in it for two M6 bolts which screw into two of the pulley holes.
