Motoscrubs.com

Daft question - what's the shift pattern on a 4-speed? I thought I'd check I can select all gears before I build up the rest of the motor. I expect it to be 1 up, 3 down with neutral between 1st and 2nd. If so, I can't seem to get 1st on the bench and there seem to be some extra neutrals.

Ian

All 4speed singles have this shift pattern (here the 160 Monza jr.)

cheers hans

Its possible to have the box shaft connected 180 degrees out to the selectors.You will have to rotate the rear wheel while selecting gears.

At what stage of assembly are you? Cases assembled or apart? Clutch assembled? Is the selector box installed or are you selecting gears by turning the shift drum shaft? Ideally for testing, you would be turning the input shaft by hand while effecting some drag on the output shaft. As you turn the shift drum, the engagement dogs on the gears can then align as the drive gears rotate and the driven gears stay, for the most part, stationary.

Matt

Thanks Hans, that's what I thought from looking at the internals.

Hi Matt. Cases are together with all new bearings and the original shims that came out. I took a load of photos as I took it apart and I believe I have everything back as it was. As part of the crankshaft shimming I did fit the input and output shafts, plus the shift drum.They all turned freely. Also fitted everything into the right-hand case and checked that selector forks moved properly before putting the cases together. I'll have another fiddle around tomorrow night to see if I can get it into first gear, but it's so stiff to turn in the other gears so I think it'll have to come apart again.

Ian

I have no experience with 4 speed Ducatis, but assuming they are similar to 5 speed:

To ascertain correct selector operation, you can take it off the bike and mount it in a bench vice - careful not to crush it.
Then, you can see the output shaft that connects to the cam drum in the bike's gearbox.
It should rotate to the next selected indexed position as the foot change lever is moved, both ways.
You might be able to improve accurate selection with the adjustment eccentric screw, near the pedal shaft.

If all is good with the selector, you could check the operation of parts within the bike's gearbox, by turning the cam drum while moving the gearbox shafts, as mentioned - with the selector box not installed.

The selector box seems OK, but I will check again tonight. Perhaps the pedal return spring is a little weak, but it clicks the forked output shaft round smartly when the pedal is moved.
Ian

But does the pedal snap back properly, ready to select the next gear?

OK, things are looking better. I had another look at the selector box and sketched the angle of the output fork in each position. I hadn't realised that it can turn right round, but the pedal only moves it when it's "in range". I don't think this was causing any issue but I was able to check that the selector and gearbox were in matching positions. Can now get all 4 gears, although 1st needs 2 people, one to hold the output still, and the other to rotate the input and operate the pedal. Should be much easier when the engine is running and there is a chain.
The pedal returns nicely for downshifts, but needs a little prod to get back to centre on upshifts. I think this will be OK when riding.
So now my doubt is about how stiff it is to rotate when in gear. I think it gets stiffer in higher gears, but only once the backlash is taken up. Is there a drag torque figure I can check against?
Ian

Ian,

you will experience that shifting will be easy when the engine runs and all gears/selectors are immered in oil. Don't worry.
A difference in up- and down-shifting might be regulated with the excentric adjuster screw/locking nut mechanism in the gear selctor box. Try it out.

cheers Hans