250 monza won't shift

[flanker]

Ok I rebuilt my 250 monza: now the gear box seems stuck! The clutch is adjusted perfect. The gear selector box shifts great when out of the bike. The bevel gears are timed and the move appropriately. When I refit the cases everything moved. But the gears seem stuck (I think in second). Is there any trick to freeing them? When I pull in the clutch the bike moves well, just no shifting what so ever and I don't want to put tons of pressure on the shifting lever. I'm hoping not to have to split the cases again..... Oh yeah the kick starter works well too. Thx rob

[flanker]

Ok I put a wrench on the gear selector drum and was able to turn it to it perpendicular position (which I think is neutral as the back wheel spins freely. Still won't shift though. Thoughts?

[flanker]

Ok I found the cause... the gear box selector drum (male pin coming out of the right sided crank case) is really hard to turn. Did I tighten the cases too tight? Is there a remedy? thx again. Rob

[Jordan]

Just guessing, but if the selector cam-drum is tight because of negative end clearance, and the crankcases have been reassembled recently, it could be due to leaving out the centre crankcase paper gasket? Or maybe the gasket was replaced with a thinner one? Nothing wrong with that, but it affects the gearbox shimming. To restore factory spec end play to the various gearbox shafts, they need to be measured and re-shimmed. Got shims?
Working on the top end of a Ducati single is joyfully easy, but the bottom end is a different situation entirely, due mostly to the demands on gearbox shimming.

Jordan

[flanker]

Yep jordan I have shims galore! the gasket is in, I dunno maybe its thinner. But are you suggesting shim the gear box selector? wouldn't that make it tighter? Or do you mean the crank? Im having a hard time wrapping my head around why everything else works so well. I wonder if I should just lose the cases a bit and see what it does.... thx rob

[Nick]

Try hitting the ends of the transmission shafts with a wooden or plastic mallet (after first installing the nut on the end to protect the threads). Or use a piece of wood to soften the hammer blow. Often one of the bearings is not fully seated in the case, preventing the transmission from turning.

This was a frequent occurrence when I was building engines and a sharp rap with a mallet usually solved the problem.

[flanker]

yep Nick I tried that the transmission turns really well! its just the gear drum thats stuck, I even tried it around the drum and nada. my work pace is fast though and I almost have it apart!

[Jordan]

Yep jordan I have shims galore! the gasket is in, I dunno maybe its thinner. But are you suggesting shim the gear box selector? wouldn't that make it tighter?

There are shims at both ends of the selector cam drum as standard fitments. If the drum is tight, it could be that they are too thick and should be replaced with thinner shim/s.
Aim for nice easy turning with zero or very little side play, as too much play could lead to gear change operation problems.

Jordan

[Bevel bob]

I asked one of the top singles engine builders about the excess play on my % speed drum. He said that the 5 speed drum was not well designed and needed extra end float to allow the gears to select.

[Jordan]

I asked one of the top singles engine builders about the excess play on my % speed drum. He said that the 5 speed drum was not well designed and needed extra end float to allow the gears to select.

Not enough info. No problem with my 5 speeder, with minimal end play on the shift drum.
The cam pushes the selector forks in both directions, depending on gear. Too much end float means lost motion. The cam drum is only one thing that can be shimmed. It's possible to shim every gear, as well as the input & output shafts. If more than normal drum end play helped, it could be because there was an issue elsewhere, in which case more drum end play is a kludge. It can lead to premature wear of the dogs. Ducati gears are not made of very good stuff, and you really want to get everything as right as possible.

Jordan