gear selector box.

[Bevel bob]

My 250 NC 5 speed has a tendency to miss 2nd gear and find a neutral followed by the next gear change selecting third. It also is sometimes reluctant to change from 2nd to first while rolling to a stop. Any thoughts would be helpful. There is very little information on re-furbing the selector box , wear limits, spring lengths, shim fitting etc. I think Lacey supplies bushes .

[Jordan]

Sounds like the selector box is OK, because the next change goes to 3rd. That means the ratchet mechanism did its job to push the drum to the 2nd position.
The problem may instead be inside the gearbox. Ducati gear material is very ordinary and prone to rounding of the side dogs. It gets to a point that it will push them apart, rather than staying put. The dogs are undercut and actually should help pull the gears together into full engagement, but wear defeats this. And/or, there may be a bent/worn selector fork.
Sometimes gears can be reshimmed for improvement, but it's a laborious task and new parts would be nicer. Best way is to have new parts, then shim it to perfection - not just to production standard - for best performance and life.
Sometimes gear changing technique helps. Keep pressure on the lever until the clutch is fully engaged.

[Bevel bob]

Thanks Jordan, I had come to the same conclusion, reluctantly!, the selector box has some wear in the bushes and a little slack in the action . A slow and deliberate change holding the pressure on the lever until the power is on does work and points to wear on the gears being the problem. My fault ,should have spotted it,but was distracted by all the other issues with the motor.I also think I have shaft that is slightly bent that will need sorting.

[machten]

I wouldn't be too hasty. I think I've posted this before, but...The fact the return mechanism works doesn't mean that the selector box is working as it should. That may well be right, but there is a lot in a worn selector box that could result in the same symptoms. I've recently refurbished my 750 Sport selector box and when you add up slop between the lever itself, the pivot arm for the selector box fork, the fork itself and the brass bushes, it adds up to a lot of slack. I put in some new bushes from Nigel Lacey and replaced my fork selector spindle. The next bit is only relevent to rearsets - but I also resurfaced the contact surface on the pegs and bushed the levers to fit). That selector action is now brilliant, the best it has ever been since I've owned the bike. I'd be looking there first before I split an engine. It's a good and pretty cheap thing to do anyway for a single. (You do need to have access to some reamers for the bushes though)

See earlier thread here...

http://www.motoscrubs.com/forum/viewtopic.php?f=3&t=1578

Kev

[Bevel bob]

Hi Kev, Yes I saw your earlier post, a local guy will press and ream for me ,so I will be doing that first. I'm booked to take the bike over to the classic TT and MGP so I need to act soon.

[machten]

I'm booked to take the bike over to the classic TT and MGP so I need to act soon.

In the Australian vernacular..."You lucky bastard!"

Kev

[Jordan]

I wouldn't be too hasty. I think I've posted this before, but...The fact the return mechanism works doesn't mean that the selector box is working as it should.

Kev

It's definitely wise to check the easy things first, even if they aren't the prime suspects.

[Octane]

I had a similar issue on my Mach 1 a while back. I would find false neutrals when shifting from 1st to 2nd, and it would occasionally pop out of gear. I found the spring behidn the detent ball had broken, so the detent ball wasn't keeping the plated located properly once I released the shift lever.
I put in a slightly stiffer (than standard) spring and the shift is as crisp and accurate as anything I've ever ridden now.

[Bevel bob]

My spring is intact but its possible that its a bit tired, Is there a measurement for the spring.? If OE parts were availiable common sense would say,Just fit a new one, However not having much luck with new (pattern ) parts just now.

[Octane]

I'm not sure on the exact spring size. I found one in a random assortment of compression springs at work which was around the same size, but a bit stiffer.

Have you tried fine tuning the little adjustment cam for the selector box? Maybe it's slightly over-shooting the gear change and it's only evident in the 1st to 2nd change. Mark it''s position with a sharpie on the selector box, then try adjusting it by 5 or 10 degrees each way and see if the problems gets better or worse.