Gearbox problems - internal or selector box?

[bendik]

I had some problems with the gearshifting on my 250 racer and was wondering wether there is a way to determine wether the problems are in the gearbox itself or the selector box?
I am sure some of the problems are related to shifter positioning, but there seems to be something mechanical also

My problems were these;
Difficult to select 2nd from a higher gear
Often misshifts when going from 3rd to 4th, getting a false neutral. Will then hit 5th..
Often difficult getting from 5th to 4th at the end of the straight. Also difficult to then go to 3rd, would often need to not only let the clutch out but also get on the gas again before selecting 3rd

[Duccout]

Hi,

Have you tried selecting the gears with the bike on a paddock stand with a dead engine? While rocking the back wheel and selecting each gear in turn then releasing the gear lever, it should return to the centre position with an audible click and then be ready to select the next gear; if it has not clicked back into place, when you try to select the next gear nothing will happen, you will just select the current gear again. If you have to physically move the gear lever the last bit to get it to return and click back into the central position, then the eccentric needs adjusting.

The selector box is finicky and if components are worn it will not play ball. Often the 'coffin' that holds the spring will wear and allow the assembly to twist slightly; this and worn bushes or even wear on the splined shaft will prevent the selector from working properly. It is not a great system and is a messy job to assemble. Or you may have problems in the gearbox itself......

Cheers,

Colin

[bendik]

It felt ok on the workbench, but on the dyno I had the same problems getting into 4th. However they were worse on the track and then the extra issues also popped up.
Will double check the return, but that "feels" ok

[themoudie]

Aye bendik,

"Feeling OK on the workbench", is one thing, but have you gone through the steps described by Colin?

Any wear in the bushes, detent ball/plate, washers/shims/springs, or a maladjusted eccentric, will have you scrabbling around on circuit, either bouncing valves, or missing braking points and apexes, whilst trying to "find" those gears. DANGEROUS! Both for you and your fellow competitors!

Properly set up and adjusted, the selector box should be smooth, returning to the central position, with an audible "Click", before selecting the next gear. Tramping through the box, will get you nowhere fast, being a little slower and feeling the dogs engage through the gear lever before applying the power makes a difference. I don't race ....... but the same methodical assembly/checking/adjustment and operation applies on the road.

Alternatively, you could invest in one of Nigel Lacey's modified selector box mechanisms, available on his website.

Hope you get it sorted and good health, Bill