gearbox whining

hi
my 1971 st50 has a gearbox whining noise on acceleration in 1st and 2nd.any ideas any one

Whining in the lower gears usually means a problem with the lay shaft bearings or gears. In top gear the drive is direct through the main gear shaft with the lay shaft running in unison but carrying no load. Drain the oil and clean the oil filters to check for any small metallic particles which would indicate a bearing or gear breaking up. If you can't see anything and everything runs okay apart from the whine, you could leave it alone meantime.
Many gearboxes run for years making a whine, only if the noise changes to a more mechanical grinding noise or if a roughness becomes apparent would it be worthwhile doing a strip down, unless you want a rummage around inside anyway.

hi iain
thanks for reply rebuilt bike 3 or 4 years ago 10500 on clock but not the engine just fitted new oil filter , clutch plates ,oil seals + clean oil and a good clean up.
have not used bike this summer very bad.can not remember if whining before