1974 450 MKIII 4th & 5th gear selection problem!

[themoudie]

UPDATE
Stripped out the selector box, gave everything a thorough clean with brake cleaner and checked for wear. Nothing appeared excessively worn, but the selector fork pivot pin was tight in the head of the selector pedal shaft? Had another pivot pin, which is a tight but smooth sliding fit and re-assembled the whole mechanism, with molybdenum grease.

Went for a wee run yesterday and made a few minor adjustments to the "angle of lever dangle" and acheived either faultless downward changes or upward changes through the gears, but not both! So, a small order for springs and shims has been placed and I'll have another go at the fettling once they arrive.

In the meantime, if this monsoon period eases I'll be out for a canter and not making any hurried manouvres or gearchanges.

Good health, Bill

[themoudie]

UPDATE

Spares arivved "toot sweet" from Nigel, so stripped the selector box out, again. Did some measuring so as to compare dimensions of new parts, with worn and see if there were differences. Used "very near" calipers, so not super accurate.

Detent ball, according to Clymer manual should be 11/32" (8.731mm) OD, mine, with no wear, measures 8.3mm and that is near enough a 21/64" (8.334mm) ball. So, either I have a selector box in which the factory fitted a non-standard ball, or the "small ball" conversion! Clarification, if you know, please! Re-used the 8.3mm ball.

Selector fork pressure spring (thin one) used 12.4mm, new 13.0mm, along with two new shims, as the old ones were rubbed.

I couldn't measure any dimensional difference in the selector fork springs, but the new one was more difficult to compress, so suspect my old one was suffering from fatigue! OK! Age waits for no one! Held the "coffin" in the vice and wired the spring in place before tensioning and that made the whole assemby process much easier, rather than juggling, with pliers/'Mole' grips to hold the spring in place, whilst assembling onto the selector fork shaft.

There was, after close inspection of the exploded/cut away diagrams in the Clymer manual, a shim missing from the shaft of the selector pin drum. So two new shims were installed.

Re-assembled, with molybdenum grease, installed the cover, with the new countersunk, allen screws, much better than the old straight cut screw heads, torqued to 9Nm (6.638ft/lbs). All the selector positions could be selected, without delay or having to nudge the lever to releave the detent ball. Re-assembled the box back onto the engine and torqued the screws, to the same torque as the box cover.

Will take the bike for a canter and see how things go.

Good health, Bill

[themoudie]

FINAL UPDATE

A good 45 mile canter this afternoon in the gathering gloom of a dry winter's day and another "monsoon" forecast, saw the selector box perform better than before. All gears now select, both up and down the box, apart from an occasional reluctance to drop from 2nd to 1st, which will require some minor adjustment of the cam controlling the selector spring coffin/pedal angle.

The road conditions were atrocious, with water, macerated leaves and conifer needles, either spread thinly or in rows up to 6" deep up the middle of the carriageway, mud from the verges as a result of tractors bouncing off of them and that ubiquitous strip of rubber dust/oil/diesel and soil that forms up the centre of the carriageway at this time of year. Go canny and keep riding the "old birds"! Maybe the monsoon will wash the roads clean?

Good health, Bill

[Dan C]

Just came in on this thread. For those that are interested Sports Motorcycles (now located in NZ) make a replacement selector box.
Its too expensive for me, I can only afford Bill's approach of carefully rebuilding the original with unworn components, but its probably a good solution for those that can afford it.

https://sportsvalve.com/gear-selector-box/

Cheers Dan

[Duccout]

Hi Dan,

Yes I've seen those and they look good, especially if you have deep pockets! Does anyone know why the Singles one is $860 and the twins $1010? AFAIK the selector boxes are the same?


Colin

[George]

Nigel Lacey sells improved selector box for about £340

[themoudie]

Aye George,

I was about to post the same. To my untutored eye Nigel's offering appears to be a better engineered solution and made by NOVA in the UK, no "offshore" outsourcing and quality, skills retained in Blighty!

I was out through the "Lakelands" of eastern Perthshire and Angus on Sunday for a cool, but sunny and very wet road conditions run of over a 100 miles and the rebuilt selector box was 98% fine, just an annoying occasional 2nd to 1st downward change in traffic that needed a wee touch to reseat the fork before selecting 1st. Many roads were like river bed trials sections and all the roads across the Isla river between Meikleour and Kirriemuir were impassable to all traffic.

On two occasions, in Perth traffic light queues, the 'Old Bat' got fed up and decided to cough, so the traffic had to wait whilst I hopped off, folded up the footpeg and brake pedal, restarted, with a single swing, reversed the footpeg and brake pedal process, then with a "Thank you" moved off from the lights as they changed to green.

Cheap and Ducati have never been bedfellows and I'd much rather have a sorted single that I can use in all weathers than the latest "fly by wire, multi-program rocket" for high days, holidays and 'Green Willy' posing!

Good health, Bill