Lost 4th Gear

[NealHooper]

This time last week i rode a 100 mile round trip my 500 VHA tele/rigid, all went well until 20 miles from home when a horrible rumbling noise appeared with the feeling of massive vibration, end float ? I was able to pull over quickly. I had done some 80 miles without any problem and not had any symptom in previous trouble free rides before.

After 10 mins to cool down, me and bike, and some consideration i investigated to find it kicked over, no noise,& started. I had a clutch and could engage a gear. So pulled off and to cut a long story short rode home 20 miles in 3rd gear, nothing untoward. But there was nothing where 4th should be - vanished -

It's a 56 GB box, had it and the clutch off in the garage. I removed face cover of the box revealed nothing, no nasty metal filings, then removed the case noticed the 4 retaining screws were hand tight, took the clutch off to withdraw the gears, nothing obvious was wrong, but the clutch basket was badly worn and the sprocket nut was not that tight.

So no apparent damage or wear, the gears look okay upon inspection. Awaiting a new basket before i reassemble but any ideas what went wrong, was it simply too lose or should i check anything else out more carefully.
Any ideas anybody. Neal

[paul.jameson]

Look at the gearbox end of the final drive gear on the mainshaft. You may find that the inner bush has worked its way out towards the kickstart end, thus preventing the sliding gear from engaging.

[will_curry]

4th gear is engaged by locking the sleeve gear - the one that goes through the bearing and
has the rear sprocket attached - to the mainshaft which is driven by the clutch. The locking is
done by sliding the gear next to the sleeve gear actually into the recess on the sleeve gear.
The sliding gear is splined to the mainshaft. Once engaged, the rear sprocket goes round
once for each turn of the clutch. Apart from Paul's observation there is the possibility is that
there is enough float in the gearchange mechanism to prevent the two gears coming together properly.

I would expect a VHA engine to have the short drive side mainshaft which would be too short
to align properly with the 56 GB mainshaft. These were extended to allow for the fitting of the
enclosure for the rear chain. This won't affect the loss of top gear but it may cause issues
with the primary chain and the engine shaft shock absorber