A10 gearbox problem

[Robinson]

Hi I've recently fitted a refurbished gearbox to my 1960 swinging arm model A10. The gearbox worked fine to start with but 600 miles later I'm having issues.
1. With the bike on its stand, in neutral and with the engine running, the back wheels spins. I can stop it with my foot, but why does it spin, its not as though the clutch has any effect when its in neutral, its as though internal components are dragging?
2. Gear changes into or out of 2nd and 3rd gears are getting very clunky, no matter how I try and match the revs, blip the throttle etc
Anybody got any thoughts, or are all A10 gearboxes clunky in 2nd and 3rd gears?
Cheers, Cliff

PS.I'm using Castrol GP50 oil in the gearbox

[JulianS]

Question 1 - they all do that.

Question 2 - no they are not all clunky, before dismantling the gearbox check the primary and rear chain adjustment and check the clutch is lfting square and not dragging.

[idie]

The rear wheel will always spin due to the oil drag in the box. Clutch drag will cause problems. Has play developed in the box allowing the mainshaft to move so losing some of the clutch push rod movement. Has your clutch lever got a 1 1/8 spacing between nipple and pivot to get max movement on clutch mechanism.

[Robinson]

Hi, Thanks to you guys who have replied to my queries so far.

Reply to idie: not sure about increased end float play in the main shaft, I will have to remove primary chaincase cover and dismantle clutch to check that. Yes there is 11/8" between the centre of the cable nipple and the clutch lever pivot point.

Reply to JulianS: The clutch is lifting square,  I adjusted it carefully to ensure there is no swash on the pressure plate. The primary chain is a bit on the tight side, what effect do loose/tight chains have on changing gear?
I saw your reply to another post regarding A65 gearboxes where you attached to service sheets. Do the problems highlighted in those sheets apply equally to an A10 gearbox?

Cheers, Cliff

[JulianS]

Tight chains can cause a harsh gearchange.

The A65 and A10 boxes are quite different. The A10 swinging box is a good unit, largely unchanged since it was introduced in late 1953. The A65 box had a number of changes, due to problems including  pinions, quadrant etc.

If you think the box is the problem rather than the clutch and/or chains dismantling and checking is the only way forward,  but I would check those first - if you have the 6 spring clutch they do have a poor reputation.

[idie]

A tight primary chain can cause the gearbox to whine as it is putting a severe loading on the bearings. So can cause problems with gear changing. Certainly affected  my BSAs.

[Robinson]

Hi again,
You've both convinced me, I think the primary chain is too tight, its a lot tighter than I originally set it, so not sure if it moved when I re-adjusted the rear chain which had gone slack. Certainly a good place to start as I don't want to have to strip the lot down again any time soon.
I'll let you know how I get on.
Thanks, Cliff

Ps. Its a 4 spring clutch

[idie]

When you readjust the chain make sure that the adjuster is pushing the gearbox forward, this stops the rear chain from snatching the gear box back. If you have to tighten the primary chain at any time make sure you wind the adjuster forward again to take up all the slack.

[Robinson]

Hi Julian S and idie.
I re-tensioned both chains on Tuesday as you suggested, and ensured both the pivot and adjuster bolts were tight, and that the adjuster was wound forward to eliminate backlash and prevent the clutch sprocket being pulled back by the rear chain and tightening the primary chain up again. I had also had a problem with the clutch cable going slack which revealed itself when the nipple on the handlebar lever pulled out, ( fortunately in the garage). Anyway, fitted a new clutch cable and went on a 200 mile tour of the Yorkshire dales with some friends yesterday, and the gear change was very much improved and when I checked this morning the primary chain tension is still correct. So problem solved and thanks very much to you both.
Cheers, Cliff