Advice on Dolls Head Gearbox just been rebuilt

Hi Ian

Re the dreaded norton clutch drag i would sugest checkiing the plates are flat

ihave a large surface plate and a sheet of emery cloth and give the steel plates a good rub this will show any high spots and get rid of any burrs ,the second gear issue may be adjustment of the rod between the two gear levers

Regards Roger

Hi Ian

Re the dreaded norton clutch drag i would sugest checkiing the plates are flat

ihave a large surface plate and a sheet of emery cloth and give the steel plates a good rub this will show any high spots and get rid of any burrs ,the second gear issue may be adjustment of the rod between the two gear levers

Regards Roger

Sorry i meant Steve not Ian

Roger

Sorry i meant Steve not Ian

Roger

You always need to finish primary chain adjustment by pushing it forward - ie start with it a bit tight then push forward with the adjuster. This takes up all the free play. Otherwise as you've discovered the bigger pull on the rear chain will pull the box backwards taking out the play in the wrong direction and making the primary too tight.

My rear chain runs very close to the inner primary cover at the back so have installed the split link with the spring towards the wheel rather than outwards just in case the extra width catches. A bit awkward to do it through the wheel spokes! I'm not sure how a felt washer would help?

At first, I disagreed, then remembered that the gearbox is pulled backwards by final drive tension, which is greater than primary due to gearbox multiplication of torque. So finish by pushing the gearbox forwards is correct.

In the years not running Brit bikes I had forgotten this. I must check if I have done it right on my own bike.....

I hear that modern bonded friction plates (especially the ones with Kevlar friction material) are more heat-resistant than the old-style ones with replaceable Ferodo inserts. But you can't do that to the chain wheel with inserts in them, as on the early clutches.

Paul

Another thing to check: is the gearbox properly clamped in the frame? The lower mounting hole on a Doll's Head box has a tendency to wear oval over time. If this has happened the bottom bolt will not effectively clamp the box between the lower frame rails, allowing the box to move even when you think the bolt has been correctly tightened. In turn this places stress on the upper mounting ears which can crack. The lower mounting hole can be bushed to restore the fit, ideally along with a new bolt. If doing this job check for gaps between frame rails and box and if necessary make a "top hat" bush for one side (or possibly both) to ensure a snug fit between rails and box so that an effective clamping action can be obtained.

Ian McD

I've done the same as Ian to give a bit of clearance 'tween chain and p/c case. Sounds not uncommon! Also re the primary chain tension, the view on this Forum seems to be to have it a bit slack (rather than a bit tight). From memory about 1" play but check that figure. My clutch is always better with a slack primary.

George

1" sounds a bit slack to me - mine is 3/4" (although always difficult to be precise). I agree too slack is better than too tight.