Friday, 21 February 2014

Clutch

Having got the brake shoes back, I want to finish off a couple of cables that are cluttering up the workshop, before starting on the cylinder head. One of those is the clutch cable, and I would like to do a dry run of the clutch build. It's a dry run, beacause I want to spin the engine on the power drill using the crankshaft shock absorber nut, and I don't have the oil pump or any of the timing gear ready yet - because the head is not fitted.

So today I will fit the clutch temporarily, to have a look. First up is the basket, fitted over the cage & needle rollers. It's retained with new bolts and lock washer I bought from John Budgen.

Next up is the stack of plates and the clutch centre, preceeded by the final thrust washer. First problem appears - the new clutch centre nut is not happy on the gearbox mainshaft thread - though the old one still fits. This is the whole point of a dry build!

Push rod fitted!

The pressure plate comes next, followed by the cups, springs and the nuts. And the first outing for the clutch spring screwdriver I made a couple of years ago. Works fine!


The clutch operates very nicely using the arm on the other end of the gearbox, and the pushrod adjuster is screwed almost right in. Odd I think, the plates are in good shape but not wholly unworn. Most of them came from John Mitchell of the AOMCC. Maybe the pushrod is too short or there is a ball missing? The ball is certainly present in the adjuster cup...

Thursday, 13 February 2014

Brakes

Since I'm working on small fill-in jobs at the moment, due to a lack of spare time, I have been tidying up the control cables and making new ones. Before I fit the chain and chainguards, I need to sort out the rear brake as well. So it makes sense for me to visit the guys at Charles Johnson Bus & Truck Parts to get the brakes re-lined with a suitable modern material. This will enable me to finish & fit the front brake cable, finish the rear brake rod, fit the chain and top chain guard and sort out the bracket on the lower chain guard (which comes off a single I think - not a Square Four at any rate).

Brake shoe linings are made from soft and tough heat resistant materials mixed with compounds such as iron, brass, ceramic, and graphite. The lining can be either riveted or glued to the shoe. The lining has to create the maximum friction force from the meagre load you provide to the shoe using your hand on the lever, or the much greater load you can create using a modern hydraulic system. These materials have replaced the asbestos linings that were used with great effect until the ‘80’s, but which were shown to cause pleural and peritoneal mesothelioma, forms of cancer in people handling braking components regularly.

It’s almost inevitable that an old bike has asbestos brake linings. This is a hazard – particularly in the powdered form you meet inside an old brake drum. NEVER breathe brake dust. Assume that every brake system you are working with is hazardous and dispose of any brake dust properly.

Of course, like anything else in life, not all brake linings are created equal. A lining may be relatively soft, which will be quick to bed in and which would give medium to high friction forces relative to the load applied to the shoe. They would be suitable for normal road use, but would wear out quickly.

Or, you could specify a tougher material for heavier duty road use and touring which might also be suitable for some competition applications. This might last longer, but would need more force from the lever or hydraulics.

These days, most brake lining material is glued to the brake shoe using an adhesive designed to operate in the aggressive temperature to which the lining is subject. The lining is useful until the brake has run out of adjustment or has become ineffective.

Linings can be riveted to the shoe if required, and this is the traditional way. The disadvantage of riveted linings is that the rivet heads nestle part-way through the lining, meaning that the lining which is available for braking is much less thick and will require replacement sooner than a bonded lining.

So there we go. In a week or so, Amelia will have a new set of soft modern shoes. A few years ago, I was proud to be told by Danny (my MOT tester) that the brakes fitted to my 60 year old Bantam were better than those fitted most of the modern scooters he had in his shop.




















So a week later I have my new shoes, with Ferodo 3921 lining material bonded to the original shoes. They are a much better fit in the drum, and although I have only tried them by hand, feel much more 'sticky'.