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...

Friday, 14 February 2014

Cables & Cable Making

This is the section where we deal with those cables that you oil regularly, that operate your clutch and your front brake. They are an important part of your biking experience, not only for your safety but also to make the experience a pleasant one – there something rather magical about you & your bike cruising smoothly along a sunny lane, with everything operating as it should. One of your main connections to your bike is through those control cables:

Cables & Uses

Since the dawn of the bicycling era we have had the Bowden flexible cable. Your typical old motorcycle will have several – for the front brake, the clutch, the throttle – and maybe for the back brake, an air slide, a decompressor and the magneto as well.

You may have noticed that these cables are not identical – in fact there is a whole variety of components used in control cables throughout the biking world. Like many other facets of life, cables have their own jargon. Here are the keywords:
You might recognise this as something like a Bantam clutch cable – though Bantams have the adjuster mid-way along the length of cable, not at one end.

Cables are manufactured from multiple strands of high-tensile steel wire, formed into a cable (i.e. twisted together in contra-rotating layers) provided with a compression resistant outer casing formed as a spiral of rectangular section wire, covered in a PVC or cloth sheath. The outer is finished with a pair of ferrules at each end, to protect the ends, and the inner is fitted with a pair of nipples, usually brass, to allow the handlebar lever or twist grip to pass the load into the cable, and the cable to transmit that force into the clutch, brake, or throttle slide.

Talking about loads, of course we realise that the load passed into a throttle slide is far less than the load that is required to bring a heavy bike to a stop with the front brake. So, we need several different cable sizes to cope with these loads – we don’t want to operate the tiny throttle of a BSA Bantam with a cable suitable for the rear brake of heavy bike like a BSA A10, because it would be way to stiff and the friction alone would probably stop the throttle closing.

So there are several cable sizes in use:
It’s useful to note, when you are buying cable components that several of those inner wire diameters are similar – 0.062” is not so very different from 0.075”, so be careful when measuring!

Outer Casings, Nipples, ferrules, inners etc.

So, to help you decide which components you need, here are some tables identifying the various parts:

Inner Cables & Ferrules

Here are the dimensions for the corresponding casings & ferrules for those cables listed above:

Nipples  

Buying Parts

There are a few suppliers offering cable making parts shown on another page. Shop around though, since nipple prices seem particularly variable. It is probably wise to buy your inner cable and outer casing from the same vendor.

Making up a cable

You’ll need to determine some details of the installation before you start on making up your cable. First of all, check out the cable size using the tables. Determine the length, during ‘Routing & Laying Out’. Look at the sizes of the appropriate ferrules – you must make sure that the ferrules fit inside the adjusters on the handlebar levers, brake plates or wherever or inside the levers themselves.

Then, take a look at your nipples – use the tables to determine what you might need, and then look at the handlebar levers, the brake arms or the clutch arm – whatever parts you are trying to control, to determine what nipples you need.

Note that some nipples will only fit certain sizes of inner cable, and that the handlebar levers you have may be damaged – bent levers result in poorly fitting nipples or ferrules.

Routing & Laying Out

Now it is research time. Try and get a look at some other machines, or pictures, to get an idea of how the cable was originally laid. Think about whether the cable routed behind the headlamp, in front of the yokes, down behind the fork leg or in front of the fork leg, which side of the fuel tank it went; under the engine, over the engine etc.

Keep it away from hot parts like the exhaust or cylinder head; make sure that there is enough length for the bends to be long and sweeping – with a large ‘bend radius’, and check that out with the steering in the straight ahead, full lock left and full lock right positions. Sweeping bends and good routing are the secret to smooth acting, long lasting cables.

Try and determine how the cable was tied to the frame and whether any guides or clips were originally used. Once you have this figured out, run a length of your chosen outer casing along the route and have a think about it. When you are happy, you can cut the outer casing.

Cut the Outer Casing

The outer casing is made from a rectangular section steel wire, hardened to provide a strong, flexible and incompressible outer casing. It’s covered with PVC to provide weather protection, retain lubricant and to make it look pretty (these are available in a variety of colours for all you Ariel Arrow sports riders).


All this makes them a little tricky to cut. Good side cutters or a sharp chisel are usable, but cannot provide a square end; not strictly necessary, but if you want it, and a square end allows the ferrule to fit over more of the casing and to be retained more reliably, you can use a cutting disc in a Dremel or similar tool

This results in a neat square end, and the PVC, which will have melted somewhat, can be cleaned up with a sharp knife.

Ferrules

The ferrules are often nickel plated brass or steel. They vary somewhat from supplier to supplier and may be brass and hard; or steel and soft. They should be a sliding fit over the end of the outer casing but if slightly tight their fitting can be aided with a little detergent or something more readily available (I usually use a bit of saliva! Good lubricant for rubber, saliva) they should not push the PVC out of shape when they are fitted.


If they are tight, you might choose to leave them as they are; you can tap them in one place with a dot punch; you can crimp them with pliers. After I had made a few cables, and never been very satisfied with any of these methods, I made a simple swaging tool from two pieces of ½” square bar. The bar has a variety of holes, sized to suit the OD of the ferrules, less 0.5 mm. Therefore I have a series of stepped holes – the ferrule OD, and the ferrule OD-0.5mm.

You will notice from the picture that this swaging tool, made from two bars, has the holes drilled such that they can be split. The modus operandi is to place the ferrule over the casing, and then place the ferrule in the tool such that the bottom 1/16” or so of the ferrule is gripped by the smaller of the two diameters in the hole.

The bars are then squeezed in the vice, and the ferrule is swaged such that it grips the cable outer casing. This works with all ferrule materials, but the harder brass ferrules are inclined to split when swaged. The steel ones work beautifully though.


First Nipple

Which nipple you fit first depends a bit on the installation. The trickiest part of making a cable is cutting the inner to the right length, at the second end. If you mess it up, the inner might be too short – in which case you have to start again; if you make it too long you just have to re-solder. So, I like to fit the most accessible cable last. Usually this will be the handlebar end, but in this example I am making a front brake cable, which is very accessible both ends.


Fit the first nipple over the cable end, with the belled-out side away from the inner case ferrule. It should be a nice sliding fit on the inner cable.

The next step is to prepare the inner cable for soldering. It goes without saying that these control cables are vital for your safety and proper preparation of the cable, proper soldering (including selection of the solder) is vitally important!

There are two types of soldering technique to consider – hard soldering and soft soldering. Hard soldering involves the use of a solder containing a high proportion of silver, and temperatures up to 750°C. This involves the use of a hot gas flame and incurs the risk of annealing the cable (since most hard solders melt at a temperature higher than the tempering temperature of the wire in the cable), leading to the possibility of the material yielding and the cable stretching. Soft soldering on the other hand involves the use of solder containing various proportions of tin and lead, and temperatures of below 400°C, which will not risk annealing the steel wire.

Soft solder is made in a variety of ‘recipes’ for various uses:
You will note that the solders listed vary in their strength according to the constituent components. A Lead free Tin/silver alloy is the strongest and therefore the most suitable for our purpose these solders melt at 250-300°C, suitable for a conventional soldering iron.

Solder is available in bars and wires, both with flux cores and without. I use non-cored wire solder, since I like to be able to control what flux I use.
So, you will need some flux. Metals at higher temperatures are even more prone to oxidisation than usual – so we need something to prevent oxidisation during soldering, otherwise the solder joint will be weak and will fail.


The impurities can be removed by mechanical cleaning or by chemical means, but the elevated temperatures required to melt the filler metal (the solder) encourages the work piece (and the solder) to re-oxidize. This effect is accelerated as the soldering temperatures increase and can completely prevent the solder from joining to the work piece. I like to use the liquid, Zinc Chloride based ‘Baker’s Fluid no.3’ for making cables, since it flows into the joint before any heat is applied and seems to be able to keep the join clean enough to ensure a successful joint every time.

Now, onto soldering the first nipple. Again, we use our swaging jig which has a number of holes drilled through it of such a size as to grip the inner cable, without crushing it. In the top of each of these holes is a small well of larger diameter, used to form a ball, or birds nest, on the end of the inner cable. We start with the inner cable in the swaging jig, with a length equivalent to about four diameters of the cable sticking out above the well, the jig is clamped in the vice, and the inner cable is not going anywhere.



Using a punch, we tap down on the end of the inner cable, in order to divide the strands:


Having divided the strands down into the well, we take a pair of long-nose pliers which, together with a small hammer, we use to bend the ends of the strands back toward the centre, forming a ball:

This is where the strength of the cable assembly comes from. The ball prevents the inner cable pulling through the nipple, and the separated strands provide a hugely increased surface area for the solder to grip the wire, such that the tensile load in the cable is pulling on a ball of solder and wire which cannot pull through the nipple.



So, now we can remove the swaging jig and see that the wire nest fits nicely inside the nipple. We are ready for soldering. Hold the inner cable in the vice, gently, such that the nipple is pointing downwards. We want the solder to flow into the nipple and to stay out of the inner cable; otherwise the inner cable will become stiff.


Lead rich solders are more reluctant to flow than tin rich solders. You may find it more effective to leave the ‘cup’ in the nipple upward using lead rich solder.



Dip the end of the cable, and the nipple in the flux, apply your soldering iron. It will take a while to heat the nipple up, but occasionally touch the wire with solder to see if it is hot enough. Remember that the work has to melt the solder – the soldering iron is used to heat the work, not the solder. If the solder will melt when it comes into contact with the nipple, then the nipple is hot enough. Proceed right away, since overheating will produce more oxidisation and will ruin the joint. Allow the solder to wick down the cable, filling up the birds nest in the nipple. Let it flow until it is about to drop out of the nipple, and you’re done. Leave it to cool.

Clean all the flux off with water. Flux is highly corrosive and you don’t want damage arising from yet more oxidisation. File any excess solder away, and don’t worry if you file off the ends of some strands that are poking out.


Second Nipple

Once we have soldered the first end, we can fit the cable back on the bike. Make sure that all the adjusters are in their shortest position, and wind them out two turns. We are going to make the cable as short as possible but in the event that we are a little over-enthusiastic and we make it too short, we want to be able to loosen the adjusters more if it proves necessary.

Make sure you fit the cable in its proper routing and that the second nipple is properly located in the brake lever, carburettor slide or whatever. Now, you will need to have the parts in their operating position to get the inner cable length right – throttle twist grip rolled shut, throttle slide down; brake handlebar lever fully ‘off’, brake plate arm moved such that the brakes are almost on, but not biting. You want the brake, clutch or throttle in a position where a small amount of cable movement will have it operating with the adjusters wound ‘in’ otherwise the cable will be over length.

Mark the inner cable with a small piece of masking tape in the location you want it cut – but don’t cut it yet. It’s helpful when cutting cables if they are ‘tinned’, that is, if the strands are bound together with ½” or so of solder. Fit the second nipple and keep it out of the way with a piece of masking tape. Dip the end in flux, apply your soldering iron and when it is hot enough, touch the cable with solder and allow the solder to wick up the strands. Now it won’t unravel when you try and cut it. Use a sharp pair of side cutters for this job.

Next, you can put the second end in the swaging jig and prepare the birds nest. Solder up the second end as before

Try it back on the bike, and use the adjusters to take up any spare length. If you have to unwind them considerably to get the brake, clutch, throttle or whatever workings correctly, consider releasing the send nipple and making the inner cable a little shorter.

Cable Management

Several methods of cable (and we are talking both control cables and electrical cables here) management were used in the 1950’s & ‘60’s, some more obvious than others, some more effective than others.

We are all familiar with the modern nylon cable tie, but whilst this is available in a wide variety of shapes, sizes & colours it is not in keeping with a 1950’s machine. That said, I have several on my Bantam and very effective they are.



You will find pictures of these black rubber ties in the BSA parts book for your Bantam. Originally made from Butyl rubber, they perish very quickly and fall off; modern versions are made from silicone rubber and will survive oil, petrol and sunshine very effectively

They can be used in a variety of ways giving the opportunity to strap cables of various diameters to handlebars, frame tubes or mudguard stays, and are used by passing the ‘T’ end through the hole in the opposite end, trapping the cable against the frame or passing the T through the middle hole, around the cable, and then again around the frame and into the end hole, holding the cable away from the frame. This looks rather neat I think.

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'.