Monday 30 August 2021

The Final Build of the AJS V-Twin: Part 1

At this point, the bike was in a thousand pieces and scattered around various boxes in the workshop; it was time to apply whatever form of metal finishing was to be used on each part. First, an inventory was prepared for the bits and pieces to be outsourced for powder coating and plating – I always provide a list of the bits that are delivered as it’s much easier to check later that everything has been returned …or went missing!

Every bike that I have restored in recent years has been pre-1930 and for which nickel plating is appropriate. However, this bike is on the cusp of the nickel-to-chrome transition and I had decided that chrome plating would be more appropriate. Anyone that has read my previous blogs will be aware that I send the large items out to plating specialists (because they don’t fit in a 10l bucket of electrolyte) and plate all of the smaller components myself.

The petrol tank, exhaust pipes, handlebars and a couple of other bits were driven up to Castle ChromePlating in Dudley. I have used Castle Chrome in the past for nickel plating some of the parts on the Ariel V-Twin that I restored some years ago and the quality of the work was superb. At the time of writing this particular blog the parts are still with them ….so I’ll report progress in due course.

However, for the smaller parts that I intended to plate myself, I have only ever done nickel plating at home …so how to do chrome plating? It turns out that chrome plating in the home workshop in the same way that professional platers use is not an option because the chemicals used are pretty toxic. However, alternative processes have been developed that approximate chrome plating and are less dangerous for the amateur plater.

I chose to use Bright Zinc Plating which involves depositing zinc on the surface electrolytically followed by a passivation stage. Passivation is a chromate conversion process that involves dipping the zinc plated component into a liquid that converts the zinc into a mixture of zinc chromates, chromic oxides and zinc oxides and provides both a harder surface and, when polished, gives a reasonable resemblance to chrome plating. I had bought a Bright Zinc Plating kit from Frosts some years ago that I had not used up to now; I’m pretty sure that this is the equivalent kit that is now on sale and using what is referred to as the blue passivate.

But, first to experiment with the zinc plating process itself. I set up the plating bath in the same way that I have used for nickel plating and with an aquarium heater and air supply (to disperse bubbles that are formed on the surface of the item being plated) and put in a ~4’’ long section of copper tube. After a few hours I removed the tube from the plating bath to check on progress; one side of the tube had plated fairly uniformly

but the other side had a very thick and cratered deposit

Not a good start. And this was using the lowest voltage setting.

As the thick deposit was mainly on one side I checked that both the zinc anodes were connected properly, which they were. After a bit of research, I decided that for the next attempt I would remove the aquarium heater to reduce the temperature of the electrolyte. That made a huge difference and after a bit more experimentation I started plating the 17 lengths of copper pipe and the numerous brass fittings for the lubrication system. 

This proved to be quite a long and tedious job as each part has to be polished and then thoroughly scoured with abrasive paste using a toothbrush prior to plating and then carefully polished after the passivation stage. Although a packet of abrasive powder comes with the kit it is nowhere near sufficient and I use VIM, usually associated with cleaning baths and sinks in days gone by; it works extremely well and is a cheap alternative.  Polishing has to be done very carefully to avoid bending these small bore copper pipes out of shape.

As with nickel plating, I found that plating copper and steel parts to be straightforward but the plating on brass ends up thinner and it is too easy to polish through the passivated zinc layer and expose the brass below. It seems that the professional way of plating brass, which is an alloy of copper and zinc and not so easily plated, is to use a cyanide-based process but this is not an option for the amateur plater in a home workshop.

It took about 3 weeks to plate and polish all the pipes and fittings but eventually I had a box full of shiny silver-looking bits rather than copper and brass bits.

In the meantime, the powder coated parts had been finished and it was time to start reassembling the bike. I always like to get a rolling chassis built up as soon as possible as all the other bits effectively “hang off” of that. In addition to the new fork spindles and the repair to the steering head stem I also had new friction disks cut for the forks and steering damper – one on each side for the forks and one at the base of the bottom yoke for the steering damper. As I use the same company (Saftek) for all my friction materials, including clutch and brakes, I had the rear brake shoes relined at the same time. The front had already been done.

The front forks could now be reassembled and attached to the frame. I always use new ball bearings when reassembling steering heads (or any other ball race with lose balls); for the small amount of money that they cost it’s really not worth reusing the old ones. Mixing old and new balls is a definite NO as there is likely to be a slight difference in size as the older balls will have worn slightly.

The rear frame section was loosely attached at the same time and the engine plates put in place. The next job will be to put the "bottom-end" in the engine plates. The engine will be built in-situ in the frame rather than as a single entity and then “inserted” into the frame. Why? Well, there are 2 reasons: firstly, apart from 2 studs at the bottom of the crankcases, the remaining 6 (3 at the front and 3 at the rear) are sandwiched between engine plates and to ensure that the crankcases-to-crankcase seal is not broken after assembly it is better to assemble and seal the crankcases and to immediately put them into the frame and bolt up securely; secondly, the entire engine is pretty heavy and I don’t fancy trying to put it into the frame in one lump without injuring myself.

Up to this point, the crankshaft has not yet been put into the crankcases and I have relied on measurements that it will fit correctly. Before putting the assembled and sealed bottom-end into the frame various checks need to be made to ensure that everything - the crankshaft, crankcases, pistons + cylinders - actually fit together as intended.


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