1952 Sunbeam S8 – Resurrection

Part Three of Four – Cycle Parts

It was at this point that my interest turned to the frame and the other cycle parts. All of the black parts, including the frame, had been powder coated and carefully wrapped in protective sheeting. As I said at the start of Part One of this article, not all of the parts had been well prepared before they were coated. The battery box, the electrics box and the tool box were all dented or distorted to some degree. Some of the threads and working surfaces had been plugged or masked but others had not. That meant that a lot of time was spent scraping, grinding or filing the coating from places where it was not required, e.g. the spindle holes in the fork sliders, the bearing cups in the head-stock and un-clogging threads with taps or dies.

I set about cleaning-up the parts and rectifying damage where practical. There are limits to the extent to which metal can be bent into shape after it has been powder coated. Some repairs were successful but some, like the nasty dent on the bottom corner of the battery box, had to be left alone for fear of doing more harm than good.

There was no option, however, but to send the frame off to have it straightened, after which it would be stripped and re-finished. The small firm that did the straightening, Maidstone Motoliner, did a brilliant job. They used factory drawings and measurements to get within a millimetre of spot-on. Their accuracy exceeds that of the frames that came out of the Sunbeam factory. Not only does that make it easier to align the lugs for the engine mounts and cycle parts but it means that the bike will handle very nicely.

However, before the frame could be sent off, the rear suspension units and the rear drive had to be temporarily assembled onto the frame and the rear wheel fitted. The reason for that is to provide a reference for taking accurate measurements and for aligning the head-stock in the same vertical plane as the rear wheel. It is a process that requires a lot of heat, brute force, patience and skill.

Having the frame straightened slowed progress but did not stop it altogether because there was useful work to be done preparing and assembling the forks and repairing the centre-stand, side-stand and distributor, among other things.

The side-stand was badly bent, which had caused the peg that anchors the return spring to become dislodged. Straightening the leg required lots of heat and replacing the peg was another brazing job, having first made a new peg on the lathe. The area of extreme wear on the foot of the stand was then restored to its original thickness by building it up with weld material, using a MiG welder, and dressing it back to shape. The kind of heat that can melt bronze and make iron or steel sufficiently malleable to bend it without severely weakening it will destroy powder coat in seconds. Therefore it would be necessary to clean the remnants of the finish from the affected parts and have them powder coated again.

The right-hand leg of the centre-stand was badly bent and twisted, possibly during the collision that bent the frame. The left-hand leg was missing the peg that assists with deploying and folding the stand. That peg is often missing and replacing it is a repair that I do frequently. Using the centre-stand without that peg is quite irritating. The centre-stand legs are substantial and straightening them required quite a lot of heat to get it to a bright red colour, and considerable force.

The heat was provided by an oxyacetylene torch and the force was provided by a combination of a heavy engineering vice, an improvised lever, an anvil and a big hammer. The right-hand leg had to be drilled to remove the remnant of the broken peg. A new peg was made from silver steel rod (mild steel is not strong enough) and brazed into the leg using oxyacetylene. Finally, the bottoms of the feet were built up with weld material to restore the metal that had been worn away.

The distributor was corroded and dirty, which warranted closer examination of its internal components. Dismantling it revealed that the weight plate was a little loose on its shaft, the bronze bush was worn and the steel components were corroded. The old bush and oil seal were pulled out and new ones fitted. The joint between the shaft and the weight plate was brazed to fix it permanently to the shaft.

The corrosion was removed from the distributor body by brushing and then polishing on a polishing wheel. The points were refaced with a fine file and the distributor re-assembled and tested. This bike was destined to have a wasted-spark ignition system and a dual-output coil fitted so the rotor arm could be discarded and a dummy distributor cap fitted.

The fork sliders had a lot of sludge and grit in the bottom and the stanchions had some surface corrosion and slight irregularities, so some cleaning and smoothing was called for. The bronze bushes and seals were all quite worn so new ones were fitted and the fork legs assembled and checked to ensure that they would slide smoothly.

The air filter was rusty and a bit knocked about. The rust was dealt with by bathing the steel components in rust treatment solution, after which it was washed and straightened using a hammer and anvil. Priming with red oxide paint and finishing in gloss black paint restored it to its former glory.

The rear number plate bracket had been powder coated and a new rear light fitting was included in the inventory. A new rectangular number plate was ordered for the rear and two curved plates were ordered for the front mudguard. The light fitting, reflector and number plate where assembled onto the number plate bracket.

Also in the inventory were two new baffle pipes, a new flexible exhaust section and new down-pipes. The silencer was in excellent condition and had been polished. Assembly of the exhaust system was straightforward but required the usual adjustment of the joints with shim material, to eliminate gas leaks. The joints in Sunbeam exhaust pipes seldom seem to seal properly without shimming.

By the time those jobs were completed, the frame was ready for collection from the straightener but it still needed to be cleaned and prepared for powder coating. In particular, the rear wheel, suspension components and the rear drive all needed to be removed so that a bare frame could be delivered to the finisher. Because the powder coat had been damaged by the heat, it had to be stripped in a chemical bath before the whole frame could be re-finished in powder coat.

There was an original Lucas Altette horn of the correct type in the inventory but testing it with a battery showed that it wasn't working. Dismantling it and cleaning the contacts was enough to get it going again and a little bit of adjustment had it performing as it should. All that was needed was some paint, a new bezel and a new set of chrome dome nuts to restore its youthful appearance. I followed that by refurbishing some other small components, including the Layrub coupling and the two warning lights. The speedometer was not working properly so I took it to a local Smiths Chronometric specialist, who I have used on numerous occasions, for refurbishing and for him to replace some parts that were missing.

At this point in the rebuild, a discussion with the owner led to the conclusion that the powder coating finish on the fuel tank and the mudguards was not of an acceptable standard and should be replaced with a wet paint finish rather than the dry coating. This would provide an opportunity to strip them back to bare metal and prepare the surface properly with etch primer and repair the blemishes before painting and varnishing. Although this would give a much better result, it would also involve considerable additional cost, so it made sense to check that the tank was completely sound and the mudguards would fit perfectly.

So, threaded plugs were used to seal the holes in the tank where the fuel taps had been and the filler hole was closed with a specially adapted cap with an air feed to facilitate pressurisation of the tank with compressed air to test for leaks. There isn't much satisfaction in spending money on painting a tank only to discover later that it leaks. Similarly, it is a good idea to make sure that if any modifications are needed to the mudguards then they are carried out before they are painted.

It was during these checks that another erroneous assumption, on my part, came to light. I had expected that a rear mudguard that had been removed from an S8 was an S8 mudguard. In fact, it was an S7 mudguard. Like the frame, it came wrapped in protective sheeting and I felt no pressing need to disturb it until it was needed. In hindsight, I should have checked it on arrival.

Even though an S7 mudguard will fit an S8 frame, which is essentially the same as an S7 frame, the lower section of mudguard was an original S8 part, which will not mate with an S7 upper section. A discussion with the owner led to the conclusion that a decent S8 mudguard needed to be found.

After some research, I found a fairly local small company that claimed to be capable of fabricating a new mudguard from scratch. Seeing some examples of their previous work gave me some confidence. They needed a pattern to work from so I lent them another sound mudguard, from my own S8, for them to copy. Much elapsed time and many excuses later, it started to become clear that they were unlikely to fulfil their promise. I was unable to locate an alternative fabricator at the time (I have found two since) so I started looking for other viable options. The most cost-effective of those was to buy a sound second-hand one, repair it and have it painted.

A reasonable one was sourced from Stewart Engineering. It needed to be modified a little to make it fit onto the lower section of mudguard and it needed to have some areas of corrosion cut out and some new steel patches shaped and welded in. It then needed a bit of filling and smoothing but it was the right shape and it was reasonably sound. The restored rear mudguard then needed to be primed, painted and lacquered but that would have been necessary in any case.

Incidentally, the upper and lower sections of the rear mudguard were made in the factory as a matching pair. If you try to use two sections from different bikes, they generally won't fit together very well. One or other, or both, of them will probably need to be modified, which isn't particularly straightforward owing to the proximity of the hinge brackets, which are riveted in place.

The finisher contacted me to let me know that the frame and the other cycle parts, that had been sent to him earlier for powder coating, were ready for collection, so I went to pick them up. Careful masking had ensured that there wasn't much cleaning-up to do but there were a few lugs that needed to be reamed to clear away excess coating.

Now that I had the frame and a reasonably complete set of restored cycle parts, reassembly of the rolling chassis could start. I always like to start by fixing the centre-stand and side-stand in place. The rear suspension and rear drive are the most logical items to fit next. Then I can fit the rear wheel to support the frame on the wheel and the centre stand in its natural attitude. During assembly, I lubricate the pillars, sliders and springs of the rear plungers liberally with molybdenum disulphide grease. You could use almost any grease but 'moly' is good in cases where frequent lubrication may be neglected. It contains a persistent residual lubricant that continues to work even if the grease starts to dry out.

I Then fitted the upper and lower fork yokes, their ball bearings, the steering damper assembly and the upper shrouds. I passed the assembled fork legs, with springs lubricated and fitted, through the yokes and secured them in place with the top caps. I leave the top yoke clamp and the two lower yoke clamps loose until I have made sure that the forks are straight by dry-fitting the front wheel spindle and measuring the distance between the legs at various points, to ensure that they are parallel. Then I tighten the clamps and fit the front wheel and brake plate, at which point I have something that is stable and begins to look like a bike.

The order in which I prefer to proceed from this point varies but, on this occasion it was expedient to fit the lower rear mudguard section and to assemble and test the complete rear brake linkage.

The 'U' shaped fork brace was clearly a victim of the crash that had bent the frame. It needed to be restored to its original symmetrical shape before it could be fitted to the fork sliders. Then the frame bracing bar, front engine snubbers and rear engine/gearbox mounting plate were fitted to the frame in preparation to receive the engine. But before the engine could be lifted in, the frame rails had to be protected against damage to the finish from contact with the engine. I use foam tubing that has a tough plastic membrane on its outer surface and I tape it to the frame. In cases where the lower rear mudguard is already in place, I also protect it with a strong plastic tape with low-tack adhesive, which protects against accidental contact but does not risk spoiling the finish when it is peeled off.

In the fourth and final part, I celebrate the emergence of a rather nice working motorcycle from a stack of crates.