HONDA CB750 K2
More issues have been found with the Yank-spec K2; this time it’s the electrics!
Mark Haycock gets on with the electrics. What does he find?
In common with every other bike project I have worked on, the K2’s wiring needed a little attention, well, quite a lot of attention actually! We saw last time that I gave the engine a once-over just to make sure that it was in a condition where I could reasonably expect it to work, and now it was time to do the same thing for the electrics. The first item that caught my eye was the remains of the fuse box (Photo 1). Judging by the connections to the fuse I think they had perhaps been a little overloaded. One of the improvements which came with the later K3 model was a better fuse arrangement, with no fewer than three of them. But the K2 makes do with a single one, meaning that a fault in something of relatively minor importance can knock out the entire electrical system, leading to an unscheduled stop on an unlit country road at night – it always seems to work that way. I did think about rewiring the whole bike to incorporate the K3 improvements but decided instead that a few in-line fuses could be used at various points instead. In-line holders for blade type fuses cost practically nothing on ebay and are very handy. Photo 2 shows a couple I installed for the main and indicator fuses. Elsewhere were the usual signs of age and damp storage as many of the electrical connectors were corroded (Photo 3). It is easy enough to attend to the male connectors with a bit of wet & dry but the females are a bit more difficult. I use a fine round needle file. The old-fashioned electro-mechanical Hitachi voltage regulator (which works perfectly well in my experience) needed its connections touched up (Photo 4). Note how helpful they have been in not only showing the colour of the wires but also their function: E (earth), F (field) and L (live).
Some of the K2 wiring is a little idiosyncratic as you can see in Photo 5. As you can also see, the connections include brown to green, black to red (sometimes) and black to green (for a bit). Some connections are a little temporarylooking (Photo 6). Yes, okay, I needed to do a fair bit of sorting after a home electrician had been let loose. The battery connections were beyond refurbishment (Photo 7) so I knocked up some replacements with some aircraft cables I have in stock (Photo 8). By using three smaller gauge wires rather than one thick one, I hoped to make the complete cable more flexible, but by the time I had wrapped them they were not that easy to bend I must admit. The flexible conduit containing the main run of wires to the headlamp had stopped being flexible years before (Photo 9) and in cutting it off I made a slight error (Photo 10). Oh well. Rather than using conduit I again wrapped the wires with non-sticky tape, finishing the ends with small pieces of self-incorporating rubber tape (Photo 11). The main (ignition) switch carries all the current required for the electrical system, so it is a good idea to make sure it is up to the job. Mine was not as the red wire did not appear to have been soldered on properly (Photo 12). Clearly, it cannot have left the factory like that. To re-do the soldering it is best to dismantle the switch and it is often an idea to do this anyway as the contacts do become corroded after years of inactivity. It is easy enough to do on these old Honda switches as the electrical parts are held on to the lock section simply by three swages which can be straightened out. The contents were not a pretty sight (Photo 13). Although the various parts could be cleaned up, one significant fault was that one of the contacts had overheated, no doubt from the soldering repair (Photo 14). I have collected a few similar switches over the years (Photo 15), so maybe I could use one of the spares, or at least assemble a reasonable switch from the parts? The short answer was no, as the main problem was that although the electrical parts could be found, the locks were all worn out. I did find a pattern switch on ebay, incredibly cheap at about £12, and this did work okay though I do not think it is quite as secure as the original but will do for now. For some reason, a previous owner had removed the indicators and naturally I wanted to replace them, so I was pleased to find a set of what was claimed to be genuine Stanley items for about £50. Looking at them, they seemed to be pretty good copies with a couple of reservations. Firstly, the wiring was not of the original pattern, though that could be modified to fit. Worse was the fact that the indicator bodies did not fit in the genuine Honda arms (Photo 16). I did try to help the fitting process with a gentle tap using a soft hammer, but this was a bad idea (Photo 17). Nothing a spot of epoxy could not fix though. To make them fit I found that it was a lot easier to file the splines of the arms than those within the indicator bodies, and in fact they were held perfectly securely without the splines.
The curious thing was that the indicators worked perfectly okay when tested but later there was nothing. It seemed most likely that the switch was at fault as this relies on ancient moveable contacts and thus it must be at least one of the most vulnerable parts of the indicators’ electrical system. I have fixed Honda handlebar switches quite a few times over the years and all that is usually necessary is to clean up the sliding contacts. You have to be extremely careful not to lose tiny components such as springs and ball bearings (the latter are used as detents to encourage the switch to stay within fixed positions, i.e. off or on rather than somewhere in between. Unfortunately, this one defeated me rather: it relied on fitting a small block of nylon, complete with two springs, a sliding contact and a ball bearing all at once into the switch body, which I found to be impossible. I did try various methods to hold bits in place and to fit bits after assembly of the rest, but eventually had to compromise by missing out the ball bearing. This meant that the detent was not as positive as it should have been, which is workable but not ideal, and I shall need to revisit that later on. But the point was, cleaning the switch did not fix the problem. It was actually that the flasher unit had failed. There is a slight curiosity here, and it is that the American spec bikes have a small electronic unit (Photo 18), but bikes for the rest of the world used an old fashioned electro-mechanical canister type. This was because American bikes had a buzzer which worked with the indicators, to act as a warning to other road users as well as the rider that the indicators were in operation. There was a complication in that an extra button was fitted to the handlebar switch (Photo 19), and this was used to cancel the buzzer when required, meaning that the electrical load could vary. Electronic flasher units are not as sensitive as electro-mechanical ones to load, the problem being that the flashing speed would vary using the older type. The electronic type has only two wires, but the canister had an earth too and this explains why the American bikes had a superfluous earth wire nearby (Photo 20). I admit that on occasions I have forgotten to cancel the indicators so as my bike had no buzzer fitted I bought a new electronic unit complete with buzzer. If I get fed up with the noise I can block it up to stop it sounding. The last issue was with the headlamp. In common with many other American market vehicles of that era, the K2 was fitted with a sealed beam lighting unit. This means that the whole unit acts like a giant bulb in that the filaments are mounted at the optical centre and the whole unit is evacuated and inert gas filled. I think the advantage of this was meant to be that the unit was focussed correctly, as some contemporary bulbs were not well made. The disadvantage is that you are stuck with old-fashioned plain filaments rather than quartz halogen and the light output is poor. The other issue in this case was that the unit dipped to the right instead of the left, but it is possible to pass MOT requirements by sticking a piece of black tape on the right place on the glass. Unfortunately though, the unit was not usable as despite being working, a piece of the filament holder had detached and was jangling around inside. It would only be a matter of time before it hit a filament so it was best to replace the whole unit with a new UK standard unit equipped with a quartz halogen bulb, which was not too exorbitant from David Silver. There were quite a few components holding the unit in place so it made life easier to photo the dismantling process and mark the components to make sure they got put back in the same relationship (Photo 21). More next time!