HONDA CB750 K2
Mark Haycock finally sorts his chain and sprockets!
We are now ready to fit the new chain to the CB750, and I shall take a look at a couple of very reasonably priced tools to facilitate this. First though, before putting back the cover over the front sprocket, I did notice that the electrical connections in this area (Photo 1) were not in great condition as the insulation must have shrunk after being heated by the engine for years, exposing the conductors, so I wrapped them with extra insulation in the form of non-sticky plastic tape: best to sort this out now, rather than by the side of the road. The chain in the kit was supplied as being the correct size and length for the application so I was a little surprised to find that it was actually too long and so it would need to be shortened to suit. Also I should point out that time has moved on and the old-fashioned spring link originally used on CB750S (and everything else come to that) is now regarded as insecure and hence unsatisfactory. The recommended way now is to use a riveted link and everything you need should be included within a kit such as this. In the past I simply used an angle grinder to shorten chains and did the riveting for joining by hand and this worked okay, but I decided to ‘get with it’ and buy the proper equipment. What put me off before was the price of the kit which I would rarely use, but things have changed and now you can apparently buy the tool you need for a tenner, in fact, here it is (Photo 2). Even I am not that stingy. Sounds remarkably cheap, but does it work? I have seen a few reviews of this tool which were somewhat less than glowing, but let us see. The first thing that struck me was that it came with no instructions whatsoever, which strikes me as an odd omission. Anyway, I knew what to do, so having checked how much chain I needed to remove (Photo 3) I could dive straight in and push the relevant rivet through. Really though, this was probably asking a bit much for a cheap little tool like this so to give it a bit of leeway it is best to remove the end of the rivet with an angle grinder as in Photo 4. I try to do grinding outside if possible as I feel that the abrasive dust flying everywhere is best not combined with engine internals from other projects. Because the holding handle for the tool was a bit feeble looking, the whole thing needed to be held in a vice and it was more convenient to use the Workmate and here it is, part done (Photo 5). There are one or two points about what we see here. One reviewer said that he had managed to bend the pin as it was inserted to push out the rivet. This tendency to bend can be at least reduced by grinding off the rivet as we saw but also by arranging things to minimise the extension of the pin,
especially to start with. I have also seen complaints that the threads are a rather poor fit and that is quite true. This makes it difficult to ensure that the pin is in precisely the right position. I packed the threads with PTFE tape to tighten the fit but I don’t know if it made much difference really. Finally, note that the tightening to press out the rivet should be done using the bigger thread: the small one is just to position the pin. The great news was that the pin did not bend and the tool worked perfectly. I had some bits of chain left over which I kept just in case – well, you never know, do you? Now we come to joining the shortened chain. DID are very particular that the components of the joining link should be well lubricated and they of course provide the correct grease as well as the four O-rings you need (Photo 6). And here is the joining link assembled, ready to be pressed together (Photo 7). This is done using these two plates (Photo 8) as the parts fit quite tightly. The difficulty here is that the side-plate needs to be pressed on far enough, but not too far so that it starts to bind and thus is reluctant to bend around the sprocket. You can assess the correct position by measuring the chain width using a caliper on another link and making the joining link the same. Then the O-rings (you did put all four of the O-rings in place, didn’t you?) are just being lightly pressed and will seal without being flattened. And you will end up with something like this (Photo 9). Now we are ready to expand the end of the rivet. In the CB750 manual Honda recommend using a flat chisel-shaped punch to form a cross at the end, but the DID joint rivets and tool here are set up to use a pointed punch to open out the hollow end in a circular form. The rivets I removed to split the chain were shaped like this (Photo 10) and you can see that they are expanded at the end by just a very small amount. It is safer to expand the softer joining rivets by a little more than this; an increase of about 0.7mm in diameter is okay. By expanding the end by too much though, you are not making it even safer: quite the reverse as the expanded part is then too thin and it is thus weaker.
Now the big test: is this cheap tool strong enough to expand the rivet properly? The attachments they give you are shown in Photo 11. My first thoughts were that the shaping tool was not formed correctly to work and so it proved. After tightening the screw as much as I dared, the rivet had not changed. So I ground the end down to a more pointed shape as in Photo 12. Same result, because the tool was apparently softer than the rivet. The conclusion must be that the complete tool as supplied is not capable of fitting a new chain (of this size, anyway) but to be fair it did okay at splitting the old one so for less than a tenner it could be of some use. So the next step was to buy an even more expensive chain tool and here it is (Photo 13), price £15. This is a much more substantial-looking set-up and I had high hopes for it. Photo 14 shows it ready to use and you can see that (1) the handle is actually substantial enough to grab hold of and (2) the part which expands the rivet is a ball bearing, which of course is hard enough to do the job. It worked perfectly, and Photo 15 shows the result on the first rivet. I couldn’t complain about that (well, the chain hasn’t fallen off yet) and it was considerably cheaper than the genuine DID, or any other, professional tool. So is it worth spending £100 or more for a single professional-standard, one-task tool which is rarely used? Well, if you have any sense, probably not. But paying to get someone else to do this work is now very expensive. So why not have a go with something cheaper which will do the job and is fine for occasional use?