YAMAHA TX750
Mark is back with part 4 on this twin!
Ihave spent some time sorting peripheral engine parts (though God knows what the important internal bits are like) so now I want to turn my attention to the cycle parts.
I needed to sort out the front brake, which was completely inoperative, as well as servicing and checking the back brake. The front fork seals were leaking as one might expect and it would be a good idea to check the steering head bearings at the same time.
The forks are very simple and straightforward to overhaul. I know you can buy a special tool for this job, but my ‘special tool’ to remove the old seals (Photo 1) worked ok, as usual. It is just a pry bar with a strip of sheet steel as a backing to prevent damage to the top of the fork case. The seals are a standard size and thus it is not necessary to order specific Yamaha parts. Mine came from Simply Bearings, whose products are always good and quickly delivered.
Another not very special tool needed was a very large Allen key (Photo 2) for the top caps. You could probably make up something using a large nut and bolt, but why bother as you can get a whole set of big keys for not very much these days? Admittedly, cheap ones are not of Rolls-royce quality, but they do the job.
All the internal fork parts were in good condition and the tubes were practically like new – in fact, I could not work out if they actually could be the originals or whether they were replacements. One interesting point was that the external dust seals were also like new (Photo 3), so maybe the forks were overhauled not too long ago. The lower cases were slightly scraped (Photo 4) and I wonder what caused this? That scratch did mostly polish out using a Scotchbrite wheel.
The upper yoke was a bit messy (Photo 5) and rather than respraying it I removed the paint with stripper (Photo 6) and polished it, which to me looks a lot better. Normally I would replace steering head ball bearings with taper roller sets, but although at first they looked a bit of a mess (Photo 7) the parts were, in fact, perfectly ok so I saved the £35 or so for something more pressing.
The TX is fitted with a hydraulic steering damper, which had leaked (Photo 8), so it seemed pretty pointless refitting it. I am sure it was fitted for a purpose, but I think I shall see what the handling is like without it. It might be ok with modern tyres and just me riding. And if it is not (assuming I do not find out the hard way) I shall take the damper to bits to sort it out.
I know people make a fuss about determining the exact measurement on each fork leg between the surface of the oil and the top of the fork, but quite honestly how much difference does it make for a slow old bike like this? Yamaha specify the contents of each leg as being a rather precise 173ml, which seems more than sufficiently accurate, but how can it be measured? You could do this by using a graduated measuring cylinder, but I never quite trust these measurements after once using one that turned out to be completely wrong, messing things up. I now prefer to do it from first principles instead.
On a plain unmarked cylinder, I made a mark at the right level by simply pouring in 173 grams of water (which occupies almost exactly 173ml). You do not need laboratory equipment to do this as you can do it very simply with digital kitchen scales, which are very accurate and inexpensive now. Then tip out the water, carefully wipe the cylinder dry and replace it with the oil (Photo 9).
The front brake caliper is the same as that on the TX500 and a few other contemporary Yamahas. It was in pretty good shape, but of course needed new seals, which are of a very simple design (Photo 10). The material is cast iron so you can be fairly forceful when cleaning it up. The outside was quite acceptable and even had the original blobs of yellow paint on the bolts, showing that they had been correctly tightened at the factory (Photo 11). I took this photo, by the way, to remind myself which way round the anti-squeal shims were fitted. EBC pads were probably a better solution than ancient NOS Yamaha items (Photo 12).
One discovery I made (by reading the manual properly) was that it is just possible to take the caliper off with the wheel and mudguard in place (Photo 13), which had not occurred to me before. The reason why the brake would not work was that there was not enough brown goo in the master cylinder (Photo 14), but it was easy enough to see where it had gone (Photo 15). Obviously an overhaul was required, but when it came to getting hold of spare parts I happened to notice that the cylinder looked identical to that on the
CB750 (Photo 16) – apart from the screw-on cap— so if it was the same on the outside, maybe it would also be on the inside? An investigation of the relevant parts books showed that this did seem to be the case so logically I should be able to use easier-to-find CB750 parts for it. After removing the internal parts they really did look the same. The conclusion then was that Honda and Yamaha used the same external supplier for the master cylinders, presumably Tokico.
Genuine Honda brake parts are very expensive, but I have always had perfect success with good-quality pattern parts. I got this Japanese-made Tourmax set (Photo 17), which was meant to fit a CB750, but worked perfectly for this application.
One thing I want to draw your attention to is shown in Photo 18. Here we see the two holes at the bottom of the master cylinder reservoir: a big one and a small one. The master cylinder will not work properly if either one is blocked. A carburettor jet reaming tool works well on the small hole.
Next time I have a closer look at the braking system.