YAMAHA DT175
Ralph Ferrand buys another little restoration. Class!
While taking my wife’s Z650 for an MOT I noticed a very forlorn looking DT that clearly hadn’t turned a wheel in years leaning up against a wall. I am a sucker for wanting to rescue bikes that clearly are a lost hope, so asked the owner how little he would accept for it to have a new home. I obviously had my rose tinted glasses on and could only see what it could look like rather than the stark reality. This fool was soon parted from his money and in more trouble with my wife; I had promised I would finish restoring my RD250B that I had long since lost interest in, before even thinking about buying another wreck. I had anticipated her lack of enthusiasm for the little Yamaha, but the deal had been done and I had paid fifty quid more than I wanted to, by losing the toss of a coin. When I announced to my friends that I had bought a DT250 for three hundred notes there was great admiration from all sides, and even more so when I realised it wasn’t a 250 at all but a 175 that had been misrepresented; apparently the 175 is far better and more valuable. By the time I had got it home in the van, the scales came away from my eyes and I started to realise what a pile of crap I had bought and that it was clearly going to cost a fortune to put right. For some perverse reason, this didn’t seem to dampen my enthusiasm for the dinky trail bike, and I soon started to strip it to its component parts. What is curious is that the rear swingarm seems to have been extended and in a reasonably competent way. I don’t know much about dirt bikes, but I can only assume that it was done to dissuade it from sticking its front wheel in the air, though I wouldn’t have thought a tiny 175cc engine would have an untrainable propensity for such behaviour. The wiring looked pretty shaky, so I guess that’ll be another loom to make, but are automotive fuses really so expensive that one feels the need to use a domestic
13amp fuse from a plug top? With the tinted glasses on, the wheels didn’t look too bad – nothing that a bit of chrome cleaner couldn’t sort out: ’tis a dirt bike after all. The tyres were an absolute nightmare to remove as they were literally stuck with rust to the rims. Once I had removed the economy rim tape (gaffer tape) the full horror was unveiled; there were actually holes in the rims and I don’t mean for the tyre valves! I wanted to undo at least one spoke of each size as a pattern for replacements, but so heavy was the corrosion that there were only two tools for the job and as I couldn’t find my bolt croppers it was the angle grinder!
Neither brake drum was in a pretty shape either, so I had to machine them out in the lathe. I managed to set the rear drum between the live centre of the headstock and a revolving tail stock centre and drove the drum using a bolt I fitted into the driving plate against one of the sprocket studs. While it did ‘sing’ a bit I managed to get an acceptable finish, though breaking through the cast iron ‘chill’ wasn’t easy. With the operation of the friction materials of the brake shoe against the iron during braking, heat is built up which ‘heat treats’ the drum, making the surface very much harder than the material underneath. This is the same effect one
gets when machining iron castings and the hard surface is known as chill. Once through this hard casing, cast iron is fairly soft and nice to machine, but the chill will take the edge off even quality tungsten carbide tools. As there was no way to ‘drive’ the front hub between centres, I gripped one side in reverse jaws in the three jaw chuck and used the revolving centre in the bearing on the other side with the tailstock to keep it all true. When machining pretty much any metal it is best to use cutting oil, which will extend the life of your tools, be they taps, dies, drills or lathe tools. These days I use what we used to call throwaway tip tools, but seem to be called index-able tools