❙ SUZUKI TR750
Malcolm finds out that inspiration and preparation help when the devil is in the detail.
Malc Shaw gets to grips with a sprocket cover.
Iknow it could be some time before you read this, as I’m well ahead, but as I’m tapping away at this it’s late Jan and down in Kent we are in Lockdown and in tier 5.
Sadly, in December I heard the terrible news that Denis Curtis of CMR had passed away. His wife had emailed me to let me know. Denis was a former racer and consummate engineer; a man who was passionate about his work. His frames are used in classic racing by a lot of top teams and riders around the world. CMR will continue for the foreseeable future with Denis’s right-hand man, Byron, whom he imbued with his knowledge and skills and Denis’s wife Lindi, running the business. Take some time to check out the CMR website and Denis’s history, an extremely talented individual who will be sadly missed.
On a personal note, Denis had always been helpful and interested in my build, receiving regular updates and photographs, replying with encouragement and constructive comments. We had talked about possibly meeting up at an IOM Classic TT with my TR but that now, sadly, will never happen.
As they say, time waits for no man and I’ve plenty to get on with. I’ve now half a rebuilt engine sitting there, which it’s going to do for some time. I don’t want to add much more to it at present; the thought being it will be easier to manhandle and eventually mount in the frame. However, there’s nothing stopping me making a few more bits!
I wanted something to cover the sprocket area and I thought about using the standard cover by drilling some
‘racing’ holes in it! There are two casings in this area which butt up to the front casing which I’d already cut down a bit to increase clearance for the exhaust. The inner casing I could see would look aesthetically more pleasing and ‘right’, i.e. it fits the bike better if I reshaped it to follow the frame shape.
It was simply a case of fitting it up on the dummy engine in the frame, looking at the lines, marking out with a Sharpie, (they seem to write on most materials), making sure all the fixing points were maintained, then cutting it to shape with an angle grinder and 1mm cutting disc. The cut edges were finished up with a file and emery cloth to get a good finish.
The outer casing now wasn’t looking ‘right’ and I was not going to drill holes in a perfectly good casing. I used it to scribe round some ally sheet I had lying about, which closed off the ‘hole’ where the sprocket was, but I was still not happy with it. I then drilled ‘speed holes’ in it! Realising once bolted up the holes, although straight, were not in the right plane (photo 1), anyways I was not happy: it looked crap!
At that point I gave up and left it for a bit, whatever I needed was not coming. Inspiration finally came when I was looking at some pictures of TRS and the dry clutch set up left-hand side casing. I hacked up my former ‘cover’ to the shape I wanted, ignoring the holes and decided it might just work.
I scribed round the Suzuki outer casing on a piece of half-inch thick 6082 aluminium (it’s what I had), using this to mark the bolt holes, then marked round ‘my’ cover lining up the mounting holes. Over to the band-saw and I removed the excess material (photo 2). Next step was to mount it on the mill and drill the required holes (photo 3). Once done a trial fit up suggested the basic position was correct (photo 4). On the reverse side I marked out where the inner casing was as a reference (photo 5).
Having learnt from my first aborted attempt, I drilled and tapped another piece of aluminium to the distances of the cover bolt holes. This meant I could mount my work piece in the mill, keeping it ‘square’ each time I moved it (photo 6).
Cut lines were scribed out on the aluminium to give me an indication of where to machine, then back on the mill using a large cutter to machine the holes at the corners and a smaller cutter to remove the rest of the material (photo 7) and clean up all the edges. It looked a bit ‘heavy’ so back on to the mill and some countersunk fast light weight racing (they are a bit BS) holes fashioned (photo 8). Another fit up (photo 9).
It required some shaping which I did by hand, blending the shape and the corners. In my opinion there are a few things you can do which makes a real difference to the finished look of a part. That is, round
edges and corners, blend surfaces in, achieve a good fit and if you can, ‘decorate’, i.e. holes, machined lines, knurling, etc.; look at all the details the manufacturers go to on the small parts on your bike.
I think a lot about finishes and as the bike’s evolved I’ve moved closer to realising I wanted more of a ‘racer’ look, but it has to be a good finish. To some degree I’ve gone off polished aluminium, I feel a bit like it’s the preserve of the custom world and although many restorations of our beloved 70s bikes look stunning they were never like that from the factory or even when we rode them! I was going to polish the block and head but started to like the vapour blasted look; my engine casings are also vapour blasted but a bit shinier. I confess, polished ally marks easily and I do not want to be forever trying to keep a shine on it.
A while ago in CMM there was an article on Electrostatic Magic, who supply home powder-coating kits. I thought back then it would be really useful so I could do small parts when needed. I contacted them and had a helpful conversation with them following which I duly bought a kit and various powders. I reckon once you’ve done around 20 small parts you’re possibly at break-even point financially, against taking them to your local powder-coater. They have been a good company to deal with, check out their website (www. electrostaticmagic.co.uk). I’ve done a number of parts with this kit and am very pleased with the results, but as with everything I am learning along the way.
A friend who was fitting a new kitchen donated his electric cooker (better than what’s in my house, cheers Richard). And I made a small spray booth from some melamine covered MDF (photo 10). You don’t need high psi or cfm, so a small compressor will do and you basically just puff the powder on. It’s a polyester which cures under heat to give a fairly durable finish. You need to get an even coat of powder which comes with a bit of practice and the tricky bit is transferring it from my ‘booth’ to the oven, steady hand and long nose pliers required! It bakes at 180 degrees C for 10 minutes and you can actually see the powder melt and flow.
Preparation of the part as with any painting is key. First degrease and remove any loose paint/corrosion. Flatting back to remove any scratches or nasty marks is required, then I blast the parts with a fine aluminium oxide grit. It goes without saying that all grease and contaminants must be removed, so a good wash down with thinners or acetone is required. I’ve also found a ‘pre bake’ can help to remove oil that has impregnated engine casings; larger parts seem to benefit from a bit of a warm-up before coating. A wipe over before coating with a tack cloth can also help to remove any foreign particles. One tip is, JB Weld appears to withstand the heat cycle and coats okay.
I’ve decided on Titanium for my casings. It has a nice sparkle to it and is brighter than the aluminium powder. There we are, fitted up fresh from the oven, piece of cake! (photo 11).