SUZUKI TR750
Pegs, positioning and comfort are all that’s on Malc’s mind this month!
Malc Shaw carries on with his two-stroke
I’m quite pleased with the results with the TR750 so far, but there’s already a few bits which are not quite what I envisaged or working how I’d like. A consistent issue is how to get everything to work together as it should and in a safe way – and that means the controls.
Now I have to ‘fess’ up, age is creeping up on me and I’m no racing snake, the odd pint of real ale and bacon butties have done their best to shape the frame! As can probably be seen from earlier pics the clip-ons have a slight rise and are not halfway down the forks. There’s no way I can ride a race bike these days and some level of comfort is essential. Further to this my knees are not good, one a lot worse than the other, the result of snapping my ACL (Anterior Cruciate Ligament) at a keep-fit class! I wish I could mill up a new joint!
I’ve got to work out where I put my feet and be able to operate the controls. Thankfully, my worst knee is the rear brake side and I’ve never been a big user of the rear brake. I also struggle to push my weight up once my knee is bent; apparently that’s a result of the injury (or beer and butties?). I’ve got the sympathy vote from you I hope, but the reality of life and ergonomics are going to dictate a few things, whether I like it or not.
With the bike on a paddock stand and a towel rolled up on the seat to simulate the 50mm of padding, it was a case of positioning my feet to give me a rough idea of where the pegs needed to be. Blocks of wood were then stacked up to give me a further idea of position and what I could physically tolerate. The CMR frame has lugs already welded on to it to mount the footrest hangers. If you look at pictures of their race bikes, there is no way I could bend enough to get my feet on the pegs where they site them, but then I’ve no intention of leaning over that far anyway! I used a redundant ally plate that had a foot
peg on to give me an idea of where my datum points needed to be: this is (Photo 1) and apologies for the poor quality of the shot!
The next stage was to make a cardboard template before cutting any material. On the template I could also map out the distances and angles between the required holes. (Photo 2) This ensures that once on the mill I could use the DRO, digital readout, (Photo 3) to make sure left and right hangers are the same. I also used a bit of old box drilled at the required intervals so I had something to mount the hanger on and fix in the machine vice.
The DRO, for those of you that don’t know, gives an accurate measurement (either metric or imperial) on the X&Y axis. That’s left and right, back and forwards. (Z is up and down, but I don’t have that on that particular model). Simply, if you pick a point and zero X&Y you get a reading of 0/0, then when you move the mill table it tells you where the centre of your tool is, enabling you to make accurate and repeatable measurements.
I keep ‘in stock’ a short length of half-inch x eight-inch 6082 aluminium. This is my go-to material for making a number of components. It is classed as a medium strength structural alloy. It has good corrosion resistance, is easy to machine and has good weldability. Talk to your local stockist, they often will have ‘off-cuts’ so you don’t have to pay out for a full length. The template shape was transferred to the aluminium, then mounted on the mill bed. Holes drilled and pocketed with a cutter where required (Photo 4), then the basic shape hacked out using my cheap bandsaw. Cut slowly and use WD-40 as a lubricant to help prevent clogging on the blade.
Back on the mill, the edges were machined using a cutter. I decided it looked a bit ‘heavy’ so again with a cutter, machined out the centre. (Photo 5) The footrests and lever ends were made from stock solid round 6082 aluminium. They were turned to size, drilled and tapped so they could be fixed to the levers and a knurled finish put on them (Photo 6). I think at some point they will need to be anodized as one of my bugbears with finished aluminium is how soft it is and so easy to damage or mark.
I don’t have a formula for the brake and gear levers. I just look at what I think will work, cut out a rough shape from very thin ally sheet and see if I’m anywhere near. One part that I’ve found that seems to fit the older Suzukis is the splined gear link from a Suzuki RGV250. They are still available; mine came from Robinsons Foundry in Canterbury as they are local
and good. Again, I look at other bikes: it gives me a clue as to how things work.
The stroke on the rear brake mastercylinder rod needs to be as straight as possible; gear linkages need not to foul another component or the rider’s foot. Seems logical, but I come back to the point of how to make things work, it’s surprising how something seemingly simple can be quite tricky.
The gear and brake levers followed initially the same process as the hangers, which gave me the shape and holes in the right places. This enabled a mock fit-up to see if they functioned. Basically, I had two chunks of aluminium, which did not look very pretty. I knew I needed to slim them down, but wanted to retain some of the material where parts connected. With the hangers I had rounded the ends by hand and although ok-ish, it wasn’t as precise as I wanted.
After a bit of thinking I came to the conclusion that if something was rotated about its centre then anything at a set distance from it would scribe an arc (i.e., drawing compass). Steel bar was turned up on the lathe, threaded in the centre, then a bolt was screwed in, the head skimmed flat and a centre machined in.
(Photo 7) This, then, could be fitted into my rotary table; the centre of the part is easily found and the distance required calculated to machine the required radius. It works, but you do have to make sure it’s bolted down tight, supported, and take only small cuts. (Photo 8.)
I deliberated on what bearings to use, initially thinking phosphor bronze, but a trip to, and chat with, my local bearing supplier suggested a 10mm ID (the bolt size I wanted to use) and 26mm ID. I used a boring head in the mill to machine the hole to size after centring it, also making sure the depth was correct. With the levers back on the mill table I was able to remove the rest of the material I wanted
(Photo 9). With a bit of fine wet and dry paper the machine marks should come out relatively easily.
Spacers were made on the lathe to mount the hangers at the required distance from the frame and a couple of small ones made so the lever bearings could rotate freely when bolted up between them and the foot-peg. A length of stainless rod had left- and right-hand threads cut, one each end, and rod end bearings fitted to fine-tune the gear lever angle (Photo10). A small plate was made and welded to the brake hanger and a master-cylinder from a 1200 Bandit fitted (Photo 11).
I’m not overly happy with the fact they are so low in aesthetic terms, but there is still plenty of ground clearance. In this case, needs must has dictated the outcome. There is still refining to do before I feel they are finished and I have learnt a lot. Importantly, they now allow me to move on with the next phase of the project. There I was thinking I could put my feet up!
Thanks to: Robinsons Foundry Ltd – Suzuki Vintage Parts. 01227 454366