Chain reactions!
When the chain starts to rub on certain things, what does our Male do? Apply some ingenuity!
Lasttime I'd lined up the wheels and got the chain to run fairly true with a lot of measuring and a bit of machining.
As a slight aside a mate of mine uses long fluorescent tubes as straight edges to align his wheels. He does a lot of track days and is quick, so although it's not a method I've come across before I can see how it works. At some point I'm going to investigate how I can use my Dewalt laser level to achieve this function and report back if it's successful. There're a lot of much cheaper lasers on the market and it may be a way of making a useful tool.
The chain run was clearly a problem, laying on the gear-shaft, catching on the frame and also only just clearing the rear shock (main photo.) Chain sized marks (Photo 1) could be seen on the shaft, so my guess is in the past a slack chain on the Kettle had not been attended to and
had left its impression. Another shaft I have has the same marks so maybe it's a common problem?
With the chain tightened it just clears the shaft, but still runs on the frame. At this juncture it is difficult to tell accurately where everything is going to touch. However, as the suspension compresses the situation improves.. slightly!
I needed some advice. An e-mail to Denis Curtis at CMR got the reply, ' Welcome to the world of classic racing'! A call to Pete O'dell informed me that it was a common problem, but talk of 'sleeving the shaft' (answers on a postcard) gave rise to an idea. Someone else regarding the shock issue said, ' Move it over'.
I tend to not rush, but try and think things through. I did not want to move the shocks out as I was sure this was not a good solution and clearly there're a number of CMR TRS out there, so if this is an issue then surely it would have been addressed. The other thing I keep in mind is that mainstream manufacturers spend millions on developing their bikes. I look a lot at other bikes for parts and ideas, so why re-invent the wheel?
I had a piece of solid round nylon; this is interesting to machine as it ' melts' if cut too fast. It's also tricky to get a good finish on it. A friend who has a CNC tool-making business suggests using an air-line as a 'coolant', which can work to improve machining and finish. I made a simple sleeve which rotates quite easily (photo 2) to go over the shaft and held in place between the casings. For those of you that are interested I've also found that the specific turning inserts for aluminium (photo 3) seam to work well on these kind of plastics.
Pondering the issue of the chain touching the frame, my mind wandered to trials/motocross bikes and more to the point, a chain tensioner. This looked like a potential solution, but didn't sit quite right. The answer was right under my nose!
My work bike was a Yamaha XT660X supermoto: great for getting through the morning traffic and a fun ride. (I have toured Scotland on it as well.) This bike has a little jockey wheel on the frame, which the chain runs on. My conclusion was, if this is how Yamaha designed this, it must work. No trying to find clever materials or a solution for the problem, copy and innovate!
Fowlers have a tremendous website compromising of parts books for lots of bikes. It did not take much to find the part, which thankfully is still available and not a silly price. It was duly ordered and delivered quickly.
The wheel is a strange material. It's sort of like a firm sponge, but with a harder outer (photo 4). Looking at my XT, there's no appreciable wear, yet the chain seams to run consistently on it. I've no idea what it is made of, but Yamaha do, so thanks goes to their R&D department!
A couple of bits of mild steel were shaped up to make a mounting for the wheel; a hole drilled for the bolt and to make life easy the nut welded on the back. A trick here is to make parts like this 'clamp together'. They then are basically mirror images of each other and any shape or holes line up. These were then positioned on the frame (photo 5) and tacked in place using a spacer just slightly wider than the wheel so when fitted it could rotate freely. It works, or we'll certainly find out if it does when the bike actually runs! (photo 6)
That seems like a fairly simple solution and one I'm quite pleased with, even if I do feel like I'm giving away a state secret. With something like this a lot of time goes into figuring out the solution, finding what will work rather than the actual making of the part.
CMR supply a chain-slider on the top of the swing arm: essentially a piece of flat white plastic. Its functional and intended for what the bike is primarily designed for, that's racing. I wanted something that was a little nicer and black in colour. Something that I find interesting is different materials and their use. However, it is a bewildering subject as there are so many types with specific applications. Chatting to people in varying businesses often provides information that is valuable, especially as they have knowledge and, importantly, understanding of its use. My friend the CNC tool maker suggested a material called Delrin® (Dupont). Delrin® is an engineering plastic, polyoxymethylene (POM). It has a number of properties, but the ones that lend itself to a chain-slider are high mechanical strength, stiffness and hardness. Ease of machining; resistant to chemicals; unaffected by solvents and fuels; high lubricity, which contributes to high abrasion resistance; and low co efficient of friction. Sound useful? An offcut was gratefully received. It cuts and machines really nicely. I set a piece up in the mill and used HSS cutters. Finish and end result were very pleasing (photo 7 and 8). As an extra, the process has allowed me to develop my skills on the mill without fear of wrecking my tooling, and has added to my knowledge in a number of ways. Finally, CMR had also supplied a 'shark's' fin' -you can see why it's called this. It didn't quite go where I wanted and I felt it needed to be closer to the chain. This was achieved by making a cardboard template first then transferring this to ally sheet once I was happy with the shape. Use of a cheap band-saw with a decent blade had the shape cut and fixed to the swing arm. I then turned up a further piece of nylon and threaded it in the centre so it can easily be fixed to the shark fin. It still needs a bit of work to finish it off, but the basics are there. (photo 9) The shock absorbers were an old pair of Kawasaki aftermarket upgrades. They were never intended to be used so I think once I get around to the new shocks, this is something that can be discussed with whoever makes them to achieve the clearance. With my 'discovery' of Delrin® I think the two parts I've made in nylon would be better if re-made in that material. We live and learn. Thanks to: - Fowlers Motorcycle Parts. 0117 977 0466