The first in an occasional series of items retelling events down the workshop.
After ten years we thought we’d seen everything and while most of the work is mundane, once in a while something comes up worthy of mention. Last Saturday was a case in point. One of our recent regulars came down complaining that his chain was making a lot of noise and had such a tight spot it was impossible to adjust. He asked us to order a chain and sprocket set (we don’t stock spares but we can order for guys we know). As we would be closed the next weekend (Bank Holiday) I suggested we take a look and see if there was anything we could do to relieve the symptoms (take two aspirin and ring me in the morning?). The bike was (is) a CBR600 which the guy bought last year with an unknown history. It’s a bit tatty and we noticed the sump plug had been drilled for wire-lock. The chain was well lubed and there were no stiff links. The profile of the rear sprocket was fine, hardly worn at all, with no signs of hooking. The cush drive had no play. There was excessive wear on the inside surface of the sprocket (side facing the wheel). When the wheel was turned the sprocket teeth caught the inside of the chain as they engaged. The problem was obvious, the rear wheel was mis-aligned, wasn’t it. Err No, it was fine. However, the slight gap between the sprocket carrier and the wheel was larger (1mm) at the back than the front, due to the carrier being pulled at a slight angle. A worn carrier bearing? It took a (very) large copper mallet and a air-hammer gun to remove the spindle which was covered in rust(?). The sprocket bearing had indeed failed but the design, including a stepped spacer, prevented much movement. The hydraulic press was reading over 8 tons as we removed the spacer from the bearing, even after soaking in plus-gas. An overnight soak and a blow-lamp may have reduced the force needed. The bearing was knackered (a British technical term) and since the wheel bearings also felt notchy, it was decided to replace all three as a set. The bearings were all shielded (both sides) which is not standard and among the numbers we were looking for were the words Made in England so these were obviously replacements. When the first wheel bearing was removed we got our next surprise. The wheel was full of rusty water, half a gallon! This wheel design has no air vents. Water must have been forced in with a pressure washer and trapped. The surface of the bearing spacer looked like an ancient cannon dredged from the sea bed. The assembly was put back together; twice. The second time to include that carrier bearing spacer! 'Dave, is this bit important?'... 'Oh f***'. Though the chain and sprockets could still do with renewing, the side wear causing excess clearance, the transmission was transformed. This story is a good example of a minor symptom being an indicator of a much more significant problem. The missing element in the previous maintenance of this machine being some TLC. If we don’t have anything of interest come up in the next few weeks, I’ll tell you all about the SilverWing rear linkage held up by 2mm of worn steel. Read next story Return to home page