Shocking bearing breakdown
Experienced mechanic Richard Hewitt got a shock when a simple job turned bad
When a customer brought in his 2004 Kawasaki ZX636 for a rear tyre change, Richard Hewitt, a mobile bike mechanic working around Northampton, thought it would be a straightforward job.
“The bike had done about 25,000 miles and the guy had been riding a 90-mile round-trip commute on it. The first issue was getting the rear spindle out, I had to use a copper mallet, and then a wooden drift so I didn’t damage the threaded end,” said Richard.
“I lifted the sprocket carrier out of the wheel and that’s when the ball bearing fell apart! All the balls fell out and left the inner and outer bearing races in the carrier.” The races in a ball bearing are rings with a V-shaped groove which is where the balls normally sit. The large race that goes into a bore like the sprocket carrier is the outer race, while the small race on the wheel spindle is known as the inner race. The balls themselves are held in a cage, but that had completely disintegrated, allowing them to fall out. Richard explained: “I temporarily built the bearing back up which allowed me to remove both races together. Fortunately the carrier wasn’t damaged, so I was able to fit a new bearing and dust seal. It wouldn’t have managed another trip. In which case the wheel could have twisted out of line allowing the chain to jump off the sprocket, probably causing hundreds of pounds of damage as well as locking up the rear wheel and perhaps spitting the rider off.”
When Richard quizzed the owner he remembered it had been ‘a bit noisy’ for the last few weeks – a sure sign of trouble. This is why a weekly ‘walkround check’ is so important as it’s also possible to check for play at a standstill by getting hold of opposite sides of the tyre and rocking the rear wheel back and forth.
‘It would not have managed another trip’