Shock­ing bear­ing break­down

Ex­pe­ri­enced me­chanic Richard He­witt got a shock when a sim­ple job turned bad

MCN - - CONTENTS -

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’

The bear­ing fell apart as the cage had dis­in­te­grated

Ex­pe­ri­enced bike me­chanic Richard has seen it all

WHAT IT LOOKED LIKE

WHAT IT SHOULD LOOK LIKE

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