‘I was expecting topend carnage, but he was a very lucky boy!’
Seasoned spannerman Neil Sawbridge says this Derbi owner had a lucky escape
hen this Derbi Cross City 125 rolled up onto Doncaster Motorcycles’ forecourt a month ago, you could hear a topend rattle ten yards away. Experienced mechanic Neil Sawbridge whipped the cam cover off to check the valve clearances and looked for any rocker wear, but everything was within limits, so it needed more investigation. “When the lad came back, he asked if it was ‘safe’? Which is such
Wa ‘how-long-is-a-piece-of-string’ question, especially with an Italian or Spanish bike. Hondas maybe, but you can’t treat a small-capacity European bike like a CBR600. But he convinced himself it would be OK for a while and rode away on it,” added Neil. One month later and the bike is back in a van after it cut out and wouldn’t restart. The camchain tensioner had failed and allowed the camchain to jump off a sprocket, so Neil got that sinking feeling when he looked at the timing marks on the cam sprocket.
“Although they were only a tooth or two out of alignment that meant the timing is actually 90 degrees out, so I was expecting top-end carnage with bent valves and a mashed piston crown.
“But he was a very lucky boy because the chain had jumped off the crank sprocket instead. It had jammed the crankshaft and broken a bit of the engine casing, but the engine had stopped dead because the timing cut out, so the top-end was undamaged.
“If it had jumped off the cam sprocket the engine would have rolled on and he would have been looking at a £400 bill. Instead he got away with £91 including parts and labour. But he had to wait six weeks for the parts so maybe he’s learnt a lesson.”
‘You can’t treat a small-capacity European bike like a Honda CBR600’