30-01-14, 12:15 AM
I change quite a lot of plugs in a year, nearly always Bosch or NGK, never had a problem, depending on what age your Focus is the mechanic could have damaged the plug lead when he was changing the plugs, coils do give problems to on that model. I think they have changed the plugs though as the car was on 4 when you put in and it is obviously not now.
If you worried about falling off your bike, you'd never get on.