Valves – why should you worry about ‘em…? Well, if you own a bike less than five or so years old you can bother a little less, because materials are so much better, tougher now than they were even just a short time ago (which is why service intervals have generally grown) but bikes like this 2005 Kawasaki ZX-12R really need regular valve clearance checks.
The reason is that over time the valve clearances have a tendency to close up; you’ll start to notice a slight loss of performance because when the engine’s hot the valve isn’t getting contact with the valve seat, therefore it can’t dissipate heat, and the valve and seat starts to burn out. In severe cases – which we’ve seen with some Kawasakis, mostly with race use – the valve can stretch enough to reduce the clearance enough so that it touches the piston, with disastrous results.
In short, if you own a pre 2004 or 2005 bike pay close attention to the valve clearance schedule – the new owner of this Kwak’ was lucky as its previous owners had adhered to the service schedule as witnessed by the rocker box cover, which had been stamped up inside with each check, just as we do. All of its clearances were within tolerance, but at least he had peace of mind of knowing that before he started piling on the miles.