The Importance of Checking Valve Clearance

andrew Maintenance, Tutorials, Video 2 Comments

Suck Squeeze Bang Blow

The inlet valves and exhaust valves at the top of the cylinder allow fresh air/fuel in and burnt exhaust gases out, so that the four stroke (suck, squeeze, bang, blow) cycle can start again.

The four stroke cycle works most effectively by opening and closing valves at the appropriate timing with the rising piston and sparking plug. If the timing between the valves and the rising and falling piston is out even by a little (fractions of a second), the engine will not pump as effectively as it could, and therefore its output is compromised. I would encourage every motorcycle owner to take some time to check their own valve clearances. With a bit of spannering experience, it isn’t really difficult, but it does take some time and a few choice tools, and your bike might be out of action for a while. (Click here to see how its done on a Honda V-4 engine)

It’s a good job to do if you don’t ride in the winter, and your bike is sitting idle in the garage hooked up to its trickle charger. Time equals money when it comes to workshop bills, but with a few rudimentary tools and some time in the garage instead of in front of the TV, you can check and adjust valves yourself and save yourself a pretty penny. If you are unlucky enough to want to know more about the subject of valve clearance adjustment, have a trawl on the internet and you will find more bravado and bullshit on the subject than just about any other in motorcycle mechanics.

Some are adamant that manufacturers’ service scheduled are sacrosanct, others would swear that they never adjust their valve clearances in their bikes’ entire lives. Somewhere in the middle of that bell curve between morons and saints lies the rest of us; opinions and advice based upon empirical data on different bikes, manufacturers information, riding styles, and technical experience.

‘Advice’ to solve a poor running engine issues involves things such as sawing into airboxes, blocking off pipes and hoses and cutting wires in the fuel management system, issues that would likely be solved by a simple valve clearance adjustment. It’s funny that a valve clearance check is seen as the last resort rather than an integral part of your engine’s health check. These “experts” believe that their back alley ‘modifications’ might somehow improve their machine’s performance more so than automotive manufacturers’ multi-million pound R&D budgets and years of experience. But I digress…..

So should you stick to your 16,000 mile valve clearance check? What will happen if you don’t, and why is it so expensive to have them checked?