Checking Valve Clearances on your Motorcycle


One of our clients inline-four motorcycle has been given a basic clean bill of health. The only area that hasn't yet been attended to was the valve clearances.

If the gaps are too small we risk burning out valves, but if they are too slack the engine will sound noisy and performance may be compromised.

The last time the mechanic in charge of this motorcycle has adjusted four-cylinder valve clearances was some time ago, if I'm not mistaken it was a 1973 VW Beetle. As technology has unquestionably moved on since then I feel some on-the-job-learning might be the prudent and safest approach.

Lucky for the mechanic in charge several other mechanics seem happy to help, so it seem like an ideal opportunity to experience another masterclass in four-stroke technology.
In all honesty we're going to be looking to establish just how easy or difficult it is to measure valve clearance and what can be done if they need adjustment. Is this sort of work DIY viable or is it best left to the experts?

So is this a job for the home mechanic? In all honesty the answer is a qualified 'maybe'. If you are a competent enthusiast then yes it's perfectly viable. However, if you're a novice, unsure of what's going on or totally clueless it'd be quite easy to either get it wrong or give up half way through.

Treat each section of the job as a small project in itself and it'd probably be much easier and less challenging or daunting. If you needed the motorcycle to ride to work tomorrow we'd suggest you don't start working on it tonight straight after your evening meal. With sufficient time, the correct tools and some patience, checking the valve clearances should be within the capabilities of most owners who carry out some of their own maintenance.

As to adjusting the clearances should they be outside of the manufacturer's specifications; there are several levels of complexity, some specialist tools, some advanced mechanics and the odd potential disaster that need to be taken into consideration.

First to check the valves on some motorcycles you should remove the fuel tank and/or the airbox, on our motorcycle it's held captive on the frame with two lugs that push out of the frame side-spars. Each motorcycle is different so check before you start levering and pulling...

Often access is tight and the fuel injectors or carburetors need to come off. Taking the cables out at the twist grip is the easiest way to get some slack without overt disassemble.

When you finally removed the camshaft-cover retaining bolts loosened and a little tap with a rubber mallet the top-end is finally revealed. On our motorcycle the 16 cam-lobes and hollow cam-shafts look impressive.

The clearances are measured using feeler gauges with the highest point of the cam 180 degrees opposite to the valve/bucket. Due to the angle of our inline-four engine this obviously doesn't equate to vertical.

You could take off an engine cover and turn the crank over to move the cams. Or you could just think laterally and use a time-served method which is elegantly simple; a quick jerk of the rear wheel works beautifully. After you checked the valve clearances, putting it all back together is fairly straightforward, if time consuming. Camshaft box cover gaskets are available but often they can be cleaned and reused. A dab of the correct silicon RTV stops leaks at the stress points.
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