Valve clearances are important, but having them done by your dealer can be very expensive; it is one of the main reasons many motorcycles are traded. But ignore them at your own risk, as your engine can be seriously damaged over time.
Before buying my 1999 Kawasaki ZX-6R, I never checked the clearance on anything that didn’t have a bolt and locknut, but now I’ve realized how simple it can be …
That little metal disc looks so insignificant, but it’s vital to maintaining a healthy engine
What is valve clearances?
Valve clearances in motorcycle and automobile engines are effectively related to the gap between the top of the valve stem and the cam that operates it.
The engine inlet valves open to allow air and fuel to enter the cylinder, while the exhaust valves let out burnt gases. Needless to say, it gets hot inside the engine, so when the valves close, they close into a hardened ‘seat’, which acts as a heat sink. If the valves are not fully closed at the point of ignition and the expansion of the combustion gases pushing the piston downward, the valves will be damaged and the high pressure gases can cause serious and irreparable damage to the valves, seats and other parts inside the engine.
Why is it important to have a gap in the valve clearances? motorcycle clearances
If the valve clearance was set to zero, the valve could theoretically be set to close completely, but as the engine warms up, the parts expand; without space, the valve would not close completely. That is why valve clearances MUST be checked with cold engine stone.
How do I know when to adjust my valve clearances?
An incorrect valve lash will cause a malfunction and eventually serious damage to your motorcycle. You will find many forum and Facebook posts from people claiming that they didn’t bother and that their bikes are fine, but the damage will be progressive.
My ZX-6R hadn’t endured a difficult life, but at just over 18,000 miles, the exhaust valves were very tight. Personally, I would always look for evidence that authorizations were properly processed on time when purchasing a used motorcycle; it is a sign of a loving owner and will give you more confidence that the engine will last.
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What parts do I need? Self-adjusting and eliminates the gap between the camshaft and valve.
If you are lucky, when you have checked the valve clearances, you will find that they do not need to be adjusted. The exhaust valves are more likely to be off, but there is some tolerance; on my ZX-6R G2, for example, the inlet valves should have a gap between 0.11 and 0.19mm, while the exhaust valves should be between 0.22 and 0.31mm.
However, it is likely that at least one of the gaps will need to be adjusted. We are focusing on bucket and shim clearances here as it is the most common on modern motorcycles so you will need to purchase some shims. The problem is, you won’t know which ones until you’ve measured them, so expect to have your bike off-road for a few days, unless your local dealer has them in stock.
I got mine from Wemoto, where for this bike they cost between £ 2.20 and £ 4.85 each; if you buy them from Kawasaki, they would cost £ 9.50 each.
You will probably need some gaskets too – the pickup coil cover needs to be removed on my ZX-6R to set the crank position; A replacement gasket from Wemoto costs £ 3.42 and is the genuine Kawasaki part.
The Haynes manual says that the four o-rings that seal the camshaft bracket against the cylinder head should be replaced; As the oil was seeping into the plug wells, I changed them at a cost of £ 1.75 each, along with the four gasket bearing caps found on top of the camshaft bracket to £ 5.17 each. The cam chain tensioner O-ring should also be replaced at £ 1.86. This bike had been stationary for almost ten years, so it’s no surprise that some of the seals were failing.
If any shims need to be replaced, you’ll need some new motor oil to lubricate them, but you’re probably doing a full service anyway so keep it on hand.
What tools do I need? valve clearance
This article does not pretend to be all …