Question 1

When valves need adjusting

Accepted Answer

Valve clearance can drift over time — either opening up (ticking) or closing up (valve doesn't seat properly, so compression drops). On older engines with mechanical tappets and lifters, adjustment is part of the manufacturer's service schedule. The interval is typically 60 000–120 000 km depending on make.

Typical symptoms that adjustment is due: a metallic ticking from the rocker cover (especially when cold), power loss, rising fuel consumption and rough idle. An engine warning may come on if valve timing has shifted significantly. Further neglect can lead to a burnt valve, which is a much more expensive repair.

Question 2

How valves are adjusted

Accepted Answer

The rocker cover is removed and the camshaft position is marked. Each valve is checked with a feeler gauge at the manufacturer-specified clearance (typically 0.20 mm intake, 0.30 mm exhaust). The crankshaft is turned by hand so that each valve in turn has its cam base upwards — with that position the clearance can be measured.

Adjustment is either by screws (common before the 2000s) or by shims (common since). In a shim system each valve gets its own thickness of shim, selected from a kit based on measured clearance. After adjustment the rocker cover is refitted with a new gasket and the engine is started — the ticking is gone and the engine runs smoothly.

Question 3

Why does valve clearance change?

Accepted Answer

Valve stems and lifter contact surfaces wear over time, changing the clearance. Exhaust-side valves typically wear more than intake because they face higher temperatures and more chemical stress. Valve seats can also wear and the valve starts to "sink" into the cylinder head, reducing clearance. If clearance becomes too small, the valve doesn't close properly, combustion chamber compression drops and the valve burns quickly. Regular adjustment per the manufacturer's schedule is therefore important.

Valve Adjustment in Vantaa