Slack clearances between the rockers and valve stems can mean the valves open too late and may not open fully. That worsens performance and fuel consumption, make a clattering noise at the top of the engine, and can even fracture tappets and guides inside the cylinder block.
If clearances are too tight, valve will open too soon and close too late, again effecting performance and over heating sealing faces. The principals are the same for any engine with rockers even that side valve engines of the series 1 and the series 3 2.6 liter. Check pre Tdi engines every 6000 miles, Tdi every 12000.
Take care with feeler gauges, forcing them in a tight gap will score them. Aim for the feeler to enter with an easy fit that doesn’t allow any rock in the rocker arm (gripe the adjuster’s arm and lift it up and down to feel for movement). Afterward, wipe the feelers clean and smear lightly in oil to prevent rusting (which would make theme thicker, thus inaccurate). When using the rule of 9 to position the valve for measurement, turn the engine while watching a rocker push its valve down, compressing the spring, when the rocker stops moving down, nudge the engine a fraction more to confirm the rocker stays in position before adjusting the appropriate valve. If the rocker begins moving up, you’ve gone too far. Turn the engine again to restart the process.
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