Tronteck, as the valve rocker pounds up and down if the adjuster is not tight the thread starts to travel in the tighter direction (less clearance) on mercedes gas engines. Mercedes used to specify clearence checks every 10k if i remember. Ignore this and pull head to change the burnt sodium cooled exhaust valve before another ten K was travelled in many cases. At some point mercedes made the interference fit of the adjuster threads much tighter and they became a bear to adjust but lessened the problem enormously. The diesel uses a different set up of two nuts pressured together with two wrenches to lock the setting called a jamnut arrangement i believe. If not tight enough the adjuster thread starts travelling again decreasing the clearance even on that design I believe. One might be prone to think the clearence would loosen and increase but the reality is it moves towards reducing the required operating clearence.