One of the actions in the Tuner Engineering commissioning instructions was to recheck the tappet clearances once the engine had been run up to temperature. Clearance, sometimes known and valve lash, is measured between the top of the valve stem and the underside of the rocker arm. In the case of the 2.25 engines (petrol and diesel), this gap needs to be set at 0.10″ (0.25mm). It doesn’t matter if the engine is hot or cold.
It’s important to have the correct gap as it allows for 2 things… to compensate for the laws of thermal dynamics as the valve stem heats up and expands and to ensure the valve opens and closes to their fullest extent. If the gap is too large, the valve won’t be pushed open far enough. If its too small, the valve may not close fully.
There are 8 valves (2 per cylinder) that need to have their gaps set. To do this, the rule of 9 is employed.
- To set the gap on valve number 8, turn the engine until valve number 1 is fully open.
- To set the gap on valve number 7, turn the engine until valve number 2 is fully open. and so on…
Turning the engine can be easily achieved using the starter handle. Much more convenient than a spanner on the end of the crank.
First thing to do is remove the air cleaner assembly, rocker cover and the 4 spark plugs. With the spark plugs removed, turning the engine is a lot easier as you’re not fighting against compression in the cylinder.
I noticed that the spark plugs were quite coked up, so they had a quick clean up whilst they were out of the cylinder head. Coking is caused by the fuel / air mixture being too too rich. An excess of fuel in the mixture will cause coking as not all of the fuel is burnt during combustion and forms a sooty deposit on the electrode. Having spent some time fettling with the timing / mixture in recent weeks, I’m not that surprised to find this.