The good weather means we are all putting more miles on our cars and one thing always worth checking is the tension of your fan belt.
 
The SC fan belt uses a very simple system made of two separate pulley halves and six shims to set up the belt tension and this allows for easy preventive maintenance (a broken belt could lead to potentially catastrophic consequences).
 
You should always use the six shims and if you are replacing the belt, a good starting point is to put five shims inside the outer pulley and one outside.


 
If you are only adjusting the tension and not replacing the belt, put more inside the pulley to slacken the belt, and less inside to tighten. 
 
Most important is to make sure that are all used. 
 
Be careful not to crush/distort any when fitting them and a good trick is to put a smear of grease on the shims on the outside so they stick to each other (they can be tricky to keep in place). 
 
Another trick is not to use the special pulley holder at first. 
 
Just tighten the nut, turning the engine (which turns the pulley), checking the shims have not fallen to one side. Then, when you get to the point that all you are doing is turning the engine with your spanner, put the special pulley holder on and finish tightening the belt.Give the nut a final torque of 40Nm (29.5ft lb) and if not using a torque wrench, just tighten as hard as you can with the pulley wrench from the factory tool kit, you should not be too far off.
 


You can then do a final check of your belt tension and fire your engine, looking at the belt while revving the engine to see if the belt is no longer loose. 
 
Fire up the engine and let it run for a couple of minutes, so that the belt adjusts into its correct position. Shut down the engine,  place a couple of fingers on the belt halfway betwen the pulleys and push gently to deflect the belt. Correct tension is achieved when the belts deflects ¼ to ½ inches. 
 


While adjusting the belt tension, always move only one shim at a time and test, making sure you fully torque the nut before firing up the engine.
 
Keep in mind that new belts do strectch a little at first, so re-check the tension after the first drive and adjust if needed. And remember, it is always worth keeping a spare belt one in your car just in case of a failure half way through a long journey away from home.