Replacing timing belts or chains can be challenging to replace. Many of these look complicated to replace, especially on 16 valve variants. Many manuals recommend the use of timing lock kits. Most of the time these aren't needed for timing belt replacement. But are required when the belt has snapped causing internal engine damage.
Before you start it is paramount you establish if the engine has a floating crank pulley. Some ford petrol engines and Renault engines have these, so be aware. And can if not addressed cause catastrophic engine damage.
This is a guide and not vehicle specific so some variations may be found with different vehicles.
So to start. In most cases you will need to get to the timing belt or chain which means you will have to remove the air box, coolant header tank, and engine mount. Followed by the timing cover or casing. Removal of a road wheel, wheel arch liner and engine cover will be necessary.
This is now where the interesting part starts. You will need by my recommendation a brightly coloured marker pen. Then complete the following.
Mark the cam shaft pulley at the top clearly on the front face of toothed recess then along timing belt to the back plate. Also mark top of belt Top. This is a reference for yourself when replacing the new belt.
Mark all other toothed pulleys the same including the crank pulley, irrespective of it being floating or not.
If the engine has a floating crank you need to mark the flywheel the same. Some engines you may need to remove a flywheel cover. This gives you a reference mark when refitting new belt.
Now simply remove belt and replace all guides, adjustment pulley and water pump if leaking or has a worn bearing.
Take the old belt and place alongside the new belt, marking new belt exactly the same as the removed belt. This ensures once replaced all markings will be in exactly the same place from when it was removed. More importantly you will know it's fitted correctly and the timing will be perfect.
Now refit timing belt and tension observing recommended tension procedures. Some vehicles like Volkswagen Diesel engines are very difficult to fit the new belt. This is easily resolved. Prior to fitting belt leave bottom guide off until the new belt is fitted. Then simply fit the replacement pulley and tension.
Ensure all timing marking are correct. In the case of a floating crank pulley, refit pulley tightly. Then rotate engine two full crank shaft revolutions and check all timing marks match up. Only the pulley markings will marry up showing correct timing. All other markings need to be ignored.
Simply rebuild in reverse order and test drive.
This guide can be used and or interpreted for most vehicles and engine types.