Prior to the start of this process, it is necessary to acquire two 6 x 1.0 mm bolts, 16 to 20 mm in length called service bolts. The procedures include positioning it at the top dead centre, thereby utilizing the respective tools to remove the valve covers, 
Timing Belt and the camshaft sprocket. You should use a dial indicator to achieve measurements on the camshaft thrust clearance; if the measurements are over the service limit, then you are indebted to replace the camshaft or the cylinder head. First, for each of the four camshafts, install plastic bushings around the exhaust camshaft subgear, then unbolt intake cam, and finally unbolt exhaust camshaft. Be sure the cam timing marks on the drive and driven gears are lined up, and aligned properly according to the right and left cylinder head. Fasten the exhaust camshaft sub-gear to the driven gear with a service bolt and then slacken the intake camshaft bearing cap bolts in a quarter turn at a time till they are ready to be removed, as the sequence suggested. To do this, unbolt the bearing caps and, very carefully, lift the intake camshaft up and level it. Repeat for the exhaust camshaft using the stored bearing caps in the correct order. In any case, it is possible to take out the valve lifters and shims together with the help of a magnetic tool, and keep them in different containers to prevent confusion. Remove an exhaust camshaft gear by firstly, gaining access to the cam, then engulfing it in a vise and finally using service bolts to take off the final sub gear. Check and indicate the thickness of the end gap of the camshaft gear spring and compare with the standard, if different then replace it. It is necessary to clean out the valve lifters, label and take off the shims, checking each lifter, its wear and the oil clearance. Checked for cam lobes and bearing journals for any signs of damages and measure the height of the each camshaft lobe and diameter of each journal replacing any that orginal specifications. Whenever the journals are excessively worn, use Plastigage to measure the oil clearance of each camshaft journal and change the camshaft or the cylinder head. Intially, bolt-in both the camshafts without the lifters or the exhaust camshaft sub gear, and measure the gear backlash with the help of dial indicator. Replace the camshaft gear spring, sub-gear, wave washer, and snap-ring into the exhaust camshaft gear so that they can be refitted back on the camshaft and the camshaft be mounted in a padded vise for proper fixing. Place one service bolt through the first unthreaded hole you saw of the camshaft subgear with the hole and tighten one other service bolt to join the gears tightly. Insert the valve adjustment shims and place the lifters in their original position; use moly-base grease or engine assembly lube on the lifters. It is preferable to use the camshaft installation lubricant to lubricate the exhaust camshaft lobes, bearing journals as well as the contacting face of the camshaft gear this is followed by positioning of the same exhaust camshaft in such a manner that its mark is aligned to the center of the head. Use RTV sealant on comer edges of the front bearing cap cylinder head mating surfaces, fit the bearing caps according to numbers and tighten the bolts to 1/4 turn each time. Replace the camshaft oil seal, oil the intake camshaft lobes and put the intake camshaft with timing mark facing the exhaust camshaft timing mark. Put the bearing caps in order and tighten the bolts, next undo the service bolt on the exhaust camshaft subgear, replace the camshaft sprockets and timing belt. Install the rest of the components in the reverse sequence, ensure to apply RTV sealant around the valve covers. Where the rubber half-circle plugs are situated at the back of the heads, clean this and put back with new RTV sealant. Last of all, commence the engine and look for any signs of leaks and other malfunctions.