In models prior to 1990 the timing gears are used while in models from 1991 on the hydraulic tensioner, timing chain and sprockets are used. The timing gears on 1990 and earlier models cannot be accessed or replaced while the car is intact, but those of the 1991 and later models can by means of their timing chain/sprockets. To reach the timing cover, one needs to first remove the crankshaft pulley, then to unbolt the timing gear cover with 6 bolts and clean the sealing faces with a scraper and a degreaser. If necessary, remove the front oil seal by gently wedging it out and fitting a new one with the sprung belly towards the inside, using a sealer inserting tool or a considerable socket and hammer. RTV sealant should be applied across the mating areas of the front cover and oil pan and then the cover should be placed over the dowel pins, the crankshaft pulley, and the cover should be fastened with bolts, and they all should be tightened in a diagonal manner in equal intervals. Last but not the least, fit the crankshaft pulley back again into its place. On 1991 and 1992 models the timing chain should be checked for wear, and it should be replaced if the engine has high mileages, if it shows signs of damage or if there is excessive movement. Where possible, look at the sprockets and look at the tensioner for the timing chain and replace also if damaged. To take out the timing chain and sprockets one should turn the camshaft bolt, then set the timing marks at Top Dead Centre, and then take out the camshaft sprocket bolt without rotating the camshaft. Remove the timing chain and sprocket assembly carefully and always replace the timing chain and sprocket as a set and the key should be in position. Wash the parts with some solvent then dry the components using a puff of compressed air while maintaining eye irritation. Reassembly is done in the reverse of disassembly, and every fastener has got to be tightened to the prescribed torque values and the chain and sprockets have got to be coated with clean engine oil before having the timing chain cover put back on.