Timing Components: Description and Operation

NOTE: Only the latest chain tensioner is carried as a spare part, the earlier one having been discontinued.





The timing gear comprises sprockets and a chain, together with one fixed and one pivoting chain guide. Chain tension is maintained by the pivoting guide and a chain tensioner.





The camshaft sprockets have 38 teeth and are secured by means of a centre-bolt. They are located on their respective shafts by means of a slot on the sprocket and a corresponding dog on the shaft.
The crankshaft sprocket incorporates a keyway to locate it on the crankshaft. It has 19 teeth and is secured by the centre-nut for the crankshaft pulley.
The chain is an endless single chain of 126 links, with rollers having a diameter of 6.35 mm (0.25 in).





The fixed chain guide is made of rubber-clad steel and incorporates a groove for the chain. It is held in place by two bolts. The pivoting chain guide is made of light-metal alloy coated with rubber and also incorporates a groove for the chain. The guide is pivoted at the bottom.





The chain tensioner is hydraulic and incorporates a spring and ratchet. It is fitted in the cylinder head and acts on the pivoting chain guide.





Chain tensioner, M88 onwards. The latest chain tensioner has a tighter adjustment range than the earlier version, thus providing both more-precise compensation for chain wear and quieter operation.The function is both mechanical and hydraulic, the tensioning force being provided by a spring acting on the tensioning arm. A ratchet prevents return of the tensioning arm inside the tensioner unit.