PURPOSE: To easily assemble a timing driving mechanism for an engine by providing a pair of opposed circular grooves and a pair of guide channels for receiving a timing chain.

CONSTITUTION: A sprocket 14 is loosely received in a circular groove in a sprocket holding and chain guide member 21, a timing chain 15 is engaged with both sprockets 13, 14 and received in a channel defined by a flange and both walls 42, 42 and a sprocket 13 is received in a circular groove formed by a flange and a plate 34 fixed to an end flange with a screw 33. The sprockets 13, 14 are mounted at the ends of a crankshaft 11 and a cam shaft 12 and the member 21 is mounted and arranged in an engine block 10 with a bolt 16. The sprocket 13, 14 and the timing chain 15 are easily assembled as one unit in a timing relation on the engine block 10 together with the member 21.