1.7.1 Gear Train and Timing
DETROIT DIESEL 53
The camshaft and balance shaft gears on an In-line engine mesh with each other and run at the same speed as
the crankshaft gear. Since the camshaft gears must be in time with each other, and the two as a unit in time
with the crankshaft gear, timing marks have been stamped on the face of the gears to facilitate correct gear
The symbol system of marking the gears makes gear train timing a comparatively easy operation. When
assembling the engine, it is important to remember the engine rotation. Then, working from the crankshaft gear
to the idler gear and to the camshaft and/or balance shaft gear in that order, line up the appropriate circle
symbols on the gears or the appropriate triangles as each gear assembly is installed on the engine. Refer to
Fig . 1 for a typical gear train timing arrangement.
NOTE: It is advisable to make a sketch indicating the position of the
timing marks BEFORE removing or replacing any of the gears in the gear
The circle and the triangle are the basic timing symbols stamped on the gears. The letters stamped on the
crankshaft gears identify the proper timing marks for the particular engine: "I" represents "In-line" engine, "R"
represents right-hand rotation engine, and "A" represents advanced timing. Effective with engine serial
numbers 3D-64404, all Series 53 vehicle engines are built with advanced timing. The timing is advanced by
aligning the proper "A" timing mark on the crankshaft gear with the circle-triangle timing mark on the idler gear.
The camshaft and balance shaft gears are positioned so that the circle timing marks are adjacent to each other
(Fig. 1). One circle-triangle timing mark on the idler gear is aligned with the second "circle" on the mating
camshaft (or balance shaft) gear. The other timing mark on the idler gear is aligned with the proper timing
mark on the crankshaft gear. The crankshaft gear is stamped '"IR-A" on the left