When mounting a timing belt (or timing chain
it is critical
to maintain the
correct orientation between the camshaft
and crankshaft sprockets
camshaft aligned 180° out of phase
will cause impressive backfires
possibly engine damage. A camshaft even a few degrees
out of correct position
will cause rough running and possibly engine damage.
Many (most) new timing belts come from the manufacturer with marks intended
to ensure correct alignment. In the event that the belt has no mark or a used
belt is being re-mounted and its marks have worn off it is advisable to make
temporary marks on the old (and new) belts to aid reassembly.
The camshaft and crankshaft sprockets will have one or more registration marks
to aid correct belt or chain mounting. Often but not always, these are intended
to be used with the crank at TDC.
The belt tooth which aligns with the mark on the sprocket can be marked using
chalk, other materials handy in some shops include lipstick or nail
polish. Nail polish being semi-permanent (and requiring time to dry) is better
suited to enhancing the visibility of the sprocket marks, which can be
helpful when working in poor lighting conditions.
Never fold a timing belt, and avoid forcing it into a radius smaller than
the smallest sprocket it passes over in use. Forcing it through too
small a bend can cause delamination or damage to the fiber construction, possibly
resulting in early failure.
Generally high performance engines sustain severe damage when a timing belt
fails, however most modern engines are designed such that there will be no
damage. As examples, a volvo 240 series just stops running when the belt breaks,
while a Ducati would usually suffer serious damage to head, valves and piston.