T A C  Motoring

     The timing belt/chain is a critical component in engine which failure causing serious internal engine damage. Pistons are
still moving up and down when valves not.
The piston will hit a still open valve can bend
the valve, make a hole in the piston or even
brake camshaft or crankshaft. In many
cases engine after cambelt failure has to be
 replaced.
    Cambelt not giving You any warning that's
why should be replaced during time or
mileage intervals follow manufacturer
specification. Because cambelt has got internal inextensible twisted cords  is not possible to state visually its condition. That mean if you've car with unknown cambelt history you probably using your vehicle on your own risk to serious damage your engine. Together with cambelt are as well pulleys, tensioner most vehicles water pump. Those components very likely will warn You with specific sound which less experience driver can figure out.
    If your timing is driving by chain is less possible to fail this component without any sign. As well as cambelt has got replacement intervals. The difference between cambelt and chain is chain become noisy when is excessively wear, that's mean needs to be replaced. It's some little fracture of engines or specific cases when chain is failing in quiet, excluding wrong designe or weak parts, because oil change was overdue in the past.