"Fredxx" wrote in message
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I am aware of a 1300 Ford Escort where after a prang had the throttle
jammed. It wouldn't restart. The valves had touched the pistons and bent.
No other damage and worked fine after the valves were replaced.

Hmm. They were lucky the valves didn't punch a hole through the pistons.

I remember my garage warning me with my first diesel car that it was an
"interference engine" - ie the valves occupied the same space as the top of
the piston, though at different points in the cycle. Consequently it was
even more important than normal for the timing belt to be changed at the
manufacturer's stated intervals, in case it snapped and the pistons and
valves collided. The garage also advised with my present car that they
should change the water pump (driven off the timing belt) while they were
replacing the belt, even if it seemed fine, so as to not incur a second
engine removal cost if the pump should subsequently fail. The extra cost of
a pump that may or may not need replacement was peanuts compared with the
labour of making the timing belt accessible - so kill two birds with one
stone.