Oren wrote:
On Tue, 8 Dec 2009 12:04:40 -0800 (PST), Larry Fishel
wrote:

On Dec 8, 2:42 pm, "JoeSpareBedroom"
wrote:
OK - so now that we've established that there's a broken spark plug
(assuming the mechanic's telling the truth), what are the various levels of
horror which could result from further diagnosis?
Worst case is something like:

The timing belt/chain is worn and skipped a tooth (just fixing this
could be a few hundred).
This caused the pistons to hit the valves, damaging the valves, a
spark plug, head, pistons and possibly even rods.
Broken bits of valve and/or spark plug gouged the cylinder walls.


How would slipped timing cause the piston to hit anything? Never heard
of such a thing.

Just consider basic mechanical engine timing. If the engine is an
interference design (common on many higher performance and import
vehicles) the pistons can definitely collide with the valves if basic
mechanical timing is lost (eg, timing belt stretches and jumps a tooth).