In article <jason-1405051024490001@pm4-broad-50.snlo.dialup.fix.net>,
jason@nospam.com (Jason) wrote:

> > Ask him what happens if the timing chain breaks. Does the engine trash
> > itself, or not? I think Toyota's are the non-interference type which
> > don't trash themselves. At any rate, that's the important question. It
> > doesn't matter if it's a belt or a chain. There's still chance for
> > breaking, and there's still a requirement to change (although a chain
> > *should* go much farther in theory).
>
> Great post. It's my opinion that a broken timing belt would in most cases
> do less damage to an engine than a broken chain.

That depends on whether the engine is an interference design or a
non-interference design.

It's not just the physical belt or chain whipping around in there; it's
the pistons and valves you have to worry about.

With Honda, the valves go down inside the combustion chamber. If the
timing belt or chain breaks, the valves stay down there when the piston
comes back up to top--and all hell breaks loose when they meet. That's
called "interference".

If the engine is designed, however, such that the valves don't go down
inside the combustion chamber, but rather stay outside the combustion
chamber, it doesn't matter what happens when the belt or chain breaks.
The engine quits running, but a simple belt/chain replacement fixes the
problem. No trashed engine to worry about.

As far as the earlier comment regarding timing chains stretching, that
happened to my brother's 92 Infiniti Q45. He had to replace both timing
chains, at some unholy cost ($2700 comes to mind). It wasn't that they
broke, but rather that they had stretched far enough out of spec.