Pistons hitting valves

[quk@sievers.com (Phil Payne)]

In message <3.0.1.32.19970618135524.006a358c@mail.swva.net> Brendan writes:

> I've heard and read about the concern of pistons hitting the valves when
> the timing belt breaks (or when changing the belt, I suppose).  I was told
> by a mechanic that the engine (or perhaps it's in the design of the heads?)
> in my '87 5ksq was designed such that this was not a concern because the
> valves didn't drop down far enough or the pistons rise high enough for them
> to clash.  Can anyone confirm this, or is anyone aware of which (if any)
> Audi engines were designed this way?

Your engine is a non-interference type.  In theory, nothing bad can happen if 
the timing belt breaks.
 
However - many of us suspect that a worn engine may (via crank journal, big and 
little end wear) _become_ an interference engine in later life.  There's also 
the issue of speed - an engine that can be turned by hand without interfering 
might well interfere if the parts are being flung about at 6500 rpm.
 
So the only _safe_ approach is to treat all Audi engines as interference 
types.  Your mechanic's theory is correct - but none of the regulars here would 
rely on it.

--
 Phil Payne
 phil@sievers.com
 Committee Member, UK Audi [ur-]quattro Owners Club