Re: One valve down. Is it safe to drive ? (for a while ...).

[steveb@newkla.kla.com (Steven Buchholz)]

There has been a lot of talk on this one, but I haven't seen anyone address 
the original question ... should you drive a car if you know that a valve is 
bent?  Personally, I would say NO! ... but what more could happen?  The bent 
valve stem could ream the valve guide ... But would you replace the valve 
guide on a bent valve case as a matter of course?  The valve will be hit-
ting the seat funny and could damage it.  You don't know if it is an intake 
or exhaust valve, and you are doing nothing to prevent ignition of the mix-
ture in the cylinder.  If it were an intake valve couldn't you have the 
exhaust gasses fed into the intake manifold?  I know that some turbos have 
sodium-filled exhaust valves ... BOY would that be exciting if you just 
happened to crack one of them open in a running engine!  Was the piston 
damaged when the valve hit it?  (This could happen if the engine was running 
at higher revs when the belt broke.)  No, I would not drive a car knowing 
that it has a bent valve stem!

The other issue is ... is it possible that no valve stems were bent?  As 
I recall the car is a 5K turbo.  I believe the 5KT motor has the same 
piston design as the TQCoupe.  I know for a fact that the valves will 
contact the pistons if the cam isn't turning while the crank is.  The 
pistons are not relieved where the valves would meet them.  I'll bet 
that something touched something else.  

All of the above is my opinion based on my understanding of internal
combustion engines and Audis.  Am I overreacting?  Is it a case where 
simply unplugging the spark plug on the offending cylinder would allow 
use of the car at reduced capacity?  

Steve Buchholz
s_buchholz@kla.com

'88 5000CSQ Wagon
'83 TQCoupe (yes ... I've pulled the head off of this one!)
'78 Fox GTI