Miata Mailing List: June 1994, Message #217
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   From: "Christopher Buja" 
Subject: burned out exhaust valves
   Date: Fri, 10 Jun 1994 15:05:56 -0400

                      burned out exhaust valves
have just encountered engine troubles with a '90 Miata at 64K miles.    I have
five questions 

* Background *
service following a failed emissions test identified a cylinder with low
compression.  Opening the engine, the dealership shop reported back that the #2
cylinder's exhaust valve was shot and the others were not much better.   This
is consistant with symptoms, so I think that they're on the  mark with the
diagnosis -- my questions focus on the cause

* Question 1 * 
Does anyone else see this problem?  64K miles seems *very* early for engine
breakdown.  Dealership shop tried to indicate that this was not abnormal for a
Miata. 

* Question 2 *
What causes the exhaust valve to get burned out?   My understanding is that
when it's not due to a defective valve, it comes from running too lean -- or
having the timing out of adjustment.

* Question 3 *
Is it a question of maintenance?  The dealership has done all the service at or
before the suggested intervals.   

* Question 4 *
Why hasn't the problem been detected?  The car had just been in for the major
60K service just nothing surfaced until I went for the Smog Check.  The station
went on to point out that if the problems been active for a long time, then the
catalytic converter might be affected.  That's when I hit the roof, letting
them know that If they've missed the problem for a long time, then they needed
to share the responsibility

* Question 5 *
Any suggestions on what tack do I take with the shop?