Miata Mailing List: June 1994, Message #221
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   From: mikef@mer-mail.ctron.com (Michael Friedman)
Subject: Re: burned out exhaust valves
   Date: Fri, 10 Jun 1994 15:55:16 -0400


 > Christopher Buja asks:
 > * 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.
 > 
 Exhaust valves burn out from excessive heat.  Usually because the 
valve lash is set wrong and the heat is not fully dissapated from
the valve to the head (lash gap too small).  If the Miata uses
hydrolic lifters (I think it does?) there should not be any way
for this to happen (except perhaps if the lifter is seized).

Other possibilities include detonation or pinging or preignition from
too low octane gas (or too far advanced timing).  Again - in a modern 
fuel injected car, the anti-
knock computer usually eliminates this, but if you burn regular 87 octane
gas, and perhaps your timing is a little too far advanced, a burned 
valve could result.

These are general items.  I've only had my Miata for 23 hours (about
200 miles - not bad for a work week - all top down!) and havn't 
purchased a shop manual for it yet, so I can not be specific.  

Hope this help...

Mike Fridman