Miata Mailing List: June 1994, Message #219
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   From: benagh@ICD.teradyne.com (Jeff Benagh )
Subject: Re: burned out exhaust valves
   Date: Fri, 10 Jun 1994 15:23:46 -0400

> * 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.

In my air cooled VW days, it came from poor adjustment of the exhaust valve in
the too-tight (clearance (lash) too small).  I believe these cars have hydraulic
lifters that don't require adjustment, and I don't know how to measure the 
specs.  Checking the specs is probably not a common practice in service for 
hydraulic lifters (in theory (and generally in practice) they are self-
adjusting), but should be for mechanical lifters.  Use of wrong kind of oil (I'm
not sure what "wrong" is though) could lead to lifters operating improperly.  
Excessive operation at high revs can also cause exhaust valve leak if the valves
are "floating" (not quite closing all the way before ignition).

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

see above.

jeff