Valve/Cam-cover gaskets
Pre-empt - Watch for oil-seepage into spark-plug holes.
Every 6 months after 50k miles remove ignition leads & plugs,
cleaning both and to clean the spark-plug hole. Oil seepage that
does occur is very minor into a non-draining cavity.
Cam cover bolts can be retorqued, but must not be overtorqued.
Specification is a tiny 5.0-8.8Nm. Tightening procedure is start
at the top-left of each cover and work to the right until the end,
then back along the middle row to the left, then back along the
bottom row to the right. Then for each cover retighten the two
bolts between the three spark-plug wells.
The black valve/cam-cover gaskets themselves dry out and no longer
have the required elasticity to gap-fill - the gasket does the
sealing and not the torquing of the bolts. When the gaskets have
dried out through age & thermal cycling they need to be replaced.
Symptoms
Oil in spark plug wells, oil wet ignition leads, stuttering and
miss-firing. Middle spark-plug holes seem to be most susceptible since
they are central regarding heat source & limited cooling.
Solution
Replace gasket; front is 1 hour labour or DIYable, rear is 4 hours labour.
The rear requires removal of the aluminium intake and new intake gaskets
must be fitted to avoid an ECU undetected lean condition at a cylinder.
Gaskets are 20ukp/20$US from Mazda dealers. Silicone sealant dressing of the
gasket is required and at four obvious points (when gasket is removed) and
must not come into any contact with the camshafts or engine oil. Loose
silicone can starve parts of oil, from HLAs to camshaft bearing journals.
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