In June 2006 I had the timing belt in my '95 replaced. I assume that they replaced the valve cover gasket as a result. About a year later the valve cove gasket started leaking from the rear; it was tightened and that seem to be all that was needed. In May 2009 I had the valve cover gasket replaced because it was leaking from both sides. Now,
12/2001 it is leaking once again and needs to be replaced.
Is it common for valve cover gaskets in a Miata to fail so often? Could there be something about the brand of the gasket (unknown) that was used by the mechanics. Could it be an indication of some other issue? If I do it myself this time are there any gotcha's to watch out for?
As always, I appreciate any advice I may receive about this.
Id order a new gasket, and if needed (Don't remember about 95's) the half moon plug. Anyway, it's fairly easy to screw up the gasket install. It's usually a rubber gasket, and does deteriorate with age. A thin coating of an RTV like gasket material should be used when installing a new gasket. The bolts should be tightened in the usual pattern, and gradually, do not over tighten. What usually happens when things leak is that the bolts were not tightened properly, or the gasket got "pinched". I have a 99, and am on the second gasket. About six years ago, I had the valve cover off to clean out the internal metal mesh filter. I reused the gasket, and it (Knock on wood) Hasn't leaked since. The original gasket was replaced some years previous to that after a valve clearance check.
The secret to reusing the gasket, assuming it's not damaged, is to clean everything up, and apply a thin coat of RTV like gasket goo, (from a fresh tube) place the gasket in the slot, add a thin coat of the same goo to the mating surface, assemble, then tighten the bolts in a balanced pattern so the valve cover gradually seats evenly. You actually partially torque the bolts during this process, wait a few minutes for the goo to ooze and gradually tighten to the final torque. Since the bolts are small, and they are going into aluminum, do not over torque. I don't have the manual handy, so I don't have the correct torque value at hand.
Too little goo and you get leaks. Too much, and it oozes into the inside of the valve cover as well as the outside.
Thank you Charlie for the detailed reply and Frank for the reality check. Guess I will replace it myself so I know it is done correctly. Have Rod's manual for reference on the correct tightening pattern. And I will get the OEM gasket instead of the aftermarket ones which may contribute to the problem. Thanks again.
One thing I forgot to mention -- A common source of leakage is at the rear half moon plug. There is an area at the top of each end of the half moon that has a tendency to leak. It also shrinks and gets hard with age. This might be where your leak is.
My 90 does not have the half moon plug, but there are some areas where a dab of RTV is required per the shop manual. Like previous posters, I do not have an issue with a leaky cam cover. After 244K miles it has seen a few timing belt changes and, always, a new gasket (with RTV blobs).
MotorsForum website is not affiliated with any of the manufacturers or service providers discussed here.
All logos and trade names are the property of their respective owners.