Valves - solution and identification - Jonathan
Further to my last post.....

I have changed the spark plugs, to slightly hotter ones, still NGK though.
This will hopefully stop the misfiring which I now suspect was causing the juddering.

It also revealed that in 1 of the back 3 cylinders some oil was leaking into the plug and cylinder area. This was probably a fundamental cause of the mis.

So, next question.

It is likely that this will require some attention. After speaking to my friendly mechanic, it looks as though it could be either a replacement rocker cover or a cylinder head gasket. Are there any alternatives to this walletectomy?

Lets pray that the new plugs solve this issue.


Re: Valves - solution and identification - Michael
Jonathan, how do you know oil was leaking into one cylinder? was it because of the colour of the plug? Not always a reliable indicator. If that pot was misfiring for another reason, the plug may look an unusual colour. Have you had this engine checked by an engine analyser yet? May save money in the long run.
Re: Valves - solution and identification - Guy Lacey
Highly likely that the bad plug caused the black plug and NOT a poor rocker cover (!) or head gasket. A rocker cover failure will not give a black plug and a head gasket failure will be highlighted by high temp, water use, steam from zorst, etc and not a black plug.

Methinks black plug a symptom not the cause.
Rocker gasket leak onto plugs. - David Woollard
I think you guys may be misunderstanding Jonathan (or I am).

He may be saying there is an external leak of oil from the rocker/cam cover gasket to the spark plus well.

This and the dirt that accumulates can give a short to earth from the plug lead causing a misfire and black plug.

I have seen this specifically with the Renault Megane 1.6. There is a known problem with the cam cover gasket, Renaults have modded it now, and it gives just the symptoms described when it leaks..

Rocker gasket leak onto plugs - David Lacey
DJW - I thought the same too but I was just interested to see where the thread would go..........

Re: Rocker gasket leak onto plugs - Jonathan
The reason we suspect that oil is getting to the plug is that when we channged it, it was dripping with oil. The plug itself wasnt any more black than the others.

I should probably take it to Mazda and get them to plug into their diagnistic comp.

I have also tried STP complete engine cleaner (i think thats what it is called). This should also help to clean the valves etc, which may improve the problem.#


Value my car