valve guides or what?
 

recently I noticed my 87 911 started to smoke. I thought it was strange (only 70k
mi) on car. It smoked just on starting , but the other day I noticed it smoking while idling in traffic (I had been driving over 2 hrs). I told my mechanic while he was performing 15k svc to look into it -he said there was oil on #6 spark plug and that it would be expensive to get into it. Any ideas on what it is and what it will cost me?

Of course it's hard to know the cause but very likely valve guides are worn. If you read books and answers to questions like this in Excellence from Bruce Anderson he says the oil consumption will increase above the factory limit (I think it's something like 1.5 quarts per 500 miles) and then the plugs will start to foul. Do you know what your oil consumption is? If your guides get to this point you must replace them or risk exhaust valve failure. I spent about 3000 dollars to do a top end with me doing everything but the machine work. I did some extra things to my engine though. The basic machine work on the heads is around 900-1100 dollars.

I would get a leak down test done. It should help you verify that the problem is in #6 and also alert you to where the problem is. I have doubts that a Carrera has valve guide problems at 70K... this isn't a smogged thermal reactor 2.7L. Burned valve?... broken ring? The leak down should be helpful.

a leakdown will not pick up a worn guide, just the results of the worn guide on the valve and seat. the valve wobbles around and basically beats the crap out of the seat. i've done valve grinds on carreras at 60K for fouling plugs. most make it longer, but not all. a complete VG with all new valves, guides, gaskets, tuneup parts, oil, filters will average $3200 in the seattle area, and they can certainly be more elsewhere.