911/Carrera Q&A

  
     
Question: I have a '79 911SC, in my Clymer repair manual, the valve overlap is shown to be 0.039". My reading is 0.055", should I be alarmed at this discrepancy?  
     
Answer: I've never seen the spec in inches, but I will do some conversions to make it easy. The factory spec for your car is 0.9-1.1 mm (.003-.043") and the ideal setting would be 1.0mm (.039). What you have - .055" (1.39mm) is off but still very close to the spec for a Euro SC (1.4-1.7mm, .055-.066") or an '80 and later US model SC (1.4-1.7mm). I would not be worried, someone may have set the car to the wrong spec, or, from chain stretch this could be where the car in running. If you are re-timing the cams just set them to 1.0mm (.039") and you are ready to go. The conversion is mm - inches x .03937 and from inch - mm x 25.4.