Thread: Kissed pistons
View Single Post
2.7RACER 2.7RACER is offline
Registered User
Join Date: Jun 2004
Location: Rio Rancho, New Mexico
Posts: 1,326
The marks on the pistons are telling us the exhaust valves tapped the pistons. If the cams were set at 1.4mm the exhaust valves would have been closed and the intake valves open. I'm going by the specs in Bruce Andersons "Porsche 911 Performance Handbook", pages 110 & 111. Please notice if the cams were set up to '76-'77 Carrera specs, 0.9mm to 1.1mm the exhaust valves would be open slightly more than the intake valves at cross-over. That is the exhaust closes at 3 degrees after TDC while the intake opens at 1 degree before TDC. From this info it looks to me as if your cams were retarded upon initial set-up. That is they were set LESS than 0.9mm. Anything over 1.1mm and the intakes would have been open more than the exhausts, and the marks would be on the intake side of the pistons. Timed at 1.4mm the exhaust valves close 3 degrees before TDC and the intakes have opened at 7 degrees before TDC. Since both sides were marked the same indicates both cams were retarded. It is unlikely both cams jumped at the same time. That's my 2 cents. Good Luck.
'76 911S 2.7, webers, solex cams, JE pistons, '74 exhaust, 23 & 28 torsion bars, 930 calipers & rotors, Hoosiers on 8's & 9's.
'85 911 Carrera, stock, just painted, Orient Red
Old 03-28-2005, 11:15 PM
  Pelican Parts Catalog | Tech Articles | Promos & Specials    Reply With Quote #21 (permalink)