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304065 304065 is offline
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Join Date: Dec 2001
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Now, turning to the piston itself, these are the dimensions:

The bore threads are M18 x 1.5, same as an oxygen sensor.

Now, look carefully at the top of the piston and the bore from the endoscopic photos. See how the piston has a chamfer? In hydraulics, this is called a "pop-action" design-- you can see that a much smaller surface area is exposed to oil pressure when the piston is seated. As soon as the pressure on that smaller area becomes sufficient to lift the piston off its seat, then the full piston area is exposed to oil pressure, which "pops" the valve open immediately. This is a desirable property of pressure relief valves and the factory was smart to include that feature here.
'66 911 #304065 Irischgruen
'81 R65
Ex-'71 911 PCA C-Stock Club Racer #806 (Sold 5/15/13)
Ex-'88 Carrera (Sold 3/29/02)
Ex-'91 Carrera 2 Cabriolet (Sold 8/20/04)
Ex-'89 944 Turbo S (Sold 8/21/20)

Last edited by 304065; 10-22-2012 at 11:44 AM..
Old 10-22-2012, 11:42 AM
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