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Eagledriver Eagledriver is offline
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Join Date: May 2003
Posts: 3,181
Brian,

Sorry to hear about your clearance difficulties. It seems that with "S" cams these clearances are very tight. I had to have my piston pockets cut deeper on my 2.7 for the same reason. For starters the clearances you see in Waynes book and on this web site are more conservative than Porsche used. This is for good reason as many of the engines we are dealing with are for racing or are made with aftermarket parts. Porsche only references the intake valve clearance on one page of it's workshop manual. It says the clearance should not be less than .8mm. There is no reference for the exhaust clearance. In Bruce Andersons book he recommends 1.5mm minimum. The exhaust is more critical because the piston is "chasing" the exhaust valve so any float at all or expansion of parts due to heat will reduce this clearance. Personally I would accept a minimum or 1mm on intake and 1.5mm on exhaust. If you can adjust the cam timing to achieve that you may be ok.

Other options are to have the pistons cut (many machine shops can do this), or putting a thicker base gasket on the cylinders.

Good luck on your project.

-Andy
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72 Carrera RS replica, Spec 911 racer
Old 08-29-2004, 11:28 AM
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