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Join Date: Jan 2005
Location: cooperstown NY
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too much valve clearance?
during my stock 72 2.4 E rebuild:
deck clearance 1.5mm set cam timing as per specs. the CLOSEST my valves came to the piston was 5 mm. i know too close (intake 1.5mm, exhaust 2mm) is bad, but can you have too much clearance? does 5mm sound reasonable for a stock E cam with stock E pistons?
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bob 1972 E pos correction: expensive pos someday.... "shut up and drive!" |
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03-20-2010, 04:49 PM
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3 restos WIP = psycho
Join Date: Feb 2005
Location: North of Exit 17
Posts: 7,665
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No clue, but as long as your deck height is right, your valves are adjusted right and your heads cc out OK, I don't see why it is an issue. The E cam is not high lift and the E was designed with lower compression in mind, so those domes aren't going to rise very high into the chamber.
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- 1965 911 - 1969 911S - 1980 911SC Targa - 1979 930 |
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03-23-2010, 04:01 PM
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thanks kenik.
i'm suffering from rebuild paranoia. as the $$$ goes up so does my anxiety!
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bob 1972 E pos correction: expensive pos someday.... "shut up and drive!" |
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03-23-2010, 04:08 PM
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I have two points about this. The first is that your deck height is kind of high. This engine is a low compression engine so I would run it at 1mm deck height to maximize your compression. The second point is about your valve to piston clearance. Are you measuring at TDC? If so you are not measuring the closest clearance. This is a common misconception. Closest clearance for the exhaust valve is before TDC and for the intake valve is after TDC. How much before and after depends on the engine. I'd measure at 5 degrees and 10 degrees.
With the 5mm number you found, I wouldn't bother measuring at the other numbers. You have plenty of clearance. -Andy
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03-27-2010, 07:41 PM
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At TDC the clearance is 5.75mm.
the deck height # may be a bit off (high) i had to use clay, the solder trick wouldn't work for me. even if i swap out my cylinder base gaskets, how much extra compression is a .5 mm decrease gonna get me. i was wondering if any rebuilders out there have seen these #'s. i'm not building a race car. but maybe not too many are using stock e cams. thanks
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bob 1972 E pos correction: expensive pos someday.... "shut up and drive!" |
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03-28-2010, 06:37 AM
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In a 2.7 engine .5mm gives about a half point compression increase.
-Andy
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72 Carrera RS replica, Spec 911 racer |
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03-28-2010, 06:42 PM
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