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gestalt1's Avatar
Join Date: Feb 2003
Location: chicago
Posts: 1,079
deck height problem

so i dry assembled the top end of my 3.2ss and checked the deck height and got 1.75mm. i measured with calipers the deck ht from the piston edge to the top of the cylinder and set it at 1mm with (2) .25mm and (1) .5mm copper gaskets. the heads were chamfered for 100mm cylinders and i am using 98mm cylinders. when the piston is at TDC the chamfer is giving an extra 1mm of clearence. is it ok to set the the deck ht to .25mm in this situation? i would leave a .25mm copper gasket so the actual deck ht would be 1mm. the piston would be only .25mm from the top of the cylinder and the extra chamfer space would be providing the clearence. i realize the chamfered heads are not optimal for these cylinders but the chamfer measures only .75mm over the edge of the cylinder. the compression ratio calculated to 10.02:1 with .25mm deck ht (=1mm with chamfer area). i do have twin plug heads and 10:1 is what i'm shooting for.
Old 02-03-2006, 08:12 PM
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Join Date: Jun 2004
Location: Rio Rancho, New Mexico
Posts: 1,326
Looks to me like you did all your calculations correctly.
You are interested in how close the piston comes to the head and you have addressed that.
The twin plugging should handle the compression.
I'm not sure how the larger 100mm head will work with the smaller cylinder. It's 1mm all around less surface to seal things up.
Plus that little space putting pressure directly between the head and cylinder. Maybe I'm seeing something of no consequence.
Others may have experience or more knowlege regarding this.
'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 02-03-2006, 09:52 PM
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Join Date: Mar 2005
Posts: 743
Sounds OK to me.

But do check exhaust valve clearance..

Kind regards
Old 02-04-2006, 03:20 AM
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