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cylinder wear tolerances

Could someone fill me in on cylinder wear tolerances on stock 1996 to 1998 993 cylinders.
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Old 09-29-2010, 01:06 AM
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I would kindly recommend measuring your piston to cylinder wall clearances (in several places).

The cylinders "ovalize" more than they actually wear unless its swallowed a load of dirt from a bad air filter.
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Old 09-29-2010, 11:31 AM
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The factory wear limit for cylinders is generally 0.1 mm above nominal size. For a 100 mm cylinder the wear limit would be around 100.1 mm. As Steve says, you rarely find a cylinder worn above the wear limit. The ovality limit is 0.04 mm and is more likely to be a problem than overall wear. Matching the piston diameter to the cylinder diameter to achieve proper clearances is also important.
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Old 09-29-2010, 12:50 PM
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What happens if a piston is used that has smaller clearance to the cylinder walls then normal. Not jamed in there but half the recommended clearence.

Chris
73 911 E
Old 10-03-2010, 05:51 PM
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If it is at the low limit it should be OK but any tighter then you run the risk of scuffing and early failure when it gets hot.
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Old 10-03-2010, 07:56 PM
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Actually the greater danger with Nikasil cylinders is to cold seize a piston in the cylinder, the clearances open up quite a bit as the cylinder heats up. I have had good luck running the skirt to wall down to.0011 inch with JE pistons with a hard dry film lubricant coating on the skirts in Nikasil cylinders.

aws
Old 10-04-2010, 09:23 PM
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From the 993 Tech Spec book

Engine M64/05/06/07/08
Play: Cylinders-Pistons 0.02 - 0.03 (new condition)

Engine M64/20 RS
Play: Cylinders - Pistons 0.04 - 0.05 (new condition)

And from both the 993 & 964 Factory Workshop Manuals
Cylinder-to-piston clearance 0.02 -0.03
Old 10-05-2010, 02:41 PM
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