 ARRRGGGGGGG! KB p/c's, New pistons are too small for slightly used cylinders... |
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| Bartlett 914 |
 Sep 11 2006, 11:44 AM
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#21
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Advanced Member  Group: Members Posts: 2,216 Joined: 30-August 05 From: South Elgin IL Member No.: 4,707 Region Association: Upper MidWest  |
QUOTE(ptravnic @ Sep 11 2006, 09:06 AM)  The skirt clearance ended up being within range. That was good news. The mechanic was looking at the gap between the crown of the piston and the cylinder. For some reason, the KB's measured ~ 95mm at the crown of the poston, and ~ 96mm at the skirt. I guess thats just the way the KB's are... This is interesting! Out of curiosity, I just measured a piston and cylinder that is out of an old 2.0 . I always thought that pistons were made intentionaly out of round. I measured 3.767" ROUND (not ovaled) at the top of the piston. I measured 3.697 at the skirt. That is a .021" difference! My cylinder measured 3.702 throughout. Using the skirt measurement I get .005" clearance. I assume this means that I cannot hone and reuse them. Is this correct or is the .003" more for the KB's and not Porsche pistons? Mark |
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| ptravnic |
Sep 11 2006, 11:59 AM
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#22
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Senior Member Group: Members Posts: 1,231 Joined: 27-May 03 From: Chicago, IL Member No.: 747 Region Association: None 
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QUOTE(Bartlett 914 @ Sep 11 2006, 01:44 PM) QUOTE(ptravnic @ Sep 11 2006, 09:06 AM) The skirt clearance ended up being within range. That was good news. The mechanic was looking at the gap between the crown of the piston and the cylinder. For some reason, the KB's measured ~ 95mm at the crown of the poston, and ~ 96mm at the skirt. I guess thats just the way the KB's are... This is interesting! Out of curiosity, I just measured a piston and cylinder that is out of an old 2.0 . I always thought that pistons were made intentionaly out of round. I measured 3.767" ROUND (not ovaled) at the top of the piston. I measured 3.697 at the skirt. That is a .021" difference! My cylinder measured 3.702 throughout. Using the skirt measurement I get .005" clearance. I assume this means that I cannot hone and reuse them. Is this correct or is the .003" more for the KB's and not Porsche pistons? Mark I'll defer to the experts on this one... -pt |
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| smdubovsky |
Sep 11 2006, 12:03 PM
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#23
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Member Group: Members Posts: 331 Joined: 27-September 04 From: Silver Spring, MD Member No.: 2,837 Region Association: MidAtlantic Region |
I *think* my 911 J&Es (and some V8 pistons) were made w/ the top smaller than the skirt. The top takes the most heat and thus expands more (esp w/ turbos). The skirts run much cooler and can run closer tolerances. Been ages though...
SMD |
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