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Join Date: Nov 2002
Location: Kansas City
Posts: 715
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Tight wrist pin on one cylinder..problem?
This a question I'm afraid to ask, but when I rebuilt my 2.0S motor a year ago I remember one of the wrist pins went into the piston pretty hard due to a nick I made when dissasembling the pin circlips.
Anyway, somehow during the rebuild I forgot about that and assembled the motor and have been running it ever since. Runs great after 5000 miles, but I've always wondered. Logic tell's me it shouldn't matter much since the pin rotates freely on the end of the rod, so whey should it need clearance to rotate in the piston itself? However, my logic is generally flawed.. Could something bad be happening to that pin/piston?
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Current: 1975 911S --Chocolate brown Past: 1967 911S --Bahama Yellow 1990 C2 Targa --Silver 1973 914 2.0 --Delphi Green |
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02-19-2007, 09:21 AM
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Life moves pretty fast.
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No worries the pins aren't meant to rotate in the pistons, that's why the bearing is in the rod end. On some engines I've worked on the pin is a real tight fit in the piston and I have to heat the piston to get them in.
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Twin plugging, you know it makes sense 
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02-19-2007, 01:18 PM
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Cool, that's what I thought.
Thanks!
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Current: 1975 911S --Chocolate brown Past: 1967 911S --Bahama Yellow 1990 C2 Targa --Silver 1973 914 2.0 --Delphi Green |
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02-20-2007, 02:40 PM
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Actually, the Porsche design is full-floating, meaning the piston bore as well as the small end of the con rod are bearing surfaces. Having two bearing surfaces spreads the load and reduces overall friction loss.
If the pin isn't free to rotate in the piston, the engine will still work. In effect, your situation is like most cars. However, in those cases the rod is pressed into the con rod (fixed) and the piston pin boss provides the bearing surface (semi-floating). The piston boss has a larger bearing surface and access to more lube oil than the smaller con rod bushing. I would prefer that situation over what you have now. The engine guru's can probably make the definitive call. Sherwood PS: Since the aluminum piston expands at a greater rate than the steel piston pin, everthing might be copasetic under normal operating temperatures. Last edited by 911pcars; 02-21-2007 at 10:45 AM.. |
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02-21-2007, 10:41 AM
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Hmmm..
Well, I guess there's not a lot I can do about it now. Would the only ill effect possibly be increased rod bushing wear?
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Current: 1975 911S --Chocolate brown Past: 1967 911S --Bahama Yellow 1990 C2 Targa --Silver 1973 914 2.0 --Delphi Green |
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02-21-2007, 04:48 PM
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Quote:
Sherwood |
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02-22-2007, 09:47 AM
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