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Join Date: Mar 2003
Location: 24 miles from Lime Rock Park. 1 light, 8 Horse Farms, 114 Turns
Posts: 137
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Piston Pin Offset
When I took the Pistons and Cylinders off of my 964-3.6 I noted the direction of the piston by recording what direction I slid the pin, so I'm pretty confidant I know how they came out. Seems to be small (E) marks on the upper sides
The piston pins are offset in the piston, and the offsets are on the high side of both banks. With clockwise rotation I would expect 4-6 To be on the upside, and 1-3 to be offset on the underside. Maybe I'missing something. How is it supposed to be designed/installed? Thanks, Alan |
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06-11-2009, 06:18 PM
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'66 911 #304065 Irischgruen ‘96 993 Carrera 2 Polarsilber '81 R65 Ex-'71 911 PCA C-Stock Club Racer #806 (Sold 5/15/13) Ex-'88 Carrera (Sold 3/29/02) Ex-'91 Carrera 2 Cabriolet (Sold 8/20/04) Ex-'89 944 Turbo S (Sold 8/21/20) |
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06-12-2009, 05:56 AM
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Location: 24 miles from Lime Rock Park. 1 light, 8 Horse Farms, 114 Turns
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Thanks John
Perfecto!
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06-12-2009, 06:29 AM
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Location: Portland Oregon
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The 964 (and many 993) 3.6 engines unfortunately use the same offsets on ALL pistons.
This means that 3 of them have the correct offsets and the others are wrong; its been that way since 1990,..... It practically took an "Act of God" to get Mahle to finally correct this on the latest 3.8 P/Cs'.
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Steve Weiner Rennsport Systems Portland Oregon (503) 244-0990 porsche@rennsportsystems.com www.rennsportsystems.com Last edited by Steve@Rennsport; 06-12-2009 at 10:39 AM.. |
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06-12-2009, 10:36 AM
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Max Sluiter
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Steve, after reading the thread linked above and then your comment, I am wondering if the early cars had side-specific piston offsets. Were the offsets on 90mm Mahles both to the exhaust side or were the offsets working together to produce the same effect on both cylinder banks?
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1971 911S, 2.7RS spec MFI engine, suspension mods, lightened Suspension by Rebel Racing, Serviced by TLG Auto, Brakes by PMB Performance |
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06-12-2009, 12:49 PM
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Max Sluiter
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Wouldn't cam timing be slightly different (relative to the crankshaft position) between the cylinder banks if the piston pin offsets were both on the bottom? I suppose that is why cams are timed according to TDC on 1 and 4 cylinders separately.
I do realize .8mm is not going to do much.
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1971 911S, 2.7RS spec MFI engine, suspension mods, lightened Suspension by Rebel Racing, Serviced by TLG Auto, Brakes by PMB Performance Last edited by Flieger; 06-12-2009 at 03:56 PM.. |
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06-12-2009, 03:53 PM
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The only pistons that I recollect have the same offsets are the 3.6, 100mm ones and most 3.8 102mm versions.
Early stuff like your 90mm ones had side-specific offsets,.... Cam timing is not affected but piston & cylinder wear are affected on the "wrong" side of those P/C sets.
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Steve Weiner Rennsport Systems Portland Oregon (503) 244-0990 porsche@rennsportsystems.com www.rennsportsystems.com |
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06-12-2009, 07:47 PM
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Max Sluiter
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Thanks for the interesting information.
So, the 90mm Mahles have the offset to reduce piston slap on both sides? Or is it the greater push on the power stroke?
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1971 911S, 2.7RS spec MFI engine, suspension mods, lightened Suspension by Rebel Racing, Serviced by TLG Auto, Brakes by PMB Performance |
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06-12-2009, 08:59 PM
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Indeed, the 90mm Mahles do have offset pins, specific for each side, that reduce both thrust losses and friction on the power stroke,....
Piston skirts last longer as well as reduced top ring land wear.
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Steve Weiner Rennsport Systems Portland Oregon (503) 244-0990 porsche@rennsportsystems.com www.rennsportsystems.com |
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06-12-2009, 10:17 PM
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Steve, wow, I didn't know that.
Tom Butler, do you have a photo of the top of a 90mm Mahle handy?
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'66 911 #304065 Irischgruen ‘96 993 Carrera 2 Polarsilber '81 R65 Ex-'71 911 PCA C-Stock Club Racer #806 (Sold 5/15/13) Ex-'88 Carrera (Sold 3/29/02) Ex-'91 Carrera 2 Cabriolet (Sold 8/20/04) Ex-'89 944 Turbo S (Sold 8/21/20) |
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06-13-2009, 05:33 AM
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1971 Porsche 911S
