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Registered
Join Date: Mar 2004
Location: Windsor, CT
Posts: 2,119
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How Big can Scratches on a Wrist Pin be?
Is there any acceptance limits for very fine scratches on a wrist pin?
Attached is one of my wrist pins after polishing it with 5000 grit paper. The surface is now highly reflective and highlights a very fine scratch. Note: the polished surface and shop lights really make the scratch visually pop. I can barely notice it when I drag my fingernail across it. I can feel there is something there, but it is certainly not deep enough to catch and impede my fingernail. More like a subtle dip in the road. Normally, if your fingernail doesn't catch, the scratch is very, very shallow. If it does, then it is "measurable".  Anyone know of a limit for defects on a wrist pin?
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Mike '82 911SC, SSI, 22/29 tbars, 22F/22R Adj swaybars, Bilstein Sport, Elephant polybronze & monoballs, Cambermeister bar, turbo tierods, Carrera oil cooler, front brake cooling ducts, Sparco Sprint 5 & Recaro SRD PAX seat, Teamtech harness, DAS Sport rollbar. |
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02-14-2016, 04:33 PM
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Chain fence eating turbo
Join Date: Dec 2008
Location: Austin, TX
Posts: 9,125
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To me, if there's no high metal, it would simply be an oil channel.
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02-14-2016, 07:38 PM
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Agree
Alan
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83 SC, 82 930 (track) - Stock except for RarlyL8 race headers, RarlyL8 Zork, K27-7006, 22/28 T bars, 007 Fuel head, short 3&4 gears, NGK AFR, Greddy EBC (on the slippery slope), Wevo engine mounts, ERP rear camber adjust and mono balls, Tarret front monoball camber adjust, Elgin cams, 38mm ported heads, 964 IC. 380rwhp @ 0.8bar Apart from above, bone stock:-) |
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02-14-2016, 11:42 PM
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It's a 914 ...
Join Date: Jan 2008
Location: Ossining, NY
Posts: 4,704
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Any concern about it being a stress riser that could lead to failure at some point?
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02-15-2016, 04:38 AM
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Given that considerable weight can be removed from the pins by grinding metal out of the underside, I suspect this would not be an issue. The grinding would leave marks equivalent to this in multiple places. That metal is tough as hell.
Alan
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83 SC, 82 930 (track) - Stock except for RarlyL8 race headers, RarlyL8 Zork, K27-7006, 22/28 T bars, 007 Fuel head, short 3&4 gears, NGK AFR, Greddy EBC (on the slippery slope), Wevo engine mounts, ERP rear camber adjust and mono balls, Tarret front monoball camber adjust, Elgin cams, 38mm ported heads, 964 IC. 380rwhp @ 0.8bar Apart from above, bone stock:-) |
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02-15-2016, 09:14 AM
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Registered
Join Date: Mar 2004
Location: Windsor, CT
Posts: 2,119
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Just couldn't do it. After much polishing I can still feel the scratch. Just can't convince myself that a linear groove is ok for the piston hole surface.
JE is shipping me a new pin. |
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02-22-2016, 02:00 PM
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Make sure to compare the weight with your existing pins.
David
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2007 911 Turbo 6-speed, 1984 911 Carrera, 1974 911S, 75 914-6 conversion/project, 2007 Mercedes SL63 AMG, Coyote Powered FFR Cobra |
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02-23-2016, 03:58 PM
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Registered
Join Date: Mar 2004
Location: Windsor, CT
Posts: 2,119
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I will. Interestingly the orignal pins measured within 0.1grams. So I don't expect an issue.
Follow up: new pin is 0.1 gram heavier than the one it replaces. 100.9gm vs 100.8gm. Last edited by VFR750; 02-27-2016 at 04:08 AM.. Reason: Added new data |
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02-23-2016, 04:00 PM
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1984 Porsche 911 Carrera
1974 Toyota Corona 2000 GT
