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Piston orientation
Is there a right and wrong upside/downside for installing the 930 pistons? They look symmetrical, and I can't find anything in Waynes book or this forum on a 'proper' orientation.
Thanks 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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09-11-2014, 03:13 PM
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3 restos WIP = psycho
Join Date: Feb 2005
Location: North of Exit 17
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Mahles have offset pins, so yes. JEs do not.
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- 1965 911 - 1969 911S - 1980 911SC Targa - 1979 930 |
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09-11-2014, 03:26 PM
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There should be a mark on top of the piston that you make sure points toward the flywheel side of the engine.
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09-11-2014, 03:44 PM
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Preferred pronoun:Maestro
Join Date: Sep 2012
Location: Group W Bench
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On stock pistons there's a small mark on the top that goes toward the flywheel. Yes, there's more than one mark, but when you look closely it's pretty evident which one represents the flywheel side.
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When in doubt, use overwhelming force. |
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09-11-2014, 03:45 PM
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I'm guessing it is the squiggly mark (circled) rather than the marks in the square?
And it faces to the flywheel? Thanks 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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09-11-2014, 04:34 PM
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Preferred pronoun:Maestro
Join Date: Sep 2012
Location: Group W Bench
Posts: 11,359
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^^^ Good guess ^^^
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When in doubt, use overwhelming force. |
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09-11-2014, 04:46 PM
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Glad I asked. Odd there is nothing in Waynes book - it talks about the valve pocket domes etc.
The offset Kenik mentioned measures out at about 1.5mm. This is a slightly used set of P&Cs I am installing - but they have been disassembled. Interestingly it has 2 sets of ID marks on the P&Cs - ie it has been disassembled at least twice before, and the numbering ID marks are different - eg one P/C has marks #2 and #5 on it. Thinking further, if you swapped a P/C from one side to the other, you would have to rotate the piston 180 Deg, or else the mark to the flywheel would now be pointing to the fan. Thanks for the help. 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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09-11-2014, 05:03 PM
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While I got your guys attention, maybe you can clear up another dilemma. Waynes book says the compression rings should be installed with 'the gaps located roughly opposite each other, and not lined up with the piston wrist pin'. While the oil ring gap goes to the top. As in the pic (red arrow). To me, this means the compression ring gaps (green/blue) have to be located in the picture, in line with the wrist pin?
I think previously I have just ignored the wrist pin advice. But I can't see how that and the picture can both be correct. Or have I missed something? Thanks 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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09-11-2014, 05:45 PM
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Preferred pronoun:Maestro
Join Date: Sep 2012
Location: Group W Bench
Posts: 11,359
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Quote:
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When in doubt, use overwhelming force. |
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09-11-2014, 05:52 PM
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Join Date: Jul 2006
Location: S. Florida
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Here are the ring gap positions Porsche recommends from the factory maqnual.
 I installed mine in these positions and the motor runs great. |
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09-11-2014, 06:16 PM
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Chain fence eating turbo
Join Date: Dec 2008
Location: Austin, TX
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^^^ same here, no blowby
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Cory - turbo'd '87 C3.2 Guards/Blk, 3.4, 7.5:1 CR P & C's, 993SS cams, Borg-Warner S366 turbo @ 1.2-1.5 bar, depending on mood  , Treadstone full bay IC, 70mm TB, TiAL F46 WG, HKS 1 1/2" BOV, twin 044 pumps, MicroSquirt AMP'd w/GM smart coilpack, Bilstein coilovers, Tramont wheels (285's rr, 225's frt), Big Reds frt, 993 rr., tower brace, MOMO wheel
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09-11-2014, 06:19 PM
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So the Porsche manual is slightly different to Waynes book - which shows them at 3 and 9 o'clock. I doubt it makes much difference to anything, since they walk to wherever they want to go over time. But I am just curious about the apparent discrepancy between picture and text in Waynes book. And also why you set out to avoid aligning with the wrist pin. Porsche seem to have done the same with their 4/10 o'clock.
Regards 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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09-11-2014, 06:52 PM
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I'm not sure and can only guess why the ring gaps should not be in line with the wrist pins. I am sure that Porsche knows more about this than Wayne so I wouldn't try to over think it or second guess what the factory manual says.
The ring gaps may migrate for a while during break in with a new motor but I think they take a set and stay where they are once it is fully broken in. I'd say that's between 500 and 1000 miles depending how the motor is run during the first 1000 miles but I'm not an expert. |
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09-11-2014, 07:13 PM
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1985 Porsche 930
