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piston ring gap
I went to insert some new 930 rings in the cylinders. The spec sheet says max wear limit ring gap is 8 thou (0.2mm).
When I insert my new rings in the very top (unworn) and lower part of the bore, I still get 12 thou gap - how does that work? I'm reasonably sure the rings dont come in various sizes. Alan OK, I read the specs wrong - mixed up ring gap and ring clearance specs. 12 thou is in spec - just, for new ring.
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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:-) Last edited by Alan L; 07-11-2011 at 04:53 PM.. |
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07-11-2011, 04:24 PM
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Join Date: May 2003
Posts: 3,346
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On two engines I've rebuilt, I used the old rings because they had smaller end gaps than the new rings I' had bought.
-Andy
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72 Carrera RS replica, Spec 911 racer |
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07-12-2011, 09:51 AM
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On other engines I have done, you haveless than minimal gap and have to grind the ends to open them to minimum spec - with a special ring grinder stone.
So it does seem weird when re-ringing these things you have to start off with more than minimal ring gap - especially for a track machine. Squeezing up the ring gap to the bare minmum (which is usually a secret number to the engine builder) is one of the performance edges builders look for. But not an option here. 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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07-12-2011, 11:17 AM
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