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Alan L's Avatar
 
Join Date: Apr 2006
Location: New Zealand
Posts: 1,804
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 SC (Been gonna sell for 7 yrs), 82 930 (track) - Stock except for RarlyL8 race headers, 22/28 T bars, Digi WUR (currently in a box), Rarlyl8 Zork, modified 3LDZ, 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.

Last edited by Alan L; 07-11-2011 at 04:53 PM..
Old 07-11-2011, 04:24 PM
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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
Old 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 SC (Been gonna sell for 7 yrs), 82 930 (track) - Stock except for RarlyL8 race headers, 22/28 T bars, Digi WUR (currently in a box), Rarlyl8 Zork, modified 3LDZ, 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.
Old 07-12-2011, 11:17 AM
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Old 07-12-2011, 11:17 AM
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