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Old February 5th, 2018, 04:26 PM   #42
DannoXYZ
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Name: AKA JacRyann
Location: Mesa, AZ
Join Date: Dec 2011

Motorcycle(s): CB125T CBR250R-MC19 CBR250RR-MC22 NSR350R-MC21 VF500F CBR600RR SFV650 VFR750F R1M ST1300PA Valkyrie-F6C

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MOTY - 2018, MOTM - Nov '17
Yep, as valve & seats wear, their contact area ring increases in width. This spreads out spring-force and lowers pressure at contact, leading to less sealing. Lapping further increases this contact area. FSM dictates minimum & maximum seat contact width. Aim for the narrow end of range first with valve-job machining (3-angles). Then lap just slightly to improve sealing.

With modern machinery, it's not any more difficult or expensive to cut fully-radiused valve-seats. Then cut flat seating area of minimum width to preserve improved flow. Much, much better than 5 or 7 or 9-angle valve-jobs. Also beryllium-copper seats shown transfers heat much, much faster than steel, reducing wear and greatly enhances exhaust-valve lifespan.

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