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Merging valves and head castings from different sources can be tricky business, as the relationship between the two is intimate, leaving little margin for error. The first fitment issue to check is the valveguides. This is a precise fit, which has to be correct to avoid either excessive oil burning (too loose) or damage to the guides (too tight). For typical pushrod-type cylinder heads, JMS likes to see 0.001-0.0015-inch clearance for the intakes and 0.0015-0.0020-inch for the exhausts. Experienced cylinder-head guys like JMS's Oscar Alvarez can simply feel when it's right. Without any oil, you should be able to wiggle the valve just slightly in the guide with the head of the valve about a half-inch off the seat. Any binding is an indication of a fit that's too tight, requiring the guides to be reamed slightly. Our Powerhouse valves fit just right in the Pro Topline heads. View Related Article
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