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process. They found that by reaming all the valve guides in a head to one standard size (typically 0.008 in. diametrically oversized), and installing remanufactured engine valves having stems that are also oversized, a typical engine head can be remanufactured in much less time. Since the reaming
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The clearance between the inner diameter of the valve guide and the outer diameter of the poppet valve stem is critical for the proper performance of an engine. If there is too little clearance, the valve may stick as oil contaminants and thermal expansion become factors. If there is too much
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Valve guides are typically shaped in a tube with a flare at one end. Their replacement involves removing the worn part by driving it out with a hammer and specifically-shaped punch. Installation may involve
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process leaves the valve guide with a much better surface finish and shape than typical replacement guides, and since the oversize valves often have chrome plated stems, remanufacturers also discovered that
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Studies have been conducted which show that through the proper selection of the reamer and reaming process, valve guides can be quickly and efficiently reamed to a consistently repeatable size.
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Guides also serve to conduct heat from the combustion process out from the exhaust valve and into the cylinder head where it may be taken up by the cooling system.
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seal is fitted over the top of the valve guide. These may wear or stiffen with age, so are usually replaced whenever valves are removed for servicing.
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The upper part of the valve stem, within the rocker box, is lubricated by oil. If this oil travels unchecked along the valve stem, engine
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Over time, the inner diameter of the valve guide and the outer diameter of the valve stem may become worn.
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alloys; a balance between stiffness and wear on the valve is essential to achieve a useful service life.
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clearance, the valve may not seat properly and excessive oil consumption can occur.
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are cylindrical metal bushes, pressed or integrally cast into the
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In the 1980s, many U.S. production engine remanufacturers began
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valve guides, rather than replacing them, as part of their
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16:Combustion engine component
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301:Mechanisms (engineering)
249:"Custom Engine Valves"
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272:. Cal Grinding
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215:Replacement
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290:Categories
276:2017-02-26
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236:References
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99:March 2007
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167:Oil seal
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