Valve guide

<h2 id="oil-seal">Oil seal</h2>
<p>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 HC emissions will become excessive. To control this, an <a href="/facts/Elastomer/kCSD0udN">elastomeric</a> 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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<h2 id="wear">Wear</h2>
<p>Over time, the inner diameter of the valve guide and the outer diameter of the valve stem may become worn. Moreover, the valve guide is exposed to high temperatures during operation, which can reduce its hardness and, consequently, lead to deformation under stress. 
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<h3>Reaming</h3>

<p>In the 1980s, many U.S. production engine remanufacturers began <a href="/facts/Reamer/GLdAdalF">reaming</a> valve guides, rather than replacing them, as part of their <a href="/facts/Remanufacturing/QS85dlNX">remanufacturing</a> 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 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 <a href="/facts/Valve_train/PMAR1vSR">valve train</a> warranty issues are virtually eliminated.
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<h3>Replacement</h3>
<p>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 <a href="/facts/Shrink-fitting/uF83ppIn">shrink-fitting</a>, heating the cylinder head and cooling the valve guide so as to ease insertion, then driving the new guide in quickly with a press or a hammer. Once the parts return to room temperature the new valve guide will be solidly in place and ready to be <a href="/facts/Reamer/GLdAdalF">reamed</a> and <a href="/facts/Honing_(metalworking)/qEbVkYAD">honed</a> to proper diameter.
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<h2 id="references">References</h2>

<ol>
<li id="fn:1"><p>Singh, Baljeet (2024). "Tribomechanical, and microstructural morphological analysis of nitride ferrous powder metallurgy composites for enhanced automotive valve guide performance". Journal of Materials Research and Technology. 31: 6–25. doi:10.1016/j.jmrt.2024.06.001 – via Elsevier Science Direct. <a href="https://www.sciencedirect.com/science/article/pii/S2238785424013127" target="_blank">https://www.sciencedirect.com/science/article/pii/S2238785424013127</a> <a href="#fnref:1" class="footnote-back-ref">↩</a></p></li>
<li id="fn:2"><p>"What is Valve Guide". BLUE Powder Metallurgy. Retrieved 17 February 2025. <a href="https://powdermetallurgy.com/what-is-valve-guide/" target="_blank">https://powdermetallurgy.com/what-is-valve-guide/</a> <a href="#fnref:2" class="footnote-back-ref">↩</a></p></li>
</ol>

Valve guide open-in-new

Valve guide