Valve guides protect and align valves in combustion engines, regulating temperature and preventing oil leaks. They are designed to outlast valves and require proper lubrication and oil changes. Worn guides can cause engine problems, and repair options include pressing out old guides and installing new ones or knurling.
A valve guide is a small tube, usually made of metal, designed to cover, protect, and align one or more valves in a combustion engine. Perhaps most commonly seen in automobiles, they are an important part of the engines of many gasoline-powered vehicles and devices. The main idea is to keep the valves running into the exhaust and intake plenums supported and positioned properly, but the guides usually also play a big role when it comes to regulating temperature and preventing things like oil leaks. Most guides are designed to outlast the valves they protect, and are generally built to be very durable. With proper engine care and regular oil changes, these devices should go unnoticed. However, if the casing wears out or ages prematurely, big problems can result: engines often overheat, car hoods can start to smoke, and the whole system can stall until things are fixed. Repair options are usually quite simple, although the process can be somewhat complicated for the untrained.
Basic concept and how it works
Combustion engines are usually made up of many different parts and are typically designed to transport energy and power fairly quickly from one place to another to facilitate continuous movement. Most engines contain a series of valves, which are basically connections between parts that allow or, alternatively, control the passage of fluids, air, or steam. Over time, the valves can wear out; they are usually made of several interlocking parts and tend to fall over if not fastened firmly. This is the main idea behind the valve guide: hold the valve, protect it, and make sure it doesn’t get a chance to shift or lose traction.
In general, the guides are designed to fit over the valve stems with a minimal amount of clearance and use oil that seeps through the guide seal to lubricate it. This oil has the task of controlling the high temperatures of the valve stem through the combustion process. In aluminum head applications, the guides also help prevent heat damage to the head. The ultra-high heat generated by the combustion chamber is radiated away from the valve stem by the guides.
When is it used
The guides are only used for engines that use a pushrod type camshaft. For the overhead valve type of engines, the guide is not used, since the cam actually actuates the valves and pushrods are not needed. The typical valve guide is designed to outlive the engine and therefore will never require repair. With proper lubrication and scheduled oil change intervals, guides should remain in peak operational shape.
Aging and Disintegration
However, no build is foolproof and in some cases the guides will wear out. As the guide wears, the valve stem begins to loosen and oil can leak into the combustion chamber. This creates smoke and a loss of engine power. The problem is usually fairly easy for a mechanic to diagnose, but the repair can be more of a challenge.
repair options
Perhaps the most complete method of repairing a worn guide is to press the old guides out of the head and install new guides. This repair method is risky and many heads are damaged beyond repair; It also tends to be quite expensive. Once it is successfully ejected, the old guide is replaced with a new guide that is pressed into place. Once the new valve guide is in place, it is trimmed to fit and dressed to receive a new valve. This procedure is mainly used on aluminum heads.
A method known as knurling is usually a more popular option, although it is not always as precise. This procedure builds the guide out of metal and additional materials, and then re-mills it to the proper size. Once the guide is repaired using the chosen method, the guide seal is replaced. This is a small rubber cup-shaped component that pushes down on the valve stem. The seal is pushed over the boss of the guide cast in the head and prevents excess oil from entering the guide.
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