How to Test for Bad Valve Guide Seals
The valve guides in any auto engine suffer a tremendous amount of punishment because they have to move vertically within their guides whenever the engine runs. The up and down flex of the valves not only wears the valve stem and valve guides, but it can allow excess heat to burn out the valve seals. The valve seals, usually made of hardened rubber, must keep oil from passing down the valve stem and into the combustion chamber. Once valve seals have deteriorated or burnt out, they allow excess oil to be burned in the cylinder, which passes excess carbon through the valve faces and out through the exhaust.
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Things You'll Need
- Floor jack
- Jack stands
- Socket set and wrench
- Shop light
- Compression gauge
- Exhaust gas analyzer (if applicable)
- Assistant
Instructions
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Place the vehicle in park or neutral with the emergency brake set. Start the engine and let it warm to normal operating temperature. Rev the engine a few times and look back at the exhaust tailpipe. If you notice any blue-white smoke exiting the tailpipe, it can indicate excessive oil consumption, caused by worn or defective oil seals. Copious amounts of such smoke can also point to worn valve guides and stems, in addition to bad seals.
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Raise the vehicle with the floor jack and place four jack stands under the frame near each wheel. Use a shop light to examine the condition of the muffler and catalytic converter. Any oil seepage from the muffler drain hole or the catalytic converter seams or joints means that worn seals might have allowed unburned oil to pass through the combustion chambers. A black or discolored catalytic converter that has a burnt, rotten egg smell means that it has clogged and destroyed the palladium pellets inside.
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Lower the vehicle to the ground. Disconnect the main ignition coil wire from the coil. Remove all the spark plugs with the plug socket and wrench, making sure to keep the plug wires in the proper location. Attach a compression gauge at the spark plug hole, and instruct an assistant to turn the engine over seven or eight times by turning the ignition key to the "start" position, then stopping on the last (eighth) revolution. Record the psi (pounds per square inch) reading on the gauge.
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Test all the cylinders with the compression gauge. Compare your numbers with the manufacturer's specifications in your owner's repair manual. Any reading higher than normal indicates that blow-by carbon has built up on the top of the pistons. The probable cause is bad valve seals and guides.
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Start the engine. Examine the PCV (positive crankcase ventilation) valve hose where it connects to the valve cover and the intake manifold. Look for any blow-by seepage of oil either dripping from the hose connections or blue-white smoke passing through the connections.
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Look at the EGR (exhaust gas recirculation) valve, sitting on the intake manifold or near the throttle body. Examine it for a black appearance, or any oil dripping from its connection hose or diaphragm. Worn or broken seals will cause oil to be sucked up through the engine vacuum and contaminate the EGR valve.
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Make note of any engine stumbling after the vehicle has had a complete and successful tune up. Refer to your compression test numbers for any cylinder that reads 30 lb. or more under specifications. An engine miss that can not be attributed to a fuel or electrical problem could point to a burned valve face. If a seal has become broken or worn it will allow excessive heat to contact the valve face, particularly the exhaust valve, and cause a lean misfire in the engine.
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Tips & Warnings
Use an exhaust gas analyzer to determine how much HC (hydrocarbons) are being emitted from the exhaust. Excessive HC emissions can point to unburned carbon in the exhaust, caused by faulty valve seals. Your smog emission test facility can also determine if the HC readings are beyond specifications. The vehicle will fail the smog test if the exhaust gas analysis exceeds limits.
References
- Photo Credit cylindre et piston image by Unclesam from Fotolia.com
