How to Adjust Valves on a Gasoline Engine?
3 Answers
When the first cylinder reaches top dead center on the compression stroke, the exhaust valve of the fourth cylinder has not yet closed, and the intake valve has just opened—this is known as valve overlap. During adjustment, turn the adjusting screw while inserting a feeler gauge between the valve stem end and the rocker arm. Move it back and forth until you feel slight resistance, which indicates the proper setting.
I've been repairing cars for over a decade, and adjusting valves is second nature to me. The key is to wait until the engine is completely cooled down before starting, as thermal expansion can affect measurement accuracy. First, remove the valve cover, locate the top dead center position of the corresponding cylinder, and measure the valve clearance with a feeler gauge. The ideal clearance is usually between 0.20 to 0.30 millimeters—too tight and you risk burning the valve, too loose and it'll cause a ticking noise, affecting performance. When adjusting, use a wrench to turn the adjustment screw bit by bit, gently, without applying too much force to avoid breaking anything. After adjusting each valve, measure it again to ensure precision. Different car models may vary slightly; Japanese and American cars have slightly different parameters. Remember to check every 20,000 kilometers or so to avoid sudden breakdowns. For safety, wear gloves and clear the area around the engine before starting.
I often discuss car maintenance with my friends. Adjusting valves sounds sophisticated but isn't actually hard to master. Just prepare a socket wrench and feeler gauge, and start when the engine cools down. After removing the valve cover, locate the top dead center of cylinder 1. If the gap measured by the feeler gauge is incorrect, adjust the screw or shim until it slides in just right. Work on only one valve at a time to avoid messing up the positions. The valve clearance directly affects the engine's combustion efficiency—too large causes noise, too small accelerates wear. Many older cars shake badly because this is neglected. DIY saves some money, but take it slow and don't rush. Tools can be bought online, so give it a try.
