How to adjust the valves of an eight-cylinder engine?
3 Answers
Eight-cylinder engine valve clearance adjustment method is to adjust the valve clearance according to the firing order of 1-5-4-2-6-3-7-8. Additional information is as follows: 1. Function of valves: Specifically responsible for introducing air into the engine and expelling exhaust gases after combustion. In engine structure, they are divided into intake valves and exhaust valves. The intake valve's function is to draw air into the engine to mix with fuel for combustion; the exhaust valve's function is to expel the combusted exhaust gases and dissipate heat. 2. Composition of valves: Valves consist of a valve head and a stem. The valve head operates at very high temperatures (intake valve 570~670K, exhaust valve 1050~1200K) and also withstands gas pressure, valve spring force, and the inertial force of transmission components, with poor lubrication and cooling conditions. Therefore, valves must possess certain strength, stiffness, heat resistance, and wear resistance. Intake valves are generally made of alloy steel (chromium steel, nickel-chromium steel), while exhaust valves are made of heat-resistant alloy (silicon-chromium steel). Sometimes, to save on heat-resistant alloy, the exhaust valve head is made of heat-resistant alloy, and the stem is made of chromium steel, with the two parts then welded together.
I've been driving my vintage car with a V8 engine for many years, and adjusting the valves is pretty much routine maintenance. Specifically, you need to warm up the engine first—let it idle for a few minutes so the metal expands to operating temperature, but be careful not to burn yourself for safety. Then, turn off the engine, remove the valve cover, and find a good spot to start adjusting. For an eight-cylinder engine, there are usually sixteen valves, and you'll need to adjust them one by one. Use a feeler gauge to measure the clearance—the standard is around 0.10 to 0.15 millimeters, but always check your car's manual to be sure. Rotate the crankshaft to the top dead center (TDC) position to adjust the first cylinder, loosen the lock nut, adjust the screw until the clearance is correct, and then tighten it. Repeat for all cylinders—don’t skip any, or the engine might make a ticking noise when running, and in severe cases, it could even burn out the valves. As for tools, just have a feeler gauge and a small wrench handy; beginners might want to ask a friend to help hold things steady. After the adjustment, warm up the car and test for any unusual noises. Regular checks can help you avoid major repairs.
As a mechanic with years of experience, let me share how it's done. Adjusting the valves on an eight-cylinder engine isn't difficult, but requires methodical steps. First, warm up the engine at idle for five minutes, then shut it off to prevent burns. Address each valve individually: use a feeler gauge to measure the clearance, aiming for an ideal value around 0.12mm (check specific model specifications). Starting from the first cylinder, locate top dead center, then adjust the screw or shim to ensure precise clearance. After each adjustment, listen for the sound—if too loose, you'll hear excessive noise during operation; if too tight, the valve may stick. Wear gloves and safety goggles throughout, and don't rush. Improper adjustments can degrade engine performance or cause permanent damage. We recommend checking every 15,000 kilometers to maintain optimal operation.
