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A valve job is the colloquial term for resurfacing the mating surfaces of the poppet valves and their respective valve seats that control the intake and exhaust of the air/fuel mixture in four stroke internal combustion engine, replacing valve oil seals, replacing any deficient valve springs, and otherwise bringing the components of a cylinder head up to manufacturer’s spec. [1] A ...
Valve seats are often formed by first press-fitting an approximately cylindrical piece of a hardened metal alloy, such as Stellite, into a cast depression in a cylinder head above each eventual valve stem position, [1] and then machining a conical-section surface into the valve seat that will mate with a corresponding conical section of the ...
Access through the cylinder bore is restricted for machining the valve seats, or for inserting angled valves. An even more serious restriction is de-coking and re-grinding valve seats, a regular task on older engines. Rather than removing the cylinder head from above, the mechanic must remove pistons, connecting rods and the crankshaft from ...
Stellite alloys were a major improvement in the production of poppet valves and valve seats for the valves, particularly exhaust valves, of internal combustion engines. By reducing their erosion from hot gases, the interval between maintenance and re-grinding of their seats was dramatically lengthened.
Longevity, as demonstrated in early automotive applications of the Knight engine. Prior to the advent of leaded gasolines, poppet-valve engines typically required grinding of the valves and valve seats after 20,000 to 30,000 miles (32,000 to 48,000 km) of service. Sleeve valves did not suffer from the wear and recession caused by the repetitive ...
Grinding of valves to fit was once a regular garage task, as was light re-cutting with hand tools, when cast iron seats were common. Once steel seat inserts came into use, either as a result of the switch to unleaded petrol in the 1970s or fitted into high-performance aluminium heads, machining of heads and the replacement of seats became ...
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Some tappets had a threaded adjuster, but simpler engines could be adjusted by grinding down the ends of the valve stem directly. As the tappet adjustment always consisted of expanding the clearance (re-grinding valves into their valve seats during de-coking makes them sit lower, thus reducing the tappet clearance), adjustment by shortening the ...
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