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Re: sounds stupid but what is a valve adjust and w (archive)

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Posted by John A on January 11, 2002 at 00:07:47:

In Reply to: sounds stupid but what is a valve adjust and what. posted by jimh on January 10, 2002 at 21:33:22:

The E30 M3 is a "mechanical" lifter design, meaning the valves must have clearance to work right. As the engine heats up, there are different temperatures at various places; one of the hottest is the exhaust valves. Because of the different temperatures and the different expansion rates of aluminum vs. steel, there is a specified clearance for each engine designed; in the case of the M3, it`s 0.011 to 0.013 inch. Tighter clearance gives more duration and higher lift. However, if the valves are too tight, they won`t be closed long enough to lose heat through the seat and you`ll burn the exhaust valves. If the valves are too loose, you will lose power due to the lesser duration, plus they will be noisy (clicking sound). There are two opposing wear factors that affect the valve clearance. As the valve wears on the seat, it is able to close deeper, lessening clearance. As the cam wears on the lifter (or tappet), clearance increases. That is why periodic valve adjustments are necessary. Hydraulic lifter designs also have clearance; the difference is that they have a one-way valve that allows oil under pressure to take up the slack. They`re designed so that there`s not enough force from oil pressure to open the valve; rather it only takes up the slack.

does it do thanx

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