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1998YZ400F

replacing valves

5 posts in this topic

when putting in the new valves, is it necessary to have the seats cut or can i use valve grinding compound to make them seat properly. i used the compound on my exhaust valves and theyre still good so im assuming its not too bad. just looking for opinions.

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Whenever installing new valves in a used head, the seats need to be refinished, preferably by grinding. Using lapping compound with the new valves, the flat, true condition of the new valve influences the seat, and in that sense, is partly transferred to it. But at the same time, the worn, rounded, overly wide condition of the seat is partly transferred to the new valve.

Lapping is only useful for a final touchup, and ONLY for STEEL valves.

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Basically no, you should get the seats re-cut, otherwise your new valves will wear away a lot quicker because the seat is deformed to the old valve when it was worn.

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