A mechanic friend of mine gave me a bunch of used shims in 3 sizes. I assume its okay to install used shims or he would not have given them to me. But I can see a concave surface where the rocker cut into them and another spot where the valve stem cut in a little. That is why I think they should be replaced as a wear item and proper seating of the rocker may be inhibited. The shims have to come out to remove the rocker to remove the lifter. Since they have to come out anyway, shouldn't they be replaced?

The lifters have only a little travel. To be properly set, there is a correct shim size for each lifter and it has to be measured after it is installed. You install a shim of whatever size then crank the starter for 30 seconds to fill the lifter, and then measure it with a special tool. You have to change the shim to be in the middle of the go/no-go gauge. If your mechanic said use the same shims he must mean to get a base reading then change the shims as necessary. That sounds plausible. But if they are good in height with the old shim, do you leave it in place or change it to a new shim?

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Steve
1985 Mercedes 500SL Euro (Gray market)
1995 BMW 520i Euro (Gray market)
1992 BMW 525it Wagon
1994 Honda Del Sol Si