I think what is needed here is calipers, not a micrometer.
A micrometer is the "C" clamp shaped measuring device.  It is
far more accurate that you would _ever_ need for valve regulation.
Calipers will work just fine.  Also, a micrometer is built for
measuring thickness; it is not well suited for measuring depth.

Harbor Freight has some very nice digital calipers on sale right
now for like $15.99:

http://www.harborfreight.com/cpi/ctaf/Displayitem.taf?itemnumber=47257

I use this same model at home and at work and have had not problems.
I had the machine shop at my work test it and it is accurate to less
the 1/1000 of an inch -- certainly more than accurate enough for
valve work.  These work just as well as calipers costing several
times the cost.  I like the digital calipers better than the dial
calipers because they're easier to read.  Also, I can convert between
English measurements and metric at the touch of a button.

Hope that helps,
Ray Finch