It is possible to adjust valve clearance with the camshaft in place.
Not very easy, but doable for the experienced DIY'er:
Check valve clearance
-Wrench with 10mm socket & 16mm spark plug socket
-Depending on its state: valve cover gasket
Adjust valve clearance
-2 large (10mm wide tip) screwdrivers; as long as possible
-1 medium (6mm tip) screwdriver also not too short
-very tiny screwdriver
-Measure valve clearance (e.g. Haynes does explain this very well, or see this: http://www.mazda626.net/index.php?s=&s...t&p=229085)
-If one or more valve clearances are out of tolerances remove the shim using the procedure below:
*Have the cam above the shim pointing upwards for maximum clearance
*Press the tappet down as far as possible with the first large screwdriver
*Put the tip of the second large screwdriver between the tappet and the camshaft to block the tappet in the lowered position
*Remove the first big screwdriver
*With the tiny screwdriver, loosen the shim from the tappet (there's some suction of oil between the shim and the tappet), then pull it
further out with the magnet pencil/bar
*You can't completely remove the shim, because the second large screwdriver is blocking the way
*Now, with the medium screwdriver, press the tappet down from the other side
*Remove the second large screwdriver which was between the camshaft and the tappet
*Now completely remove the shim with the magnet pencil/bar
*Calculate the new shims size and buy the correct size at the dealership (probably the only place to get it)
*Press the tappet down again on the back side using the medium screwdriver
*Insert the new valve shim and push it into the tappet as far as possible (possibly 80-90%)
*Now remove the medium screwdriver and press the shim in totally
-Do this for every valve which is out of tolerance
-Put the valve cover back on, and you're done!
The procedure will be a pain in the ass the first time you do it. It
took me 30 minutes before I found out this procedure myself and was
able to remove the shim. Next shims were much more easy to remove!
Because the insertion of the shim is so much easier than the removal,
you don't have to be too afraid of removing the shim, withour being
able to put it back in....