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Some are, some aren't. Very early 9N valves (actually, valve tappets) were fixed and the only way to adjust valve clearances was by grinding. Needless to say, that didn't last long. Later design was an adjustable tappet - the tappet body has a locking female thread and a male threaded tappet head screws into it. The tappet head has a hex on it to allow for adjustment. Almost any motor that has been overhauled has most likely had the newer tappet design retrofitted. To adjust them, you'll need a 7/16 open-end wrench about 1/8 thick. Problem is/has been holding the cylindrical tappet body still so as to turn the threaded adjuster. There is a pair of special tools which hook into the holes you observed and lock the tappet from turning. This system sucks. Most motors that have been overhauled have had about a 1/8" hole drilled into each tappet bearing wall, in the block - this allows a soft steel pin (aka, a nail) to be inserted to engage with a helical slot in the tappet body, holding it still while the threaded adjuster is turned. Yes, you need to turn the crank as you adjust the valves - to set the clearances correctly, the valve must be completely closed and the tappet resting on the base circle of the cam. The I&T manual will give correct clearances as well as the setting procedure. HTH llater, llamas
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