johnno, the valve spring provides the force that tends to close the valve, we are on the same page there. When you are checking tappet clearance, if you try hard to push the feeler gauge in on these small low-speed engines with very weak valve springs, you are likely to succeed in getting it in even if there is not enough clearance, because the valve is fairly easily lifted by compressing its tiddling little spring. It won't happen with a car engine, which has vastly stronger valve springs.
The Briggs and Stratton small engines until not very long ago, were all side valve. Mike's engine was made in 1991, and is one of the side valve range. With those engines the cam follower, or tappet, rides on the camshaft as usual, but the top of the tappet acts directly on the valve stem: there is no pushrod or rocker in the system. That is why you have to check the tappet clearance by removing the crankcase ventilation valve from the valve chest low on the cylinder/crankcase casting, so you can get access to the end of the valve stem.
I'm not clear on where we were disagreeing to start with, but that is my hopefully more detailed explanation of what I was getting at. I don't want Mike to use vigour to get the feeler gauge in there, by compressing the valve spring to do it. If your point was in connection with me saying the tappet "lifts and lowers" the valve, I agree it needs the help of the valve spring to lower it, but the spring has little hope of doing this without the cooperation of the tappet. Which one lowers the valve? Both of them do. Given enough time, gravity might even do the job of the valve spring, I suppose.
