I have been wondering about why the cam chain tensioners are supposed to be loosened when checking the valve clearance. Rotating the engine CCW is pulling the chains snug in the operating direction whether the tensioner on the take-up side is tight or loose. Valve spring pressure cannot turn the cam backwards without turning the crankshaft if the tensioner is tight or loose. If the tensioner is loose then valve spring pressure could turn the cam forward. Measuring valve clearance is supposed to be done on the heel of the cam between the acceleration ramps. Accurately locating the cam is a must. Having the cam chain loose which could allow the cam to turn forward seems counter intuitive. I checked my valves two times on the initial adjustment without loosening the chain adjusters. One was with the timing marks and the other was by opening the valve on the opposite to it's maximum lift. Both methods checked the same. I have not encountered any other engine that stated to loosen the cam chain tensioners when checking valve clearance. I have certainly not done valve adjustments on every engine made but I have done a large variety of makes, models and years. Any theories out there as to why Honda says to do this?