Hi Greg
This is because the timing chain tensioner generally isn't removed for just replacing the valve stem seals. If you remove all the bridges without removing the tensioner, the tension on the cam sprocket can cause the rear of the cam to come up and lead to damage to the cam or bearings. Because the procedure I outlined doesn't call for repositioning of the crankshaft during the operation, but relies solely on air pressure, you have to have a very good dependable source of air pressure. It also acknowledges that the crank could turn backwards during pressurization, which would make me feel better having the tensioner left in place (keeping the timing chain fairly tight due to the internal spring). But again I would insist on using a socket and bar to rotate the crankshaft in the normal direction about 1/2 a turn before attempting to start to ensure the tension on the chain is correct again, in case it DID move backwards.

I would recommend torquing the camshaft bearings/caps any time before the tensioner is installed. On or off car I wouldn't worry about, as long as there is no tension on the cam sprocket.

Gilly

PS another advantage to removing one rocker arm bracket at a time is this way you can more easily manage the hardware that is being removed, such as getting the brackets back over the same valves, and also those small cup shaped spacers on top of the valve stems DO come in different thicknesses (2 or 3 thicknesses, I think 2) so you want to make sure to put them back in their original places, and again doing 1 at a time makes this less prone to goof ups.