The factory service manual states to loosen the rocker shafts before replacing the timing belt. I’ve always obeyed that but can we discuss why it’s necessary? Any thoughts, opinions? It adds so much more labor to the job.
When installing the timing belt, there will probably be times when the cam timing is not correct. By loosening the rocker shafts, the valves stay closed, and any possible valve/piston conflicts can be avoided.
With practice and good methodology, the cam timings should be near perfect throughout the process, but **** does happen.
I think I did my first timing belt on a Z31 about 1991 and I've done so many since then I lost count some 20 years ago. I've never once loosened the rocker shafts to do the belt and I've never had any kind of a problem. Personally I think it's a waste of time. FYI, when doing the timing belt I always do the cam and crank seals, the water pump, T-stat, belt, and belt tensioner just to be on the safe side.
Z man of Washington
After I get the belt situated on the pulleys properly, and the tensioner set, I give the cam pulleys a little tweak in the direction necessary to get max belt tension between the pulleys, then recheck the tensioner and adjust as needed. Pulling the valve covers on that engine, especially on the left bank takes a ridiculous amount of time and it's not worth the effort. ZMOW