Because if you remove all the rockers there is no tendency for the cam to turn the engine because some rocker is pushing on a cam lobe. Take all the rockers off and the engine moves easily and stays put.
It was on a 116 engine. But I also own an M103 but I have not yet changed the seals. But it is in the job jar. What type of spring compressor are you using? I had to buy a special for the 116. Maybe I could borrow yours ??
I got too many cars!! Insurance eats me alive. Dave
78 Corvette Stingray - 3k
82 242 Turbo Volvo - Manual - 270k
86 300e 5 speed manual - 210k
87 420sel - 240k
89 560sl - 78k
91 420sel - 205k
91 560sel - 85k
94 GMC Suburban - 90k
97 Harley Davidson Heritage Softail - 25k
00 GMC Silverado 1 ton 30k