The cam is coming to a stop because the valves are touching the pistons.

I had a similar problem with my 740 because I made a mistake taking it apart and got then engine badly out of time. To get it back in time, I noted the position of the crankshaft and then rotated it a little at a time by hand and then turning the cams a little at a time until I got everything lined up. It was tedious, but worked.

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2002 X5 4.6is - Imola Red/Black (Sold)
2001 740i M Sport - Anthrazit Metallic/Black (Sold)
1998 M3/4/5 - Technoviolet/Dove (Sold)
2003 Z4 3.0i Sport - Sterlinggrau Metallic/Black (Sold)
2009 Mini JCW (The Wife's)
2015 i3 REx - Arravani Gray/Tera World (Daily Driver)