update: carried out a compression test and found the following,
Bank 1;
cyl1 14 bar
cyl2 14.5 bar
cyl3 14.25 bar
cyl 4 14.5 bar
now with bank 2 cylinder 5,6,7,8 all climbed to 20bar and wanted to keep climbing (max pressure on compression tester was 20bar)
rocker cover was then removed to...