Volkswagen Golf Diesel 2009 Mode D'emploi page 267

Engine Mechanicals
Each drive chain has a special dark link. The dark
links are only on one side of the drive chain facing
out from the engine block. For the adjustment of the
camshaft drive, the markings on the chain sprockets
must align with the dark links of the chain.
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However, to bring the camshaft drive gears into
alignment with TDC by rotating the crankshaft
requires approximately 166 revolutions of the
crankshaft. Therefore, during repairs when the drive
chains must be removed, it is acceptable that the
technician use the dark links as a guide and make his
own markings on the sprockets.
Please refer to the appropriate repair information for
complete details.