On an S50/S52 rebuild the timing truth is the cam alignment blocks, not whether a sprocket touches its stops — so the fraction of a millimetre you're chasing is a red herring.
- Lock the crank at TDC on cylinder 1 and seat the flat blocks on the machined pads at the back of both cams
- When those blocks drop in flush with the crank still at TDC, the cams are timed
The single VANOS acts on the intake cam only — the exhaust cam rides the main timing chain, and its sprocket bolts on through slotted holes purely so you can dial the exhaust cam until its block seats. So the "mechanical stops" you feel there are just the ends of that slot's travel, not a timing target — don't force the sprocket to reach them.
- Set the exhaust sprocket so its block seats cleanly at TDC, leaving the sprocket bolts snug rather than fully torqued
- Fit the VANOS: its helical splines pull the intake cam into full engagement, which is why the intake side only shows its complete range once the unit is on
- Verify by cycling the VANOS through its travel and confirming both blocks still seat flush at TDC afterwards — if one no longer drops in, you're a tooth off, far cheaper to find now than after it fires
Torque everything down only once both blocks seat cleanly with the VANOS installed. VANOS Diagnosis Timing Chain Belt