SL2022-729/AGC Preventive grinding of exhaust valve seats

Exhaust valve spindles with a bottom burn-off rate resulting in a spindle life exceeding 16,000 hrs. or 24,000 hrs., depending on whether the engine bore size is smaller or larger than 60-cm bore, will need preventive spindle seat grinding to mitigate the risk of dent mark formation, eventually resulting in seat blow-by.

Spindle seat overhaul requirement
Piston bore < 60: 16,000 hours ± 2,000 hours
Piston bore ≥ 60: 24,000 hours ± 3,000 hours
– Grind the spindle seat until the size of the dent mark is smaller than 2 mm in diameter.
– Connecting dent marks must be treated as one mark.
– Grind as little as possible in order to obtain the max. dent mark size of Ø2 mm.
– Start by grinding in steps of up to 0.2 mm in accordance with the grinding machine manual and continue if necessary.
– Preventive grinding should not exceed 0.5 mm depth.

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