Main Engine starting air control valve failure

What happened

On this vessel with main engine (7L80MCE), while S/B anchored offshore, ahead and astern starting was out of order.
After anchorage, start-up tests were performed. Although the engine started up several times, the en- gine became incapable of starting. As air comes into all cylinders while running by the air, the problem was surmised to be operation failure of the starting air control valve and overhaul inspection was carried out.

Findings

1) The stop disc and the closing disc fitting part (A part) contacted and abrasion occurred in a laby- rinth formation.
2) Sticking and abrasion of the closing disc piston ring occurred and contacted a section of the casing (B part).
3) The contacting part (D part) of the distributing disc and reversing disc was abraded.
4) The contacting part (C part) of the closing disc and distributing disc was abraded.

Causes

The contacting surface (C part) of the closing disc with the distributing disc was abraded, the fitting part of the stop disc and closing disc contacted and abraded in a labyrinth formation. As a result, op- eration of the closing disc became faulty and as it was functioning in an inclined condition, it is sur- mised that it damaged the part of contact with the reversing disc.

Corrective action

As emergency repair, the following was carried out:
1) The contacting part of the distributing disc and reversing disc was grinded and adjusted.
2) Adjustment of the chain gear position.
3) Removal of the closing disc and construction of a plug on the distributing disc blow hole. Due to the above repair, the control valve will be controlled via the opening and closing of the starting ball valve. In this case, if the starting ball valve sticks in open condition, the air will not stop even if fuel operation is initiated. Therefore, it was decided to shut the intermediate valve manually in emer- gencies, and shifting was completed without incidents. Later, as indicated in Fig.3, removal of the closing disc, changing of the selector valve air line, and modification of the concerned equipment was carried out.