In-Situ Machining Solutions (UK) Ltd. have recently been involved in the refurbishment of an MAN B&W 23/30 seven cylinder auxiliary generator crankshaft. The work involved on-board machining of all seven crankpins/big end bearing journals as a result of excessive wear and ovality, gained over years of arduous operating conditions.
The initial enquiry to our technical department was made by a Greek management company who indicated that one crankpin was in need of repair. With this information, one of our engineers prepared all the necessary tooling, was mobilised and flew to meet up with the vessel in the Canary Islands, hand carrying equipment.
Once on board, our engineer set about conducting a detailed mechanical, NDT crack detection and hardness survey of the No 5 damaged crankpin, which was found to be worn and oval by 0.2mm. Fortunately no cracking or hardening of the crankpin was evident.
Since wear being much greater than anticipated, it was decided that all crankpins of this engine should be surveyed. This duly took place, it was found that all seven crankpins had worn below the original manufactures tolerances, the worst showing 0.23mm of ovality, all had to be machined undersize. No cracking or hardening of the crankpins had taken place.
With this information and urgent nature of the repair, In-Situ Machining Solutions (UK) Ltd. were instructed to provide 24hr coverage of the repair to enable this crucial work to be completed whilst the ship sailed between ports on the west coast of Africa and before it set sail across the Atlantic Ocean to South America which was imperative for the management company, ship owner and for class considerations.
Such was the wear, four of the seven crankpins were machined 1mm undersize and three 0.5mm undersize to allow the installation of new undersize shell bearings.
To have stripped the engine, removed the crankshaft and repaired it in a machine shop was not an option that could be tolerated due to the ship’s scheduling with it’s important load. Machining the crankpins on board as the ship sailed was by far the most effective and cost efficient means of rejuvenating this crankshaft.
All work was completed within a fourteen-day period, inspected and passed off by the ship’s superintendant. The management company that issued the machining contract to In-Situ Machining Solutions (UK) Ltd were extremely satisfied with the way in which the company responded and executed the repair work.