Thanks to Willie Chree for contributing this story of a slipped cam on a B&W 7K90GF engine, how the engine was prepared for emergency running and how the repair was effected.
About seven years ago we were on our way back from the US Gulf to the Humber on board a large bulker of 100 000 dwt. The engine was a B&W 7 cylinder K90GF (900mm bore, 1350 stroke). We were in the Western Approaches and we were running UMS (Unmanned Machinery Space) at the time as per night orders from the Chief Engineer. I was Second Engineer and I was on the squeak (duty engineer) that night when my phone rang about 0200. I recollect it was the second mate advising me that the engine seem to slow down and there was a fair number of sparks coming from the funnel. Then off went my alarm so I had an idea something was seriously wrong.
On entering the Engine Control Room I noticed that the camshaft lub oil pressure was low and all the exhaust temperatures were abnormally high apart from cylinder number 3 which was low. I pressed the panic alarm (Note: - For those of you unfamiliar with this term, this is the engineers call alarm which is there to summon assistance; marine engineers with their inverted sense of dry sarcastic humour refer to it as the panic alarm. However it doesn't mean the engineer is panicking - not that he'll ever admit it anyway! - WM) and got lub oil pressure restored to the camshaft system. By this time the Chief Engineer and the other engine room staff were down below. We could not stop as we were approaching the separation zone so we slowed down as much as possible whilst still maintaining steerage on the vessel.
On further investigation it
was obvious what the problem was;
The C/E called the Engineer Superintendent
at home, who then gave him a B&W phone number to call to arrange parts and
"Oh ja Chief you haff a problem indeed!"
It was trial and error but it worked; The engine speed we managed was about 60 rpm and gave us a speed of 9 knots.
When we got to the Humber we carried out a full repair with the assistance of the B&W service engineer.
After removing the coupling using hydraulic jacks and removing the sealing rings the old cam was then removed. This should have been done using heat alone, but we found that the heat was not enough from the tiger torches so it was ground off with a little acetylene torch assistance This was a joint decision with B&W, the superintendent and the C/E. There was no noticeable damage to the camshaft; no tears and no sign of bluing.
In order to fit the new cam the cam must be heated either in a oven or an oil bath. Because of the logistics and the time frame it was decided to go with the latter. A large portable wash tank was filled with 500l of cyl oil. It's the cheapest and has a high flash point. A geny pyrometer was used, and the cam was slung in the bath from one of the E.R.Cranes. The operation involved checking the cam was evenly heating as when we took the damaged one off the lobe was absorbing the heat and then radiating it as the engine room was cool (April in the UK).
The service engineer from B&W was very precise with the measurements and ensured the cam bore had expanded evenly; this was done using the vessels instruments which had been properly calibrated the previous voyage. The cam was positioned on to the camshaft and allowed to shrink. The coupling was replaced in a similar manner, and the section of camshaft replaced in the engine. The timing was then checked and the engine returned to its normal running condition.