Stripping the Cylinder Head
The Second came down early and took over the watch allowing me and my Junior to get back to the generator. We disconnected the fuel oil, lube-oil and air start piping from the defective cylinder head before removing it and getting it up to the workshop for a closer examination.
A four-stroke diesel engine cylinder head contains the inlet and exhaust valves, rocker gear, cylinder relief valve air start valve and fuel injector. We soon discovered the rocker arm for the exhaust valve was indeed seized on its shaft and, the exhaust valve stem seized into the phosphor bronze valve guide.
What a mess; where do I start? Times like this I wish I worked ashore and could call in the manufacturer team - not really, looking back this is why I served a marine fitter apprenticeship; now was the time to put it into practice.
I removed the rocker arms and shaft, sliding the inlet valve rocker off the shaft after applying a little oil; it was very slack fit on the shaft.
The bushing was badly marked, but we might get away with it, albeit with excessive clearance. The seized exhaust rocker arm took a little more time; I rattled it off with a copper hammer, being careful not to damage the shaft. This rocker arm brass bush was very badly damaged and there was no way we could use it again.
I oiled and then knocked out the seized valve stem and gave it a wee rub with emery cloth-good as new- thankfully; the valve guide looked fine on closer examination.
I laid the pushrods on the stainless steel workbench top and did a quick check; thankfully they were straight and undamaged.
We carried the obvious spares for the generators, a couple of exhaust and inlet valves and springs, cylinder liners, pistons and rings, etc; but no rocker arm bushes, valve guides or push-rods. It was my job to order generator spares as required, but as I had never used these components at maintenance overhauls, I never ordered any. However I made a note to order these and have them delivered to the ship next time in Belfast.
We also carried a couple of lengths of steel and brass round bar, for machining bits and pieces for equipment. I kept these locked in my generator spares store (a tip I learned on tankers trading in Far East), as the greasers would cut them up to sell these ashore for scrap. I was going to have to machine a new bushing for the exhaust rocker arm, and I might as well make one for the inlet valve rocker as well.
I was mighty relieved that I didn’t need to make a new valve insert as didn’t carry any phosphor bronze bar, however I would have made this from the brass bar or even mild steel, leaving plenty of stem clearance and it would have got us going again.
I told the chief the good news as we trotted off to breakfast and a few hours sleep. I had expected a bawling out for not ordering the spares but he just thanked me, gave me and the Junior a couple of cold beers from his fridge, and said he would inform head office.
I was just drifting off to sleep when the Chief came into my cabin and said Head Office wanted to know how to stop this happening on their other ships. I had already thought about this and I was going to wire the oil control valve to supply pipe in the open position. This seemed to satisfy him, and before he asked, I told him I would machine a couple of new bushes for the rocker arms. (Telling him under my breath where to go!)
He was under a lot of pressure as we had three gennys; at sea we had one running, one on standby, and one under maintenance. As we came close to port and went to standby we added another generator to the switchboard, leaving the third one on standby – as things stood we had no standby and were due in Montreal in three days time.