BROKEN CAMSHAFT BOLTS
07th Sep 2006
After joining ship and sailing out from port, it was noticed that the Aft unit cylinder exhaust temperatures were considerably higher than the forward units.
Indicator cards were taken. It was found that all the Aft units were showing only a single curved line on the diagram- more like just the compression pressure with the fuel pumps cut out.
In port the position of the camshaft at the forward end was checked with the trammel gauge provided and was found to be fine. Since the problem was at the after half of the engine the chain drive casing at the camshaft level was opened for checking.
It was found that 50% of bolts of the Aft camshaft coupling were broken, the rest were loose, and the coupling had turned from its original position, partially damaging the serrations on the mating surfaces. Attempt was made to run the engine after bringing back the coupling to its correct position and fixing it with the unbroken bolts (it was not possible to fit new bolts in place of the broken ones.)
It did not work the camshaft turned again and smoke started belching out from the T/Cs. We put back the camshaft again in correct position and cut-out all fuel pumps and exhaust valves at the Aft end, and to reduce the load proceeded to the next port at very slow speed.
3 new cutting out devices had to be fabricated to cut-out all 5 Aft end units.
At Istanbul B & W experts attended the vessel and with the help of W/Shop the camshaft was removed, the coupling dressed up, all camshaft bearing housings were machined, aligned and fitted back with new coupling bolts.
The main cause? Cylinder block jumping, which was immunized later at the yard by proper tie rod tensioning and tightening of the stay-bolts.