When inspecting the camshaft and followers be on the lookout for scoring, pitting or scuffing of the cams or followers. In severe cases the peak of the cam may literally wear away if the hardened surface is of insufficient depth or the lubrication is insufficient. On some large medium speed engines the camshaft is in one, two or three cylinder sections, where the cams are forged integral with the shaft. In the case of damage here, then the whole section would be replaced. On large modern 2 stroke crosshead engines, the camshaft is in two cylinder sections with the cams shrunk on, and moveable by using oil under pressure to expand the cams on the shaft. In these cases, a damaged cam is usually repaired by changing a section of the camshaft, although the cam can be removed and replaced under hydraulic pressure, once the section has been removed from the engine.
On some medium speed engines the individual cams are shrunk onto the camshaft, which is in one piece. Although the cams can be expanded hydraulically in some cases, to allow for adjustment to the timing, if a cam is damaged, it is not viable to remove the whole camshaft for individual cam replacement. In this case the cam is removed by making two cuts with a grinding wheel opposite each other and then finally splitting the cam with the use of wedges. Replacement is with a two piece split cam which must be accurately positioned to maintain the correct timing.
Such a procedure is outlined below on a Sulzer ZA40 engine.
In the above photo you can see the fuel cam with the fuel pump and follower removed. The damage on the peak of the cam is clearly visible. The holes just visible in the side of the cam are for connecting the hydraulic lines when expanding the cam.
Grinding jig for removing cam
Here is the grinding jig in position. The jig is moved manually from side to side whilst grinding and the feed inwards is controlled by the handwheel. Note how the camshaft and followers are protected using rags and polythene to prevent contamination with grinding wheel debris and swarf.
The final photograph shows the new split cam in position along with a new fuel pump follower and in the process of being retimed by using marks on the camshaft and the brass jig visible to the left of the new split cam. Once the correct timing has been achieved and checked, the bolts are tightened up to the final torque settings. The bearing cap to the right of the fuel cam will also be refitted.