A 9 1/2 ton special delivery was signed for last Thursday, when the generator returned from Bowers. As you might guess, the refitting was the reverse of the removal, with the generator loaded first, followed by the turbocharger and the exhaust stack. Finally the roof was dropped back into place. It sounds simple but the whole process took 8 hours with the crane, mainly lining up the coupling between the generator and engine. There are 12 large fitted bolts and all the holes must line up perfectly, so this took a great deal of adjustment with the crane and persuasion with a selection of pinch bars. After four bolts were driven in, the supporting tie bars were removed, and the generator could be barred round to fit the rest.
Once all the bolts were in place, they were each tightened by Kev using his special flogging spanner and a “precision” sledge hammer. The real precision job then started – alignment of the generator to the engine crankshaft. The generator armature is supported at the far end by a roller bearing, but the inner end is bolted to the end of the crankshaft, and so half the weight is supported by the engine main bearings. It is therefore important that the position of the roller bearing is exactly in line with the crankshaft, so that the weight is evenly spread. At the same time the outer casing of the generator (with the field coils) must maintain a small but even air-gap clearance with the armature – it not being advisable for the two to make contact.
Kev fitted a DTI clock gauge to the generator fan, to check the air gap, and a Sulzer crankshaft deflection gauge between the crank webs of No8 piston. The generator casing was adjusted from side to side, at front and back, barring the engine round and checking the clocks until the changes in readings were at a minimum. Side to side adjustment of the generator is made by pulling it across the bed-plate with side bolts, and then locking into position with “bobbin” bushes that clamp the side of the generator. Fortunately the vertical deflections were almost identical, so the shims did not have to be altered for the generator height. The crankshaft deflections were reduced to just over +/- 1/1000th of an inch, side to side, which Kev declared satisfactory.
To check the armature bearing was still running true, a depth gauge was used to check the position of the rollers relative to the inner race. Finally the vertical mounting bolts were tightened, after reamering out the two middle bolts which are a transition fit into the bedplate to take any shear forces. All bolts had to be tightened evenly, barring round the engine every time to check the clearances and deflections. This whole alignment task took another day to complete.
The rest of the team made a start on rebuilding the rest of the engine, connecting up a new leather gasket between the turbocharger and the inlet box. The two halves of the sealing plates at the end of the engine were bolted back in position, having been cleaned and fitted with new gaskets. The electrical braids between the generator and underfloor busbars proved particularly troublesome, especially when it was realised that there was a mixture of imperial and metric bolts, with certain holes having been enlarged. We retired at the end of an exhausting 4 days to allow our wounds to heal before resuming the battle next Saturday.
Looking down on the coupling bolts, armature support bars still in place
Tightening up the nuts on the coupling bolts, support bars removed
Kev torque tightens the nuts for the coupling using his calibrated device
Ex works turbocharger waiting to be loaded
Turbocharger being craned into 33035
Turbocharger and exhaust stack mounted back on top of generator
Crankshaft deflection gauge mounted between webs at No8 piston
Dial indicator mounted on fan, measuring inside edge of outer casing
Checking the air gap clearances as generator is barred round
Carl reamers the vertical fitted bolt holes for the generator mounting to the bedplate
Satisfactory end to a long weekend - generator aligned and bolted down tight!