Maintenance and Repairs

Renewing A Crankshaft on a Wartsila 32

Bearing failure will lead to crankshaft replacement if overheating has taken place
 

Replacing a crankshaft on a medium speed engine can become necessary after a bearing failure if damage to the crankshaft journals has occurred, and regrinding of the crankshaft is not feasible. On older engines a 0.4% carbon steel (EN8 or BS970 080M40) was used for the manufacture of crankshafts. This material could withstand overheating, and often could be reground.

Modern crankshafts for medium speed engines are manufactured from high tensile steel; for instance a 3% chromium molybdenum nitriding steel (EN40B or BS 970 722M24). Whether these shafts are surface hardened or otherwise, the severe overheating that can occur (above 700C) when a bearing fails may render the crankshaft beyond repair. On a none hardened crankshaft, bending and cracking can occur, together with localised hardening. Where the crankshaft has been surface hardened, then annealing can occur, together with cracking.

The following photographs were taken during a crankshaft replacement on a Wartsila 32 engine. Thanks to John Koufopoulos for the photos.

Bearing Failure

 

In the case where an underslung crankshaft has to be replaced, the following gives a guide to the procedure.

 

The engine is isolated and drained down. Oil is pumped out. Turbocharger(s) and air cooler removed. Cylinder heads, pistons and con rods, cylinder liners removed. Timing gears and camshaft removed (to lighten engine), Output shaft disconnected and flywheel removed.

Camshaft removed 

The crankshaft is supported with strops passing up through the liner bores. Bearing caps are removed, and the crankshaft can then be lowered. Alternatively the crankshaft can be lowered after the frame has been lifted and supported.

Holding down bolts are removed. The equipment to lift the engine frame may have to be fabricated and load tested. In the case shown it takes the form of two plates with welded lifting eyes bolted onto the entablature using the cylinder head studs.

The engine frame is now lifted to a height which will allow the crankshaft to be removed either longitudinally or sideways from the  engine. The engine frame is landed on supports.

In this particular case the crankshaft was removed longitudinally.

 

This view is taken lengthways through the engine. Note the protection wrapped around the bearing cap stud threads and the bearing caps lying in the sump pan.

This view shows the crankshaft prior to fitting in the engine. Note  the projecting studs for fitting the counterweights.

Above and Below: The new crankshaft is being lifted and pulled into position. Note the Wooden blocks (below) supporting the frame.

Once the crankshaft has been lifted into position and secured with bearing caps the engine frame can be lowered back into position, and the holding down bolts replaced. reassembly is basically the reverse of disassembly, with checks for crankshaft alignment. Rechocking may be required if the alignment has been disturbed, with the engine originally mounted on resin chocks.

NEXT PAGE: RENEWING  A CRANKSHAFT ON A B&W MAN MEDIUM SPEED ENGINE.

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