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Maintenance and Repairs

Renewing A Crankshaft on a Wartsila 32Bearing failure will lead to crankshaft replacement if overheating has taken place

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Replacing a crankshaft on a medium speed engine can become necessary after a bearing failure if damage to thecrankshaft 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, andoften could be reground.

Modern crankshafts for medium speed engines are manufactured from high tensile steel; for instance a 3% chromiummolybdenum nitriding steel (EN40B or BS 970 722M24). Whether these shafts are surface hardened or otherwise, thesevere overheating that can occur (above 700°C) when a bearing fails may render the crankshaft beyond repair. On a nonehardened crankshaft, bending and cracking can occur, together with localised hardening. Where the crankshaft has beensurface hardened, then annealing can occur, together with cracking.

The following photographs were taken during a crankshaft replacement on a Wartsila 32 engine. Thanks to JohnKoufopoulos 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 pumpedout. Turbocharger(s) and air cooler removed. Cylinderheads, 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 upthrough the liner bores. Bearing caps are removed, andthe crankshaft can then be lowered. Alternatively thecrankshaft can be lowered after the frame has been liftedand supported.

Holding down bolts are removed. The equipment to liftthe engine frame may have to be fabricated and loadtested. In the case shown it takes the form of two plateswith welded lifting eyes bolted onto the entablature usingthe cylinder head studs.

The engine frame is now lifted to a height which willallow the crankshaft to be removed either longitudinallyor sideways from the engine. The engine frame is landedon supports.

In this particular case the crankshaft was removedlongitudinally.

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

This view shows the crankshaft prior to fitting in theengine. Note the projecting studs for fitting thecounterweights.

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 intoposition, and the holding down bolts replaced. reassembly is basically the reverse of disassembly, with checks forcrankshaft alignment. Rechocking may be required if the alignment has been disturbed, with the engine originallymounted on resin chocks.

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

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