measuring the main bearing
clearances on a large two stroke marine diesel engine
using swedish feelers
Main bearing clearances on a 2 stroke
crosshead engine are measured using a set of retractable feelers
sometimes referred to as "Swedish feelers"
The clearance is measured at the top of
the bearing, and to obtain access, the engine is first turned so
that the crankwebs are horizontal.
By sitting on the crankweb, the Swedish
feelers can be slid down the gap between the web and the bearing.
The clearance can be measured by extending
the feelers into the gap between journal and bearing.
The feelers should be fully retracted
before attempting to remove them; if they are not, there is a chance
of breaking a feeler in the clearance gap, meaning the bearing will
have to be lifted!!
Clearance values will depend on the size of the
engine but for a 980mm bore engine (where the crankshaft diameter is
990mm) the clearance is between 0.45 and 0.75 mm with a maximum allowable
of 0.9mm. For a 500mm bore engine the allowable clearance is quoted as
being between 0.4mm and 0.58mm
Modern bearings are usually of the thinwall
type. The clearance on these bearings is non adjustable and the bearing is
changed when the clearance has reached a maximum.