Measuring main bearing clearances
Main bearing clearances on a 2 stroke crosshead engine are measured using a set of retractable feelers sometimes referred to as "Swedish feelers"
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| "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.
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| crankwebs |
By sitting on the crankweb, the Swedish feelers can be slid down the gap between the web and the bearing.
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| By sitting on the crankweb |
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!!
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| Measure Bearing Clearance With Swedish feelers |
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.
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