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How to… fit new big end and main bearings - 5

5. The nitty gritty

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Submitted by Visordown on Fri, 01/09/2017 - 14:30

How to… fit new big end and main bearings - 5

The big part is, of course, getting the entire engine out and apart to get at the crank. Once done, inspect the crank journals – any scoring, scuffs or scrapes mean you need to get it overhauled – call a professional now. If it's okay, check the bearing shells that are fitted – they often have coloured markings or stamped numbers. Refer to the service manual for guidance on your engine.

Once you have the new bearings, clean everything with brake cleaner, then assemble the bearing shells inside the conrod or main bearing mounts. Cut off a length of Plastigauge and lay it across the bearing, at 90° to the rotation (as shown above). Bolt the bearing cap on, and torque it to the right spec for the engine. Take care not to turn anything: that will mash the Plastigauge all round the bearing.

Carefully loosen the bearing halves again, then use the Plastigauge measuring sheet to work out the bearing clearance from the width of the strip. If it’s within the tolerances in the service manual, you're good to go! If not, you might need different sized bearing shells – again, the service manual will help here…

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