Fitting The Big-Ends

Fitting The Big-Ends

Fitting the big end cap

The use of nutlock

Tensioning the big end nuts

Checking side clearance


Fitting the big-ends…… Ensure the conrod tunnels are dry and clean. Mount the conrod bearing shells ensuring the uppers are fitted to the rods and the lowers to the caps. Oil the big-end cap bearing . Check the big end cap is fitted the right way around and tension the big-ends to the correct specifications. Once tensioned, DON’T ROTATE THE ENGINE BEFORE CHECKING that the rod has the correct side clearance. It is very important that side clearance is checked in the correct manner as this is a multi-purpose test. The correct method is simply to move the rod side-ways across the journal. What you are checking when doing this test is more complex than it first appears. Firstly you are checking minimum vertical oil clearance, secondly you are checking rod alignment, thirdly you are checking if you damaged the journal while fitting the piston down the bores and finally you are checking the conrod side clearance……If the rod is hard to move sideways at first, but after a small tap it seems to free up and eventually freely moves back and forth, don’t turn the engine over as most probably the journal has a ding or burr. Once you tapped the rod sideways the burr gouged out the soft bearing material and now it moves freely from side to side. If you were to turn the engine over the same burr would gouge a mark deep into the new bearings…… Remove the cap. Push the rod back up the bore far enough to be able to repair the shaft and check the bearing. Be very careful not to contaminate the engine with abrasive grit if linishing tape is used. It is better to remove and repair the shaft out of the engine. Re-fit and re-check…… For all of those four items to be correct the rod should FREELY RATTLE BACK AND FORTH ACROSS THE JOURNAL ON THE FIRST ATTEMPT. IF OK ROTATE THE ENGINE ONE REVOLUTION CHECKING THE DRAG. WHEN ALL PISTONS ARE FITTED THE ENGINE MUST TURN FREELY. IF YOU ROTATE THE ENGINE AFTER EVERY PISTON IS FITTED ANY PROBLEMS WILL BE EASILY IDENTIFIED TO THAT CYLINDER.

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