When working with Plastigage, three precautions should be taken, Before testing, it is very important to see to it that all the oil and grease will be 'off' at the
Crankshaft and bearing surfaces, do not revolve the crankshaft while the Plastigage is in place as this would be damaging to this piece of equipment, and also while removing the Plastigage, be very careful not to harm the crankshaft or the bearing surfaces and when doing this, only use fingers or a Main and connecting rod bearings have to be checked whenever an engine is overhauled, also for reused bearings and new ones; the procedure is similar. It is advised that you start with the placement of main bearings and caps followed by cleaning all the grit and oil from the crankshaft and bearing journal. Put dowels of Plastigage across every main bearing journal and then loosely screw every main bearing cap and tighten it to recommended torque that must see the arrow on every cap pointing towards the front side of the applicable engine. When tightening is complete, for each bearing, remove the bearing cap and then compare the flattened width of the Plastigage strip with the scale on the envelope to know the bearing clearance. If the Plastigage is flattened more near to the ends than towards the middle of the width, then it can be ascertained if there is journal taper or not as per standard limit. To check for out-of-round, you have to uninstall the PlastiGage, turn the crankshaft by 90 degrees and redo the clearances checks to compare the two readings in order to determine eccentricity. For connecting rod bearing clearances, each
Piston/rod assembly is to be fitted and Plastigage used as mentioned earlier together with checking of connecting rod side clearance. If the bearings are within the tolerance limits then they may be fitted, but if they are outside then they have to be replaced with the correct one, where the upper and lower bearings have to fit together.