measure it in place, as shown in figure 3-27. Not only does the amount of flattening measure bearing clearance, but uneven flattening also indicates a tapered or worn crankshaft journal or bearing.
Do not turn the crankshaft with the Plastigage in place.
When using feeler stock to check main bearing clearances, you should place a piece of stock of the correct size and thickness in the bearing cap after it is removed. The feeler stock should be coated lightly with oil. Then you should replace and tighten the bearing cap. Note the ease with which the crankshaft can be turned. As a word of caution, do not completely rotate the engine, which could damage the bearing. Turn it only about an inch in one direction or the other.
If the crankshaft is locked or drags noticeably after the bearing cap has been replaced and tightened, then the bearing clearance is less than the thickness of the feeler stock. If it does not tighten or drag, place an additional thickness of feeler stock on top of the first and again check the ease of crankshaft movement. Clearance normally should be about .002 inch. Be sure to check the engine manufacturer's shop manual for exact specifications.
After preparing the engine block and crankshaft for reassembly, install the upper halves of the insert bearings into the engine block. Make sure all oil passages are aligned and open (fig. 3-28). Coat the bearings with lubricating oil and lower the crankshaft into place by hand or by the use of a hoist (fig, 3-25). Install the lower bearing inserts into the main bearing caps and fit them into place on the cylinder block. Tighten the main bearing caps, using proper sequence (fig. 3-29) and torque specifications. After the main bearings have been secured, the crankshaft should rotate without drag or binding.
Crankshaft end play will become excessive if the thrust bearings are worn, producing a sharp, irregular knock. If the wear is considerable, the knock will occur each time the clutch is engaged or released; this action causes sudden endwise movement of the crankshaft. Crankshaft end play should only be a few thousandths of an inch. To measure this end play, force the crankshaft endwise as far as possible by using a pry bar, and then measure the clearance between the thrust bearing and the block with a feeler gauge.
After the crankshaft has been removed from the engine, protect the crankshaft and prevent it
Figure 3-27. - Checking bearing clearance with Plastigage.
Figure 3-28. - Align these passages with passages in the cylinder block.Continue Reading