Engine Block Diagnosis and Repair
Block work is measurement
The block is where clearances and geometry decide whether a rebuild lasts. Measure each bore in two axes - parallel and perpendicular to the crankshaft - at three heights: top, middle, and bottom, using a bore gauge set with a micrometer. That yields diameter, taper, and out-of-round, and it is the largest reading, not the average, that sets the overbore. A ridge at the top of the bore means the ring travel area is worn and must be cut before the pistons come out.
Bearings are verified with a micrometer on the journal plus a bore gauge in the cleaned, torqued rod or main housing, then confirmed with Plastigage. Check journals for taper and out-of-round, crankshaft runout at the center main, and thrust clearance with a dial indicator and pry bar. Rod side clearance and bearing crush matter too: insufficient crush spins a bearing, and trapping debris behind a bearing shell guarantees a hot spot.
Traps: torque plates are required for accurate boring and honing on many blocks. Main caps are matched, numbered, and directional - mixing them destroys alignment. Bearing spread and locating tangs are functional, not decoration. After hot-tanking or magnafluxing, remove every gallery plug and core plug and brush the galleries; debris left behind returns as a spun bearing. Verify ring end gap in the actual bore, squared with a piston, not from the box.
Rule of thumb: for a typical top ring, allow about 0.004 in of end gap per inch of bore - a 4.000 in bore wants roughly 0.016 in - and always defer to the ring manufacturer's spec for the application.