Cylinder Liner Protrusion After an In-Frame Overhaul
A tech is doing an in-frame on a wet-liner six-cylinder and replaces two liners because of cavitation pitting. The block deck is cleaned with a roloc disc. The tech measures liner protrusion with a straightedge and feeler gauge and gets 0.002, 0.003, 0.002, 0.004, 0.003, and 0.002 in across the six. The OEM spec calls for 0.002-0.005 in protrusion, measured with a dial indicator and a bar, with a maximum variation between adjacent liners of 0.001 in. The tech declares it good and assembles the engine. Two thousand miles later there is coolant in the oil and a misfire on cylinder 4.
1. Identify the measurement and assembly errors that most likely led to the failure, and explain why the straightedge/feeler method is inadequate here.
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Two problems stand out. First, the straightedge-and-feeler method cannot reliably resolve 0.001 in variation across a wet liner; the straightedge bridges high spots and the feeler drag is subjective. The spec requires a dial indicator on a rigid bar referencing the block deck, with the liner clamped and the counterbore clean and dry. Second, adjacent variation: the readings as stated swing 0.002 in between neighbors (0.004 next to 0.002), which exceeds the 0.001 in adjacent limit even if each individual number is 'in spec.' Adjacent variation is what loads the fire ring unevenly and leads to head gasket failure and coolant intrusion.
Also, roloc cleaning of the counterbore can leave a dished or polished surface and debris in the counterbore ledge; the liner must seat metal-to-metal on a clean, flat counterbore, and protrusion must be checked at multiple points around each liner, not once.
2. Cylinder 4 shows coolant in the bore and a scuffed liner. Lay out the diagnostic path to confirm root cause before the block is reworked.
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Do not simply re-ring. Steps: (1) Pressure-test the cooling system with the pan off and the head on to see where coolant enters - head gasket fire ring, injector cup, or liner seal. (2) Pull the head and inspect the fire ring witness marks on #4: uneven crush or a bright unworn arc indicates low/uneven protrusion. (3) Re-measure protrusion on all six with the dial-indicator bar, recording four points per liner, to document whether #4 is low or the neighbor is high. (4) Check the counterbore for depth, flatness, and cracks; check liner O-ring condition and that the correct shim/seal kit was used. (5) Only after the sealing path is confirmed should the counterbore be cut and shimmed to bring protrusion and adjacent variation into spec, then re-check with the head torqued in sequence. The scuff is a consequence of coolant washing the bore, not necessarily the initiating fault.