FIGURE 2-5. Blowby Check

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Excessive lubricating oil loss

TM-55-1905-223-24-5 Bowthruster Engine for Landing Craft Utility (LCU) NSN 1905-01-154-1191 Manual

Excessive lubricating oil sludge in the crankcase

TM 55-1905-223-24-5

Table 2-2. Troubleshooting-CONT

MALFUNCTION

TEST OR INSPECTION

CORRECTIVE ACTION

STEP 8. Check for internal leaks.

a. Measure the blowby by installing a plug in the crankcase breather vent (FIGURE 2-5).

FIGURE 2-5. Blowby Check.

b. Remove the oil filler cap and replace with blowby checking tool. Connect the blowby checking

tool to a manometer. Run engine at 1500 RPM.

NOTE

Excessive blowby is indicated by a manometer reading over 12.0 in. H2O (305 cm

H2O) for an engine, with less than 3,600 hours and a manometer reading over

18.0 in. H2O (460 cm H2O) for an engine with more than 3,600 hours. Excessive

blowby indicates an internal leak. Normally internal leaks are caused by leaking

intake valve guides, piston rings not seating properly, worn or broken piston rings,

worn piston ring grooves, and scored or damaged cylinder liners. Refer to Table 3-

1, Direct Support Troubleshooting, and Table 4-1, General Support

Troubleshooting.

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