ENGINE SMOKES (BLUE SMOKE) DURING START AND/OR SHUTDOWN ONLY.

TM 9-2835-255-34

3-2. TROUBLESHOOTING - CONTINUED

d. ENGINE - CONTINUED

(4) ES-20. ENGINE SMOKES (BLUE

SMOKE) DURING START AND/OR

SHUTDOWN ONLY. OK DURING

OPERATION.

This section contains troubleshooting to locate and correct the cause(s)

of blue smoke during starting and/or shutdown (not during operation)

Many of the bearing packages in the engine are air pressurized to assist

the carbon face seals in sealing oil-wetted areas. If carbon face seals

or packings do not seal properly, leakage will not occur past the seal

if the air pressure is higher than the oil pressure in that package.

Once the air pressure becomes lower than the oil pressure, oil will leak

past the seal. During engine start, the high pressure compressor

accelerates, building air pressure for the bearing packages. During

engine shutdown, the high pressure compressor decelerates, reducing air

pressure to the bearing packages. Therefore, oil pressure in the

affected bearing package may be greater than the air pressure during the

initial stages of the start cycle and during the latter stages of

shutdown, causing oil to leak past the seal. The art on this page

provides an overview of the high pressure compressor s stem and bearing

package air pressurization. Refer to this page along with in-text art

while performing troubleshooting.

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