If the gear steps have been chrome-plated to remove defects, grind them to size in accordance with Figure
9-40. Be sure to maintain the fillet area radii at 0.270 to 0.230 inch (6.88 to 5.84 mm).
Check the fillet radii of all main bearing journals and gear step areas in accordance with step (21), above.
Using scleroscope hardness tester ST-1196, test the journal hardness in accordance with step d, above. If
any journal tests below 40 Rockwell, and journals have been turned to the maximum undersize, replace
Grinder bum causes softening of the metal from overheating during the grinding process.
Rehardening damage causes hard spots from overheating, combined with the quenching
action of the grinding coolant. This type of damage Is most likely to occur In the fillet area
when the grinding wheel Is traversed or bumped Into the bossing wall of the journal. Grinder
bum and rehardening are usually only shallow surface defects, but form stress risers which
will lead to breakage of the crankshaft within a relatively short period of operation. Severe
grinder bum may be visible In the form of brown or darkened spots or streaks (usually In the
fillet or bossing wall area), and sometimes can be seen Immediately after the grinding
operation. Lack of visible discoloration, however, Is not proof of freedom from grinder burn
damage. The discoloration may have been removed during spark-out or can easily be
polished away. Frequently, this damage will be Invisible and can be detected only after an
etch check. The crankshaft shall be etch checked after regrinding to ensure that It Is free of
grinder bum or rehardening damage.
(44) Conduct an etch check in each fillet area as follows: (a) Thoroughly dean the journals to remove oil and
Acids are highly toxic to the skin, eyes, and respiratory tract. Skin, eye, and respiratory
protection Is required. Keep sodium bicarbonate solution at hand to neutralize spills.
Swab each fillet and side wall generously with a 4 percent solution of nitric acid O-N-350 in water.
Apply the solution generously, using chemical tongs and a large ball of cotton. Continue to swab
with vigorous scrubbing motions until the treated surface turns very dark, gray, or black.
Acetone Is highly flammable and mildly toxic to the skin, eyes, and respiratory tract Use In an
adequately ventilated area. Skin, eye, and respiratory protection Is required to prevent Injury
Compressed air used for cleaning or drying can create airborne particles that may enter the
eyes. Pressure shall not exceed 30 psi (207 kPa). Wearing of goggles Is required to avoid
Injury to personnel.
Rinse with hot water and blow dry. Then swab with acetone O-A-51 and dean cotton swabs and blow
Etch for15 seconds to 1 minute with a solution of hydrochloric acid (2 percent hydrochloric acid O-H-
765 in acetone O-A-51). Use dean cotton swabs for this etch.
Rinse with hot water, then swab with acetone and blow dry with compressed air.