47-10-33 LOCKHEED: (Was Service Note 4 of AD-763-3.) Applies to Model 49.
Difficulties have been experienced with cylinder heads turning or unscrewing slightly on certain Wright 739C18BA1 and 2 engines. This condition has occurred on older type cylinders having barrels designated as "light type" barrels. Later type cylinders have "heavy type" barrels on which this turning tendency has been eliminated. Heavy type cylinder barrels have a circumferential groove on the mounting flange to distinguish them from the light type barrels.
Following procedure shall be established for inspection and replacement as necessary of light barrel cylinders:
(a) Prior to certification or next 60 hours of operation:
(1) Mark detonation pickup bosses on light barrel cylinders with yellow paint for ready identification.
(2) Scribe front of these light barrel cylinders by marking heavy flange near bottom of cylinder head and continuing scribe line down seven barrel fins. Dark paint maybe used as background for scribe lines. Wright Aeronautical have provided a scribing tool which may be used for this purpose. The scribe line should be on front of cylinders where it can be easily seen with engines installed in airplanes.
(b) After each succeeding 35 to 60 hours of operation:
(1) Inspect scribe lines for signs of cylinder head turning.
(2) Cylinder heads which have turned 1/32 inch or more since prior inspection should have valve clearances checked and reset to normal cold clearances if necessary, provided total head turning does not exceed 1/8 inch.
(3) Cylinders on which heads have turned more than 1/8-inch total shall be replaced immediately with heavy barrel cylinders.
(c) At first engine overhaul, light barrel cylinder Nos. 1, 11, 13, 15, and 17 shall be replaced with heavy barrel cylinders. Replaced cylinders may be used in other locations provided total amount of turning has not exceeded 1/8 inch.