R-4360 Service History
C-97 and KC-97 Aircraft in Air National Guard Units
Submitted by John Schauer

Minneapolis-St. Paul International Airport
St. Paul, Minnesota 55111

SUBJECT: Maintenance
TO: Pilots and Flight Engineers


1. So many years have gone by since I have had the opportunity to write a letter to aircrews that I do not know if I can revive the nasty side of myself sufficiently to make an impression. As a fresh start maybe I should confine this letter to some information, which will be of interest to you if you have interest at all.

2. This message will be restricted to R4360-59B engines. Out of 17 Air National Guard bases that fly C-97Gs, we rank 16th in engine life. That really isn't news to you but I thought I would let you know things really haven't changed much. The unit that ranks first over the past year averages over 400 hours more time on its engines.

3. The average overhaul cost on one of our engines is $21,125 which includes both parts and labor. It may surprise you to learn that the Air Force is still making improvements on the R4360-59B. There have been eleven recent improvements made that I will briefly describe for you.

  1. Master rod Bearing Lubrication — deactivation of the oil diverter-segregator valve and modification of the oil tank.
  2. Master rod Bearing Improvements — reduction of silver on the bearing back to prevent flowing of the silver and buildup of high spots on the inside diameter.
  3. Front Main Bearing Lubrication — planetary magneto drive oil feed passage increased from 0.030 inch to 0.060 inch, metering oil jet to front cam removed, pressure oil skates incorporated in the planetary magneto drive gear, front main bearing removed and re-lead indium plate at each overhaul.
  4. Exhaust valve seat pinch fit increased — a slight increase in the pinch fit between the cylinder head and exhaust valve seat plus an improved technique in sizing of the seat recess.
  5. Exhaust manifold front anchoring neck replacement — incorporation of a doubler patch and installation of a new neck manufacture from AMS-347 stainless steel.
  6. Exhaust manifold outlet — a replacement flange manufactured from AMS-347 stainless steel is machine welded in place.
  7. Pushrod cover seal material — a new Fluorocarbon Rubber seal (white in appearance) is now being used.
  8. Exhaust valve guide sizing — exhaust valve guides are being honed instead of reamed to get a more accurate size.
  9. Valve tappet roller pins — because of increased engine life (?) it has been necessary to increase the silver thickness on the tappet roller pins to reduce possible failure.
  10. Cracked collector case engine mount pads — revised maintenance instruction for dynafocal mount installation which includes a higher torque setting during build-up. Just in case you run into this problem out in the system, we can now continue an engine in service with one mount cracked provided the crack has not progressed downward off the pad portion of the case. The attaching screws on the cracked mount and adjacent mounts will be removed one at a time, lubricated, reinstalled, and the screw heads will be painted with yellow paint. You would never find one anyway.
  11. Spark plugs — two new plugs have been approved for our use. They are the Champion 7P71 and the Auto-lite PL350. They are fine wire and have the same rating as the AC-281. Now all we have to do is get some.

4. There are also eight more improvements under study at this time with test engines being positioned at various bases.

  1. Increased Cylinder Wall Lubrication — Air Force has modified one R4360-59B engine to increase the oil supply to the cylinder walls in an effort to improve piston reliability. This engine was operated at 60 inch manifold pressure 2,700 RPM for 25 hours. Engine was disassembled and pistons were found in excellent condition. This engine was reassembled tested and identified as a service test engine. R4360-59B engine P514966 was shipped to Wilmington, Delware and SAAMA message SANTTA 91511, 16 Mar 66, advises activity of required reporting.
  2. Chrome Plated Piston Ring in Second Groove — During inspection of engines at teardown it was noted that in some instances the second compression ring had lost its tension. Although no incipient piston failures were found, there was evidence of increased blow-by and high ring friction. In an effort to correct this unsatisfactory condition, one R4360-59B engine P515811 has satisfactorily completed testing with chrome plated piston rings in the second compression groove in all 28 locations. This engine has been shipped to Nashville, Tennessee as a service test engine. In view of the favorable test results 10 additional engines are being built to accelerate evaluation. Activities receiving these engines will be advised.
  3. Piston Anti-Friction and Insulating Coatings — A new anti-friction coating was developed by the manufacturers Materials Development Laboratory for use on piston walls. This coating consisted of molybdenum disulfide and lead oxide in an epoxy carrier, which is impervious to oil. One single engine cylinder has completed endurance test. Additional testing is being developed. An insulating coating was applied to the dome of an R-2800 engine piston to retard the flow of heat to the piston thereby allowing the piston to retain its physical properties for longer periods. This piston has completed 19 hours running on a single cylinder engine. Presently a coated piston is being prepared with temperature measuring equipment to evaluate true effects of the dome coating.
  4. The engine manufacturer is continuing to investigate new alloys which could be used to increase service life and offer relief for troubles associated with operational environment. Pistons of a new higher strength alloy were fabricated and tested. Initial tests were conducted at high overload conditions of 67 inch manifold pressure and 2,800 RPM, ring problems usually experienced at these extreme gas pressures were encountered, but were not transmitted to the pistons. Slight dimensional modifications are being made to accommodate the piston for the improved high temperature strength properties and the differences in coefficient of expansion. Fifty-seven pistons have been delivered to five Airlines for field evaluation. (R-2800 Engines)
  5. Starter Drive Seal — Air Force engineering and the engine manufacturer were furnished seals known to be leaking. Sectioning of the parts showed in each instance that the sealing diaphragm had become brittle and fractured. After consideration and testing of several new seals, decision was made by engineering to retain the present seal and install a diaphragm of more durable material which will not deteriorate at temperatures in the vicinity of 200°F.
  6. Spinning Intake Valves — Laboratory testing has been conducted at SAAMA during the past several years to determine cause and corrective action to prevent rapid spinning of the intake valve which occurs at high power. By positive locking lower valve spring washer accelerated valve rotation was stopped in laboratory engine. To obtain service evaluation R4360-59B, P517245 and P516849 were modified and shipped as service test engines to Will Rogers APRT Okla. SAAMA message SANTTA 91519, 22 Mar 66, advises activity of required reporting.
  7. Engine Balance — During recent discussions concerning R-4360 engine reliability the question of engine balance was brought up. Activity at Savannah Georgia has requested they be furnished four known balanced engines to service evaluate. Since a number of known changes have been made in design and repair which could have changed balance to some extent, Air Force engineering and the manufacturer were requested to determine if this engine is still adequately balanced. The engine manufacturer advises that the R4360-59B engine configuration relative to 64.10-lb crankshaft balance weight and finds current parts are completely satisfactory with no design or balance modifications required. Preliminary calculations by Air Force engineering shows no changes in part configuration required. Arrangements have been made to have contractor accomplish measurement of actual weight of various configuration rotating mass to confirm calculated findings. Target date for assembly of four known balanced engines is August 1966.
  8. Test of Self-lubricating Cam Follower on R-4360 Magneto Breaker — A breaker with a self-lubricating cam follower has been developed which eliminates the lubricating felt. SAAMA is presently performing a block test (400 hours) to determine if the self-lubricating cam follower is superior to the present breaker. Upon completion of this run, it will be installed on a test block engine having a history of magneto problems and run for 150-400 hours. Target date of completion, 1 Aug 1966.

5. There were several discussion items of interest and I have picked out three which are of interest to you. The subjects are exactly as presented. I realize this is getting to be a long letter which may discourage you from reading it at all but I also think it is information you should have.

  1. The Cause and Correction of Exhaust Valve Seat Failures
    1. This discussion will include basic principles of operation of valve and seat, types of failures, procedures at overhaul, changes in engine operation techniques necessary to obtain consistent cylinder reliability. This discussion will not include in detail abnormal causes of failure such as overspeeding or overboosting the engine beyond design limits and cracked or otherwise faulty parts. Temperature will be the key word throughout the discussion. The complete story of operation is presented in order that all personnel concerned can better understand all the overlapping phases of design, operation, type of failures, manufacturing, overhaul and operational technique necessary to insure reasonable cylinder life on any Reciprocating Aircraft engine.
    2. The exhaust flame directly affects the valve, seat and cylinder; hence it is necessary to understand the effect of engine power, speed, and fuel air mixture on exhaust flame temperature before we can understand the complete operation of the valve seat. Starting at idle speed, the exhaust temperature rises rapidly with increased speeds until maximum cruise power is reached at which time the power enrichment valve starts to open which sharply reduces the actual flame temperature. Cylinder head temperature continues to increase at engine speeds above maximum cruise due to the increasing number of power impulses. Above maximum cruise the cylinder head has reached its basic maximum capacity to cool; and therefore, the amount of fuel is substantially increased as a combustion coolant to compensate for the cylinder cooling deficiency. Since use of added fuel over and beyond that normally used would reduce power excessively and since cylinders will operate satisfactorily under power at temperatures above those obtained at maximum cruise, a compromise between cylinder head temperature and power is used to give the best overall results.
    3. The exhaust valve head is exposed to combustion temperatures during the power stroke and the entire head of the valve and part of the valve stem is exposed to exhaust temperature during the entire exhaust stroke; hence the valve is exposed either partially or completely to high temperature (1,800-2,600°F) for approximately 440° of crankshaft travel. Therefore, the valve is exposed either partially or completely to extreme heat approximately 37 seconds out of each minute. The valve dissipates this heat through the valve guide and through the seat where the two faces contact.
    4. The ni-chrome steel exhaust valve seat used in Pratt & Whitney R-4360 engines is installed in the seat recess with a 0.0058-0.0073" pinch fit. This is accomplished by cutting the recess to a specific size, gaging and obtaining premeasured seat of a known size which will provide the required fit. The cylinder is then heated to around 500°F and chilling the valve seat to less than 10°F by use of dry ice. When the seat and seat recess are stabilized at room temperature, the seat is then between 0.0058-0.0073" tight. Ni-chrome R-4360 exhaust valve seat has a measured expansion rate of 0.0000045 per inch unit length for each degree Fahrenheit change. Aluminum has an average expansion rate of 0.000001234 per inch unit length for each degree Fahrenheit change. For example a 2.800" diameter valve seat and a 2.793" seat recess were elevated to 600°F; the 0.007" pinch fit is reduced to 0.0046" loose.

      VALVE SEAT 0.0000045 X 2.800 X (600°-70°) = 0.00667
      SEAT RECESS  0.000001234 X 2.793 X (600°-70°) = 0.0182

      SEAT RECESS 2.793 + 0.0182 = 2.8112
      VALVE SEAT 2.800 + 0.0066 = 2.8066
       VALVE SEAT LOOSE = 0.0046

      When the cylinder is cold (70°F) and the engine is started the seat temperature rises first and to a considerable higher temperature than the seat recess. Hence, after ½ minute of operation, the seat temperature is about 600°F and the seat recess temperature is around 200°F, the pinch fit will have changed from 0.007" to 0.0099" pinch fit. Now the compressibility of aluminum is such that a maximum pinch fit of 0.007" is about all that will be retained, as the seat recess would be compressed approximately 0.0029" and would reduce the pinch fit under these temperatures of (600°F and 200°F) back to 0.007 inch. This, in turn, would reduce the pinch fit with a cold cylinder from the original 0.007" down to about 0.0049" pinch.
    5. With the fundamentals now covered, it should be readily evident that the exhaust valve seat is retained in a hot engine by combustion heat saturated up by the valve seat itself and the valve. Take this heat away suddenly and you have a loose valve seat. The first several times a cylinder is exposed to this condition, it will probably do little damage because of a retaining lip designed into the seat specifically for this purpose. This locking device does not keep the seat tight; its only function is to retain a loose seat. Mechanical operation of the valve mechanism with a loose seat will eventually pound the seat into the cylinder head, upsetting valve clearance which in turn aggravates the pounding by the valve. This can then only result in the seat coming completely loose from the cylinder or total cylinder failure.
    6. At this point it might be said "JUST FOLLOW THE NORMAL OPERATING INSTRUCTIONS IN THE AIRCRAFT OPERATING MANUAL" and you will have reasonable cylinder reliability. But some time must be spent discussing the specific condition known to induce cylinder problems:
      1. Fast engine starts — The colder the weather the more detrimental — Keep engine RPM down until engine is warm.
      2. Operation of engine less cowling — This should be avoided, except for short period oil leak check — RPM less than 1,200, CHT 160°C MAX, 2 minutes maximum.
      3. In flight shutdowns — Not recommended, except in actual emergency.
      4. In flight power reduction — Should be gradual — Never pull power off to idle when CHT exceeds 200°C, except in emergency.
      5. Deterioration of the ignition system in service can be a major problem to cylinder life. Cylinders misfiring causes rapid cooling of the exhaust valve seat. This can result in a loose seat condition and will eventually cause seat failure. Malfunctioning engines should only be operated under emergency conditions.
      6. Propeller thrust reversing — Should only be used when necessary — Causes high cylinder head temperatures and is always followed by low power (idle operation).
      7. Engine shutdown — Must be below 180°C CHT — if this is impossible — Rotate engine several seconds with starter if possible.
      8. Cooling Hood baffles — Must be latched and in good condition — always replace or repair defective hoods.

  2. MIL-L-22851 Oil vs. MIL-L-6082 — In 1964 an investigation was conducted to determine the cause of engine problems being experienced with MIL-L-6082 oil with two percent (2%) cyclohexanone. Inspection of the general internal condition of reciprocating engines repeatedly singled an abnormal build-up of sludge, carbon, and lacquer in Air Force engines. Field replacement of nose sections, magneto spacer cases, and blower clutches were at an all time high. Erratic torque, sluggish propellers, etc. were all too frequently reported. In view of the above, an intensive investigation was conducted by SAAMA to find an improved lubricant for Air Force engines. Our findings were:
    1. An ashless dispersant oil (MIL-L-22851) was developed in co-operation with aircraft manufactures including Pratt & Whitney, Wright Aeronautical, Lycoming, and Continental Motors. All engine manufactures and FAA sanction the use of this oil.
    2. The lubrication and heat transfer capabilities of MIL-L-6082 oil and MIL-L-22851A oil are identical. The base stock oil utilized to produce MIL-L-22851A Type II oil is MIL-L-6082 Grade 1100 Oil. The only difference being the additive as depicted in paragraphs 3.2.1 through 3.2.2 of Military Specification MIL-L-22851A.
    3. Navy and Army have converted to MIL-L-22851A oil. Navy has been utilizing MIL-L-22851A oil in all their aircraft since 1961.
    4. As of January 1962, 72 commercial users world-wide, have converted to ashless dispersant type oil.
    5. Special oil qualifications tests have been conducted by SAAMA, MAAMA, AFAPL, Navy, and contractors to insure oil delivered to the Air Force meets requirements set forth in Military Specification MIL-L-22851A. Tests will be conducted to insure quality of oil does meet specification limits.
    6. SAAMA has a program in effect since mid 1964 to evaluate results of MIL-L-22851A oil. Approximately five (5) different engine models are given special teardown analysis at SAAMA each month to evaluate effects of MIL-L-22851A oil. Internal parts of engines are inspected for condition of bearings, wear points, cleanness, if oil passages are free of foreign matter, etc. Analysis of results has provided conclusive proof MIL-L-22851A oil is satisfactory for use in all Air Force reciprocating engines.

      Availability of MIL-L-22851A Oil
      MIL-L-22851A type oil is available throughout the Air Force except in USAFE and Spain. Spain and USAFE should deplete their stock of MIL-L-6082 oil by 1 Oct 1966. Rhein-Main AB has a supply MIL-L-22851A oil on hand to service aircraft from outside the theater that have converted. Aircraft that have converted and make stops at other bases in that theater can intermix (Make-up oil) MIL-L-6082 oil with MIL-L-22851A oil. However, the use of MIL-L-6082 oil as make-up oil will reduce the dispersant action of MIL-L-22851A oil, percentage wise, depending on amount added.

  3. Engine Oil System Maintenance —; Recommendations have been made to OCAMA decreasing the frequency for oil screen cleaning intervals. Upon compliance with T.O. 1C-97-627 and when the engine has operated 200 hours or more on MIL-L-22851A oil, the following inspection and maintenance requirements are recommended:
    1. Clean and inspect main oil screen each 50 hours on KC-97 A/C and each 100 hours on C-97 A/C.
    2. Drain engine sumps, oil coolers and main oil tanks each 200 hours.
    3. Under special inspections:
      1. When main oil screen is found more than 35% clogged with carbon drain engine sumps, oil coolers and main oil tank; then repeat oil screen cleaning after each flight until screen is clean.
      2. Drain main oil tank sumps when engines have not been operated for 24 hours.

6. This teardown deficiency report information along with some reports on our engines which have been sent back for depot repair during the past few months will give you some indication of what has happened to us compared to the big picture.

7 We really aren't as bad as we may look. January through March 1966 our engine life was up enough to put us in 10th place instead of 16th, and I hope it keeps improving. This has been so long that I am too tired to be nasty so it will have to wait until next time.

LtCol, MinnANG



R-4360-59B C/KC-97
PURPOSE: This report contains TDF data by primary reason for overhaul and compares the previous years data.

Reason for Overhaul Percentage
Jun-Dec 1965
Maximum Time & Directed 31.0 9.1 18.6 31.8 32.5
Master Rod Bearing Failure 13.4 30.6 22.6 12.8 10.3
Burned Piston 13.4 12.2 7.3 4.5 9.2
No Failure Found 12.0 2.0 7.2 4.7 6.1
Turbo Supercharger Failure 2.1 3.0 2.8 1.3 3.6
Collector Case Cracked. Engine Mount Pad 3.5 4.0 2.7 2.3 1.7
Overboost 1.4 1.0 2.3 3.4 3.9
Foreign Object Damage 1.4 11.2 2.2 11.2 5.1
Hydraulic Lock 1.4 2.0 1.9 3.0 2.4
Exhaust System Front Anchoring Neck Failure 2.1 1.0 1.0 1.2
Exhaust Valve Seat Loose 0.0 1.0 0.9 2.7 0.4


R-4360-59B Engines C-97 Aircraft
June — Dec 1965

Reason for Teardown Number 142 (ANG)
Engines Percent
Maximum Time 44 31.0
Master Rod Bearing Failure 19 13.4
Piston Burned 19 13.4
No Failure Found 17 12.0
Engine Mount Pad Cracked 5 3.5
Cylinder Holddown Bolts Broken 4 2.8
Cam Drive Gear Failure 4 2.8
Link Rod Failure 4 2.8
Exhaust Manifold Failure 3 2.1
Turbo Failure 3 2.1
Foreign Object Damage 2 1.4
Scored Cylinders 3 2.1
Hydraulic Lock 2 1.4
Overspeed 2 1.4
Overboost 2 1.4
Nose Case Chaffed 1 0.7
Nose Case Oil Leak 1 0.7
Tappet Roller Pin 1 0.7
Access Case Attach Studs 1 0.7
Magneto Case Cracked 1 0.7
Master Rod Broken 1 0.7
Oil Scavenge Pump Body Broken 1 0.7
Exhaust Guides Worn 1 0.7
Low Power 1 0.7


12 Month
Jan-Mar 1966
Avg Eng Life 983
Oct-Dec 1965
Avg Eng Life 950
Jul-Sep 1965
Avg Eng Life 975
Apr-Jun 1965
Avg Eng Life 958
Tulsa, Oklahoma 5 1225 1182 1291 929 1500
St. Joseph, Missouri 3 1245 1182 1272 1187 1340
Manchester, New Hampshire 4 1237 1500 1200 1077 1174
Nashville, Tennessee 2 1275 1383 1248 1167 1302
Phoenix, Arizona 13 1011 950 1138 1068 890
Will Rogers, Oklahoma 7 1160 1182 1344 1124 990
Salt Lake City, Utah 1 1287 1500 1089 1162 1398
Memphis, Tennessee 8 1149 1064 1189 1303 1041
Brooklyn, New York 15 961 1033 758 1003 1252
Philadelphia, Pennsylvania 9 1149 872 1200 1500 1025
Savannah, Georgia 10 1140 1118 1104 1262 1079
Minneapolis, Minnesota 16 875 1100 774 745 882
White Plains, New York 11 1077 1272 858 1292 888
Schenectady, New York 6 1199 1219 1310 1040 1229
Wilmington, Delaware 12 1050 950 1001 1500 750
Marietta, Georgia 14 997 1037 1085 817 1049
Van Nuys, California 17 793 696 781 825 870


12 Month
Jan-Mar 1966
Avg Eng Life 902
Oct-Dec 1965
Avg Eng Life 789
Jul-Sep 1965
Avg Eng Life 741
Apr-Jun 1965
Avg Eng Life 700
Chicago, Illinois 5 848 797 1115 748 733
Milwaukee, Wisconsin 2 1016 732 886 1500 946
Knoxville, Tennessee 1 1171 1500 1500 902 782
Dallas, Texas 3 1000 1500 1021 496 986
Wilmington, Ohio 4 870 1500 593 892 496


MAC HU-97 Base
12 Month
Jan-Mar 1966
Avg Eng Life 983
Oct-Dec 1965
Avg Eng Life 950
Jul-Sep 1965
Avg Eng Life 975
Apr-Jun 1965
Avg Eng Life 958
Wheelus 2 1030 973 1310 847 990
Hickam 1 1100 1131 1042 1033 1196
Burmuda 3 936 934 891 860 1061