Jacobs Engine Service Bulletin 80 TBO 1,400 hrs. FAA Approved
Air Repair, Inc., the Jacobs Engine T.C. holder, embarked on an improvement and modernization certification program in early 2003. The goals of the program were to incorporate modern materials, improve oil consumption and drainage, and to enhance performance. These improvements required a 150 hour endurance run, 50 hours of which was at 300 h.p. with 500 degrees C.H.T., 300 barrel temp, and 210 degrees oil temp. The engine was run on Phillips 25W60 oil and 100LL fuel for the entire run. All test were satisfactorily completed with no failures to parts being tested.
The improvements are described as follows:
1. A two piece oil control ring was certified which gets its tension from a spring instead of manufactured tension. This is a modern design and significantly reduced oil consumption from a normal 2 lb per hour to 1 1b per hour in the initial test run. After seating consumption at cruise power was ½ lb per hour. This is available as Air Repair, Inc. Service Bulletin 66. Retail price $29.00 each.
2. The Pistons in #4 and #5 cylinders are identical to the other pistons with the exception of the oil control ring vent holes. These were deleted similar to Pratt and Whitney engines. The oil seepage to the lower cylinders was reduced resulting in cleaner starts. This also effectively increases the oil sump capacity slightly. This is certified under Air Repair, Inc. Service Bulletin 67. Retail price $413.00 each.
3. A modern silicone gasket material was certified for all the original asbestos type gaskets. These are certified under Air Repair, Inc. Engineering Change Notice 14. Price range $1.25 to $2.75 each.
4. The cylinder base seals were changed to red silicon type orings to improve cylinder sealing. These are certified under Air Repair, Inc. Engineering Change Notice 15. Retail price $3.00 each.
5. Silicon material was used on the rocker gaskets which provides better sealing, is reusable and requires no scrapping of old gaskets. These are certified under Air Repair, Inc. Engineering Change Notice 16. Retail price $3.00 each.
6. Bronze exhaust seats were replaced with a modern, high temp, steel alloy. No valve seat problems were encountered in the run. These seats along with valve rotators should effectively end exhaust valve problems. This new part is certified under Air Repair, Inc. Service Bulletin 68. Retail price $49.00 each.
7. The nose case was modified to use modern orings under the tappet guides and the governor oil pressure fitting. These readily available orings also give superior leak resistance to the original square rings. This is approved under Air Repair, Inc. Service Bulletin 69. Price to modify your case with parts $235.00.
8. The accessory drive housing and oil pump drawings were both changed to allow for clearance for the Jasco Alternator. Although this has commonly been done for many years it is now certified under Air Repair, Inc. Service Bulletin 70. Price to modify your parts $75.00 each.
9. The crankshaft drawing was changed due to the recalculation of balance weights with the 4276 high compression pistons used in the A2 and B2. Crankshafts now may be dynamically balanced at overhaul to reduce engine vibration. This is certified under Air Repair, Inc. Service Bulletin 72. Retail price $350.00.
10. The master rod bearing clearance was slightly reduced in an attempt to decrease the oil flow and decrease oil temperature. While there were no negatives revealed in the tests the exact benefits remain to be fully determined. This is certified under Air Repair, Inc. Service Bulletin 73.
11. All hose drawings were changed under Engineering Change Notice 22 to use modern MIL6000C type hose. This was a housekeeping issue to conform current practices to the drawings.
12. The R755-9 sump flange was reworked in accordance with Air Repair, Inc. Service Bulletin 74 on B2 engines only. This allows for a more readily available source of these parts along with use of modern oil pressure hose to the nose case.
13. Air Repair, Inc. Service Bulletin 75 incorporates a 1/8” N.P.T. drain fitting in the #4 cylinder intake pipe to drain pooled oil and prevent hydraulic lock.
14. Intake and exhaust valve guide drawings were changed to use modern alloy material and allow for the use of positive type stem seals on the intake valve. This gave dramatic results in cleaner starts and no oil leaked to #4 cylinder. This is certified under Air Repair, Inc. Service Bulletin 76. Retail price $14.00 each, Intake Guide price $25.00 and Stem Seal price $14.00 each.
15. Engineering Change Notice 29 allows for a modern garlock type seal on the mag and generation drives. Retail price $9.50 each.
16. In cooperation with Champion Aerospace, Inc. Air Repair, Inc. certified REM37BY protruding electrode spark plugs. These plugs are less prone to fouling, start better, and give a more efficient fuel burn. They were certified under Air Repair, Inc. Service Bulletin 78. Retail price $32.28 each ~ Air Repair, Inc. price $20.60 each.
17. Engineering Change Notice 31 allows for the use of modern hose clamps. This is a housekeeping issue to conform the drawings to current practices.
18. Engineering Change Notice 22 allows for the use of modern MS series stop nuts. This is a housekeeping issue to conform the drawings to current practices.
19. Plain cylinder base nuts with a pal nut were certified under Air Repair, Inc. Service Bulletin 71. These nuts allow for more uniform and consistent cylinder base torquing. Retail price $2.00 each.
20. SkytronIcs weather resistant spark plug flex conduits were certified under Engineering Change Notice 24.
21. Modern type expansion plugs for the mag and generator drive gears were certified under Air Repair, Inc. Service Bulletin 77. These replace cork plugs and soldered discs. Retail price $2.50 each.
22. A number of high performance coatings were applied to internal components. The top of the piston, valve faces and inside of the cylinder head were coated with a thermal barrier to keep the heat of combustion from soaking into the parts. This directs the heat more to producing power and keeps the parts and oil cooler.
Other parts such as valve stems, and cam rollers were coated with a dry film lubricant to reduce horse power loss due to friction and reduce wear.
Several parts were coated with a thermal dispersant to allow the oil to more efficiently cool the parts and to shed oil more quickly for better scavenging on shutdown.
In conclusion, I believe that the largest improvements are the steel seats, oil control rings, solid pistons, and intake stem seals. However when this complete list of improvements is incorporated at overhaul, the engine should give trouble free service up to T.B.O.
These improvements will be made available by engine serial number. This list of improvements has added $3,200.00 to our overhaul pricing.