Category 4

service bulletin M77-3FAA-DER Approved
11 January 1977
TO: Distributors , Dealers, Engine Overhaul Facilities, Owners and Operators
of Teledyne Continental Motors’ Aircraft Engines SUBJECT: USE OF ALTERNATE AVIATION GRADE FUELS IN ENGINES
ORIGINALLY CERTIFICATED ON 80/87, 91/96, AND 100/130 GRADE FUELS Numerous customer inquiries have been received regarding the use of alternate fuels in TCM engines.
The limited availability of 80/87 octane fuel has demanded increased utilization of higher grade fuels.
The American Society for Testing and Materials (ASTM) has recently revised ASTM D910-70, theStandard Specification for Aviation Fuels. The new specification, D910-75, re-identifies the three currentgrades of aviation fuel as Grade 80, Grade 100, and Grade 100LL (low lead). The three grades replacethose fuels commonly known as Grade 80/87 and Grade 100/130.
Although Grade 100 and 100LL have the same anti-knock qualities, they differ in the maximumallowable tetraethyl lead content.
The following table provides a comparison of the current and previous fuel specifications: The amount of tetraethyl lead in these higher grade fuels has increased the lead build up and fouling ofspark plugs along with valve erosion incidents reported on some lower compression engines.
Those TCM engines most affected include the A65, A75, C75, C85, C90, C125, C145, O200, O300 andGO300 series. The following list of replacement components, by engine series, improves engine reliability whenoperating on the higher grade alternate fuels. Refer to Service Bulletin M76-8.
The valves and valve seat inserts installed in TCM engines E-165, E-185, E-225, O-470, IO-470-J andIO-470-K series engines are compatible with higher grade fuels. These engines were originallycertificated on 80/87 octane fuel; however, field service history indicates that operation on Grade 100LLdoes not adversely affect intake or exhaust valve longevity.
Spark plug lead fouling increases when higher leaded fuels are used in engines originally certificated on80/87 octane fuel. Such fouling can be reduced by more frequent spark plug cleaning and spark plugrotation. Fine wire spark plugs that are FAA approved for use in those TCM engines listed may furtheralleviate fouling problems. In any case, the rotation of plugs every 50 hours of operation andcleaning/rotation every 100 hours is recommended. A ground run at 800 to 1000 RPM of 60 to 90seconds duration just prior to shutdown will allow temperature stabilization and burnoff of depositsaccumulated during letdown and taxiing. Mixture cutoff should be accomplished at this RPM withoutreturning to idle.
Exhaust valve sticking can result from lead salt (sulfated ash) accumulation in the lubricating oil. It isrecommended that regular 50 hour oil changes be implemented to reduce such accumulation. A few stuckexhaust valves have been reported where examination of the cylinder assembly revealed an exhaust leakbetween the exhaust elbow flange and the exhaust port face. This condition created localized cylinderhead overheating and subsequent exhaust valve and guide distress.
The exhaust system should be inspected every 100 hours and leaks corrected prior to continued engineoperational service.
The TCM Engine Operator's Manual or the Aircraft Manufacturer's Owners Manual should be consultedfor the proper leaning procedures applicable to each model engine. Leaning as specified will reducespark plug fouling.
The following chart identifies the fuels considered acceptable for use in TCM engines provided theforegoing recommendations are implemented.
+ The use of Grade 100LL is highly recommended when the specified fuel is not available; however, Grade 100 may be used for limited operation when Grade 80 or 100LL is notavailable. All TCM engines which were certificated on 91/96 octane or grade 100/130 aviation gasoline will operatesatisfactorily on Grade 100LL or military Grade 115/145. It is recommended that Grade 100LL be usedin these engines because of the reduction in combustion chamber deposits realized with the lower TELcontent.
USE OF AUTOMOTIVE FUEL IN TCM AIRCRAFT ENGINES TCM does not recommend or authorize the use of automotive fuels in any of their aircraft engines. Theengine warranty and pro rata policy will be voided if such fuels are utilized. Fuels must conform toASTM-D910 or MIL-G-5572E, if satisfactory engine service life is anticipated. Automotive fuels can contain additives that act as corrosive agents, formulate gum deposits and,therefore, increase combustion chamber deposits. Continued operation on automotive fuel can lead todetonation, pre-ignition and sticking or eroded valves.
The vapor pressure of automotive fuels exceeds that allowable for aviation fuels. This increased vaporpressure increases the tendency to vapor lock at higher altitudes. A vapor lock condition can causecomplete power loss.
The use of any fuel that does not conform to the above specifications may cause cylinder assembly, valve,piston and/or piston ring damage/failure.



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