ASTM D909-22

This document is not an ASTM standard and is intended only to provide the user of an ASTM standard an indication of what changes have been made to the previous version. Because
it may not be technically possible to adequately depict all changes accurately, ASTM recommends that users consult prior editions as appropriate. In all cases only the current version
of the standard as published by ASTM is to be considered the official document.
Designation: D909 − 21 D909 − 22 Method 6012.6—Federal Test
Method Standard No. 791b
Standard Test Method for
Supercharge Rating of Spark-Ignition Aviation Gasoline
This standard is issued under the fixed designation D909; the number immediately following the designation indicates the year of
original adoption or, in the case of revision, the year of last revision. A number in parentheses indicates the year of last reapproval. A
superscript epsilon (´) indicates an editorial change since the last revision or reapproval.
This standard has been approved for use by agencies of the U.S. Department of Defense.
1. Scope*
1.1 This laboratory test method covers the quantitative determination of supercharge ratings of spark-ignition aviation gasoline.
The sample fuel is tested using a standardized single cylinder, four-stroke cycle, indirect injected, liquid cooled, CFR engine run
in accordance with a defined set of operating conditions.
1.2 The supercharge rating is calculated by linear interpolation of the knock limited power of the sample compared to the knock
limited power of bracketing reference fuel blends.
1.3 The rating scale covers the range from 85 octane number to Isooctane + 6.0 mL TEL ⁄U.S. gal.
1.4 The values of operating conditions are stated in SI units and are considered standard. The values in parentheses are the
historical inch-pound units. The standardized CFR engine measurements and reference fuel concentrations continue to be in
historical units.
1.5 This standard does not purport to address all of the safety concerns, if any, associated with its use. It is the responsibility
of the user of this standard to establish appropriate safety, health, and environmental practices and determine the applicability of
regulatory limitations prior to use. Specific precautionary statements are given in Annex A1.
1.6 This international standard was developed in accordance with internationally recognized principles on standardization
established in the Decision on Principles for the Development of International Standards, Guides and Recommendations issued
by the World Trade Organization Technical Barriers to Trade (TBT) Committee.
2. Referenced Documents
2.1 ASTM Standards:
D1193 Specification for Reagent Water
D2268 Test Method for Analysis of High-Purity n-Heptane and Isooctane by Capillary Gas Chromatography
D3237 Test Method for Lead in Gasoline by Atomic Absorption Spectroscopy
D3341 Test Method for Lead in Gasoline—Iodine Monochloride Method
D4057 Practice for Manual Sampling of Petroleum and Petroleum Products
D4175 Terminology Relating to Petroleum Products, Liquid Fuels, and Lubricants
This test method is under the jurisdiction of ASTM Committee D02 on Petroleum Products, Liquid Fuels, and Lubricants and is the direct responsibility of Subcommittee
D02.01 on Combustion Characteristics.
Current edition approved Dec. 1, 2021May 1, 2022. Published December 2021May 2022. Originally approved in 1958. Last previous edition approved in 20182021 as
ɛ1
D909 – 18D909 – 21. . DOI: 10.1520/D0909-21.10.1520/D0909-22.
For referenced ASTM standards, visit the ASTM website, www.astm.org, or contact ASTM Customer Service at service@astm.org. For Annual Book of ASTM Standards
volume information, refer to the standard’s Document Summary page on the ASTM website.
*A Summary of Changes section appears at the end of this standard
Copyright © ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959. United States
D909 − 22
D5059 Test Methods for Lead and Manganese in Gasoline by X-Ray Fluorescence Spectroscopy
D6299 Practice for Applying Statistical Quality Assurance and Control Charting Techniques to Evaluate Analytical Measure-
ment System Performance
E344 Terminology Relating to Thermometry and Hydrometry
E456 Terminology Relating to Quality and Statistics
2.2 CFR Engine Manuals:
CFR F-4 Form 846 Supercharge Method Aviation Gasoline Rating Unit Installation Manual
CFR F-4 Form 893 Supercharge Method Aviation Gasoline Rating Unit Operation & Maintenance
2.3 Energy Institute Standard:
IP 224/02 Determination of Low Lead Content of Light Petroleum Distillates by Dithizone Extraction and Colorimetric Method
2.4 ASTM Adjuncts:
Rating Data Sheet
Reference Fuel Framework Graphs
3. Terminology
3.1 Definitions:
3.1.1 accepted reference value, n—a value that serves as an agreed-upon reference for comparison, and which is derived as: (1)
a theoretical or established value, based on scientific principles, or (2) an assigned or certified value, based on experimental work
of some national or international organization, or (3) a consensus or certified value, based on collaborative experimental work
under the auspices of a scientific or engineering group. E456
3.1.1.1 Discussion—
In the context of this test method, accepted reference value is understood to apply to the supercharge and octane number ratings
of specific reference materials determined empirically under reproducibility conditions by the National Exchange Group or another
recognized exchange testing organization.
3.1.2 brake mean effective pressure, n—for spark-ignition engines, the measure of engine power at the output shaft as typically
measured by an absorption dynamometer or brake.
3.1.3 check fuel, n—for quality control testing, a spark-ignition engine fuel having a supercharge rating accepted reference value
determined in accordance with Practice D6299 requirements for check standards using interlaboratory testing.
3.1.4 firing, n—for the CFR engine, operation of the CFR engine with fuel and ignition.
3.1.5 friction mean effective pressure, n—for spark-ignition engines, the measure of the difference between IMEP and BMEP or
power absorbed in mechanical friction and any auxiliaries.
3.1.6 fuel-air ratio, n—mass ratio of fuel to air in the mixture delivered to the combustion chamber.
3.1.7 indicated mean effective pressure, n—for spark-ignition engines, the measure of engine power developed in the engine
cylinder or combustion chamber.
3.1.8 intake manifold pressure, n—for supercharged engines, the positive pressure in the intake manifold.
3.1.9 knock-limited power curve, n—for supercharge method knock rating, the non-linear standard knock intensity characteristic
of a primary reference fuel blend or a sample fuel, expressed as indicated mean effective pressures, over the range of fuel-air ratios
from approximately 0.08 to approximately 0.12.
3.1.10 mean effective pressure, n—for internal combustion engines, the steady-state pressure which, if applied to the piston during
the expansion stroke, is a function of the measured power.
Available from CFR Engines, Inc., N8 W22577, Johnson Dr., Pewaukee, WI 53186.
Available from Energy Institute, 61 New Cavendish St., London, W1G 7AR, U.K., http://www.energyinst.org.
See The Internal-Combustion Engine by Taylor and Taylor, International Textbook Company, Scranton, PA.
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3.1.11 octane number, n—for spark-ignition engine fuel, any one of several numerical indicators of resistance to knock obtained
by comparison with reference fuels in standardized engine or vehicle tests. D4175
3.1.12 power curve, n—for supercharge method knock rating, the characteristic power output, expressed as indicated mean
effective pressure, over a range of fuel-air ratios from approximately 0.08 to approximately 0.12, when a supercharge test engine
is operated on isooctane plus 6 mlmL of tetraethyllead per U.S. gallon under standard conditions at a constant intake manifold
pressure of 40 in. of Hg (134.3 kPa) absolute.
3.1.13 quality control (QC) sample, n—for use in quality assurance programs to determine and monitor the precision and stability
of a measurement system, a stable and homogeneous material having physical or chemical properties, or both, similar to those of
typical samples tested by the analytical measurement system. The material is properly stored to ensure sample integrity, and is
available in sufficient quantity for repeated, long-term testing. D6299
3.1.14 reference fuel framework, n—for supercharge method knock rating, the graphic representation of the knock-limited power
curves for the specified primary reference fuel blends of isooctane + n-heptane and isooctane + TEL (mL/U.S. gal) that defines
the expected indicated mean effective pressure versus fuel-air ratio characteristics for supercharge test engines operating properly
under standardized conditions.
3.1.15 repeatability conditions, n—conditions where independent test results are obtained with the same method on identical test
items in the same laboratory by the same operator using the same equipment within short intervals of time. E456
3.1.15.1 Discussion—
In the context of this method, a short time interval is understood to be the time for two back-to-back ratings because of the length
of time required for each rating.
3.1.16 reproducibility conditions, n—conditions where test results are obtained with the same method on identical test items in
different laboratories with different operators using different equipment. E456
3.1.17 standard knock intensity, n—for supercharge method knock testing, trace or light knock as determined by ear.
3.1.17.1 Discussion—
Light knock intensity is a level definitely above the commonly defined least audible “trace knock;” it is the softest knock that the
operator can definitely and repeatedly recognize by ear although it may not be audible on every combustion cycle (intermittent
knock). The variations in knock intensity can occasionally include loud knocks and very light knocks. These variations can also
change with mixture ratio; the steadiest knock typically occurring in the vicinity of 0.09 fuel-air ratio.
3.1.18 supercharge performance number, n—a numerical value arbitrarily assigned to the supercharge ratings above 100 ON.
3.1.19 supercharge rating, n—the numerical rating of the knock resistance of a fuel obtained by comparison of its knock-limited
power with that of primary reference fuel blends when both are tested in a standard CFR engine operating under the conditions
specified in this test method.
3.2 Definitions of Terms Specific to This Standard:
3.2.1 primary reference fuels, n—for knock testing, volumetrically proportioned mixtures of isooctane with n-heptane, or blends
of tetraethyllead in isooctane which define the supercharge rating scale.
3.3 Abbreviations:
3.3.1 ARV—accepted reference value
3.3.2 ABDC—after bottom dead center
3.3.3 ATDC—after top dead center
3.3.4 BBDC—before bottom dead center
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3.3.5 BMEP—break mean effective pressure
3.3.6 BTDC—before top dead center
3.3.7 C.R.—compression ratio
3.3.8 FMEP—friction mean effective pressure
3.3.9 IAT—intake air temperature
3.3.10 IMEP—indicated mean effective pressure
3.3.11 NEG—National Exchange Group
3.3.12 O.N.—octane number
3.3.13 PN—performance number
3.3.14 PRF—primary reference fuel
3.3.15 RTD—resistance thermometer device (Terminology E344) platinum type
3.3.16 TDC—top dead center
3.3.17 TEL—tetraethyllead
3.3.18 UV—ultra violet
4. Summary of Test Method
4.1 The supercharge method rating of a fuel is determined by comparing the knock-limited power of the sample to those for
bracketing blends of reference fuels under standard operating conditions. Testing is performed at fixed compression ratio by
varying the intake manifold pressure and fuel flow rate, and measuring IMEP at a minimum of six points to define the mixture
response curves, IMEP versus fuel-air ratio, for the sample and reference fuels. The knock-limited power for the sample is
bracketed between those for two adjacent reference fuels, and the rating for the sample is calculated by interpolation of the IMEP
at the fuel-air ratio which produces maximum power (IMEP) for the lower bracketing reference fuel.
5. Significance and Use
5.1 Supercharge method ratings can provide an indication of the rich-mixture antiknock performance of aviation gasoline in
aviation piston engines.
5.2 Supercharge method ratings are used by petroleum refiners and marketers and in commerce as a primary specification
measurement to ensure proper matching of fuel antiknock quality and engine requirement.
5.3 Supercharge method ratings may be used by aviation engine and aircraft manufacturers as a specification measurement related
to matching of fuels and engines.
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FIG. 1 Supercharge Unit
6. Interferences
6.1 Precaution—Avoid exposure of sample fuels to sunlight or fluorescent lamp UV emissions to minimize induced chemical
reactions that can affect octane number ratings.
6.1.1 Exposure of these fuels to UV wavelengths shorter than 550 nm for a short period of time can significantly affect octane
number ratings.
6.2 Electrical power subject to transient voltage or frequency surges or distortion can alter CFR engine operating conditions or
knock measuring instrumentation performance and thus affect the supercharge rating obtained for sample fuels.
7. Apparatus
7.1 Engine Equipment —This test method uses a single cylinder, CFR engine that consists of standard components as follows:
crankcase, a cylinder/clamping sleeve, a thermal siphon recirculating jacket coolant system, an intake air system with controlled
temperature and pressure equipment, electrical controls, and a suitable exhaust pipe. The engine flywheel is connected to a special
electric dynamometer utilized to both start the engine and as a means to absorb power at constant speed when combustion is
occurring (engine firing). See Fig. 1 and Table 1.
7.1.1 The CFR Engines, Inc. designation for the apparatus required for this test method is Model CFR F-4 Supercharge Method
Octane Rating Unit.
Supporting data have been filed at ASTM International Headquarters and may be obtained by requesting Research Report RR:D02-1502. Contact ASTM Customer
Service at service@astm.org.
The sole source of supply of the engine equipment and instrumentation known to the committee at this time is CFR Engines, Inc., N8 W22577, Johnson Dr., Pewaukee,
WI 53186. If you are aware of alternative suppliers, please provide this information to ASTM International Headquarters. Your comments will receive careful consideration
at a meeting of the responsible technical committee, which you may attend.
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TABLE 1 General Rating Unit Characteristics and Information
Cylinder 7.0 : 1 C.R. - Fixed
Standard Bore, in. 3.25
Stroke, in. 4.5
Displacement, cu in. 37.33
Valve gear enclosed
Rocker arm bushing needle
Intake valve plain with rotator
Exhaust valve sodium cooled with rotator
Valve felts both valves
Piston aluminum
Compression rings:
Type keystone
Number required 3
Oil control rings:
Type keystone
Number required 2
Crankcase CFR48
Rotating balance weights CFR48, non-leaded
version
Camshaft, deg overlap 30
Ignition capacitor discharge
Spark plug
Type Aviation
Gasket solid Copper
Humidity control compressed air
Fuel system manifold injection
Pump timing inlet port closes at 50 ± 5
deg ATDC,
intake stroke
Injection pump:
Plunger diameter, mm 8
Lift at port closure, in. 0.100 to 0.116
Injector Pintle type
Injector line
Bore, in. 1/8
Length, in. 20 ± 2
7.2 Auxiliary Equipment—A number of components and devices have been developed to integrate the basic engine equipment into
complete laboratory measurement system.
8. Reference Materials
8.1 Cylinder Jacket Coolant—Ethylene Glycol shall be used in the cylinder jacket with the required amount of water to obtain a
boiling temperature of 191 °C 6 3 °C (375 °F 6 5 °F). (Warning—Ethylene glycol based antifreeze is poisonous and may be
harmful or fatal if inhaled or swallowed. See Annex A1.)
8.1.1 Water shall be understood to mean reagent water conforming to Type IV of Specification D1193.
8.2 Engine Crankcase Lubricating Oil—An SAE 50 viscosity grade oil meeting the current API service classification for
spark-ignition engines shall be used. It shall contain a detergent additive and have a kinematic viscosity of 16.77 mm /s to
25.0 mm /s (cSt) at 100 °C (212 °F) and a viscosity index of not less than 85. Oils containing viscosity index improvers shall not
be used. Multigraded oils shall not be used. (Warning—Lubricating oil is combustible and its vapor is harmful. See Annex A1.)
8.3 PRF, isooctane (2,2,4-trimethylpentane) and n-heptane meeting the specifications in Table 2. (Warning—Primary reference
fuel is flammable and its vapors are harmful. Vapors may cause flash fire. See Annex A1.)
8.4 Tetraethyllead concentrated antiknock mixture (aviation mix) containing not less than 61.0 % by weight of tetraethyllead and
sufficient ethylene dibromide to provide two bromine atoms per atom of lead. The balance of the antiknock mixture shall be a
suitable oxidation inhibitor, an oil-soluble dye to provide a distinctive color for identification, and kerosene.
8.4.1 Temperature Corrections—If the temperature of the fuel is below that of the TEL, the quantity of the TEL is increased and
vice versa as calculated by the coefficient of expansion, obtained from the supplier, of concentrated TEL.
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TABLE 2 Specifications for ASTM Knock Test Reference Fuels
ASTM Isooctane ASTM n-Heptane Test Method
Isooctane, % not less than 99.75 not greater than 0.10 ASTM D2268
n-Heptane, % not greater than 0.10 not less than 99.75 ASTM D2268
Lead Content, not greater than 0.002 not greater than 0.002 IP 224/02
g/gal
8.4.2 Analysis for TEL—It is recommended that each blend of fuel, particularly drum blends, be analyzed for lead content in
accordance with standard test methods (see Test Methods D3237, D3341, and D5059.)
8.5 Isooctane+6.0 mL TEL—a mixture of isooctane and aviation mix tetraethyllead that contains 6.00 mL 6 0.05 mL of
tetraethyllead per U.S. gallon (1.68 g 6 0.014 g of elemental lead per litre) which may be blended with isooctane to prepare
reference fuel blends.
8.5.1 Blend ratios for diluting isooctane+6.0 mL TEL with isooctane to prepare the reference fuel compositions that are employed
in this test method are shown in Table 3.
9. Sampling
9.1 Collect samples in accordance with Practice D4057.
9.2 Protection from Light—Collect and store sample fuels in an opaque container, such as a dark brown glass bottle, metal can,
or a minimally reactive plastic container to minimize exposure to UV emissions from sources such as sunlight or fluorescent lamps.
10. Basic Engine and Instrumentation Settings and Standard Operating Conditions
10.1 Installation of Engine Equipment and Instrumentation—Installation of the engine and instrumentation requires placement of
the engine on a suitable foundation and hook-up of all utilities. Engineering and technical support for this function is required, and
the user shall be responsible to comply with all local and national codes and installation requirements.
10.1.1 Proper operation of the CFR engine requires assembly of a number of engine components and adjustment of a series of
engine variables to prescribed specifications. Some of these settings are established by component specifications, others are
established at the time of engine assembly or after overhaul, and still others are engine running conditions that must be observed
or determined by the operator during the testing process.
10.2 Conditions Based on Component Specifications:
10.2.1 Engine Speed, 1800 r ⁄min 6 45 r ⁄min, under both firing and non-firing conditions. The maximum variation throughout a
test shall not exceed 45 r ⁄min, exclusive of friction measurement.
10.2.2 Compression Ratio, 7.0 to 1, fixed by adjustment of the clearance volume to 108 mL 6 0.5 mL on cylinders of standard
bore by the bench tilt procedure.
10.2.3 Indexing Flywheel to TDC—With the piston at the highest point of travel in the cylinder, set the flywheel pointer mark in
alignment with the 0° mark on the flywheel in accordance with the instructions of the manufacturer.
10.2.4 Valve Timing—The engine uses a four-stroke cycle with two crankshaft revolutions for each complete combustion cycle.
The two critical valve events are those that occur near TDC; intake valve opening and exhaust valve closing.
10.2.4.1 Intake valve opening shall occur at 15.0° 6 2.5° BTDC with closing at 50° ABDC on one revolution of the crankshaft
and flywheel.
10.2.4.2 Exhaust valve opening shall occur 50° BBDC on the second revolution of the crankshaft and flywheel, with closing at
15.0° 6 2.5° ATDC on the next revolution of the crankshaft and flywheel.
D909 − 22
TABLE 3 Blends of Isooctane+6.0 mL TEL per U.S. Gallon
mL Isooctane + mL Isooctane mL TEL per
6.0 mL TEL per U.S. gallon
U.S. gallon
0 4800 0.00
400 4400 0.50
1000 3800 1.25
1600 3200 2.00
2400 2400 3.00
3200 1600 4.00
4800 0 6.00
10.2.5 Valve Lift—Intake and exhaust cam lobe contours, while different in shape, shall have a contour rise of 8.00 mm to 8.25 mm
(0.315 in. to 0.325 in.) from the base circle to the top of the lobe.
10.3 Assembly Settings and Operating Conditions:
10.3.1 Spark Advance, constant, 45°.
10.3.2 Spark-Plug Gap, 0.51 mm 6 0.13 mm (0.020 in. 6 0.003 in.).
10.3.3 Ignition Settings:
10.3.3.1 Breakerless ignition system basic setting for transducer to rotor (vane) gap is 0.08 mm to 0.13 mm (0.003 in. to 0.005 in.).
10.3.4 Valve Clearances, 0.20 mm 6 0.03 mm (0.008 in. 6 0.001 in.) for the intake, 0.25 mm 6 0.03 mm (0.010 in. 6 0.001 in.)
for the exhaust, measured with the engine hot and running at equilibrium under standard operating conditions on a reference fuel
of 100 octane number at the fuel-air ratio for maximum power and an absolute manifold pressure of 101.6 kPa (30 in. Hg).
10.3.5 Oil Pressure, 0.41 MPa 6 0.03 MPa (60 psi 6 5 psi) gage in the oil gallery leading to the crankshaft bearings.
10.3.6 Oil Temperature, 74 °C 6 3 °C (165 °F 6 5 °F) at the entrance to the oil gallery.
10.3.6.1 Engine Crankcase Lubricating Oil Level:
(1) Engine Stopped and Cold—Oil added to the crankcase so that the level is near the top of the sight glass will typically
provide the controlling engine running and hot operating level.
(2) Engine Running and Hot—Oil level shall be approximately mid-position in the crankcase oil sight glass.
10.3.7 Coolant Temperature, 191 °C 6 3 °C (375 °F 6 5 °F) in the top of the coolant return line from the condenser to the
cylinder.
10.3.8 Fuel Pump Pressure, 0.10 MPa 6 0.01 MPa (15 psi 6 2 psi) in the gallery.
10.3.9 Fuel Injector Opening Pressure, 8.2 MPa 6 0.69 MPa (1200 psi 6 100 psi) for Bosch nozzle; 9.9 MPa 6 0.34 MPa
(1450 psi 6 50 psi) for Ex-Cell-O nozzle.
10.3.10 Fuel Injector Timing—The pump plunger must close the fuel-inlet port at 50° 6 5° ATDC on the intake stroke.
10.3.11 Air Pressure, 0.37 MPa 6 0.003 MPa (54.4 psi 6 0.5 psi) absolute at the upstream flange tap of the air flow meter.
10.3.12 Air Temperatures, 52 °C 6 3 °C (125 °F 6 5 °F) in the downstream leg of the air-flow meter and 107 °C 6 3 °C
(225 °F 6 5 °F) in the intake manifold surge tank.
10.3.13 Intake Air Humidity, 0.00997 kg of water/kg (max) (70 grains of water/lb) of dry air.
10.3.14 Standard Knock Intensity, light knock as determined by ear. In determining the light knock point, it is advisable to adjust
first to a fairly heavy knock by varying either the manifold pressure or the fuel flow, return to knock-free operation, and finally
D909 − 22
adjust to the light-knock conditions. Light knock intensity is a level definitely above the commonly defined least audible “trace
knock;” it is the least knock that the operator can definitely and repeatedly recognize by ear.
10.3.15 Satisfactory Engine Condition—The engine should cease firing instantly when the ignition is turned off. If it does not,
operating conditions are unsatisfactory. Examine the engine for defects, particularly for combustion chamber and spark plug
deposits, and remedy such conditions before rating fuels.
10.3.16 Crankcase Internal Pressure—As measured by a gage or manometer connected to an opening to the inside of the
crankcase through a snubber orifice to minimize pulsations, the pressure shall be less than zero (a vacuum) and is typically from
25 mm to 150 mm (1 in. to 6 in.) of water less than atmospheric pressure. Vacuum shall not exceed 255 mm (10 in.) of water.
10.3.17 Exhaust Back Pressure—As measured by a gage or manometer connected to an opening in the exhaust surge tank or main
exhaust stack through a snubber orifice to minimize pulsations, the static pressure should be as low as possible, but shall not create
a vacuum nor exceed 255 mm (10 in.) of water differential in excess of atmospheric pressure.
10.3.18 Exhaust and Crankcase Breather System Resonance—The exhaust and crankcase breather piping systems shall have
sufficient internal volume and length dimensions such that gas resonance does not result.
10.3.19 Valve Stem Lubrication—Positive pressure lubrication to the rocker arms is provided. Felt washers are used on the valve
stems. A valve and rocker arm cover ensures an oil mist around the valves.
10.3.20 Cylinder Jacket Coolant Level:
10.3.20.1 Engine Stopped and Cold—Treated water/coolant added to the cooling condenser-cylinder jacket to a level just
observable in the bottom of the condenser sight glass will typically provide the controlling engine running and hot operating level.
10.3.20.2 Engine Running and Hot—Coolant level in the condenser sight glass shall be within 61 cm (60.4 in.) of the LEVEL
HOT mark on the coolant condenser.
10.3.21 Basic Rocker Arm Carrier Adjustment:
10.3.21.1 Basic Rocker Arm Carrier Support Setting—Each rocker arm carrier support shall be threaded into the cylinder so that
the distance between the machined surface of the valve tray and the underside of the fork is 19 mm ( ⁄4 in.).
10.3.21.2 Basic Rocker Arm Carrier Setting—With the cylinder positioned so that the distance between the underside of the
cylinder and the top of the clamping sleeve is approximately 16 mm ( ⁄8 in.), the rocker arm carrier shall be set horizontal before
tightening the bolts that fasten the long carrier support to the clamping sleeve.
10.3.21.3 Basic Rocker Arm Setting—With the engine on TDC on the compression stroke, and the rocker arm carrier set at the
basic setting, set the valve adjusting screw to approximately the mid-position in each rocker arm. Then adjust the length of the push
rods so that the rocker arms shall be in the horizontal position.
11. Engine Fit-for-Use Qualification
11.1 Before conducting either of the fit-for-use tests, operate the engine on an aviation gasoline or reference fuel blend in
compliance with the basic engine and instrumentation settings and standard operating conditions for approximately one hour to
bring the unit to temperature equilibrium.
11.2 Fit-for-Use Qualification After Maintenance—After each top overhaul and whenever any maintenance has been performed
other than coolant or lubricant fluid level adjustment or spark plug replacement, the engine shall be qualified as fit for use by
establishing its power curve.
11.2.1 Test the reference fuel blend of isooctane + 6.0 mL of TEL per U.S. gallon under standard operating conditions at a constant
manifold pressure of 135.4 kPa (40 in. Hg) while varying the fuel flow from lean to rich to cover the fuel-air ratio range from
approximately 0.07 to approximately 0.10.
11.2.2 Obtain at least five IMEP versus fuel-air ratio data pairs. Plot the data and fit a smooth curve to determine the maximum
IMEP.
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11.2.3 The engine is fit for use if the maximum IMEP of the po
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