ASTM D6891 Standard Test Method for Evaluation of Automotive Engine Oils in the Sequence IVA Spark-Ignition Engine
12. Calculation or Interpretation of Results
NOTE 13 - The summary of results and calculations are recorded on the appropriate report form.
12.1 Camshaft Lobe Wear - Use a surface roughness meter (profilometer) to measure the change in profiles across the worn cam lobe. Each lobe usually has an unworn edge at the front of the lobe, and at the rear of the lobe. Use these unworn edges to define a two-point reference line, and measure a maximum depth of wear.
12.1.1 For each lobe, make seven profilometer traces, scribing across the lobe. The seven locations on each lobe are: at the nose, which is 0° (zero)° cam lobe; +/- 4°; +/- 10°; and +/- 14°. Locate the nose by reading the highest profilometer position (to within 0.5 µm) on the unworn cam lobe surface.
12.1.2 Affix a 360° wheel a minimum of 250 mm diameter or an optical angle encoder to the front of the camshaft. Resolution of the degree wheel is 1° or better. After locating the lobe nose, determine the degree wheel zero reference mark. When viewed from the engine front, the camshaft normally rotates clockwise. When viewing the camshaft front, the plus direction is before cam nose top center. The minus direction is after the cam nose top center. Use this same sign convention for profilometer measurements.
12.1.3 The maximum deviation (Wt) of the worn nose profile (phase-correct filtered waviness profile) from a deduced unworn profile (reference line) is the wear value for that cam lobe location. (Report individual wear measurements to a resolution of one half of 1 µm, or better, in the range of 0 µm to 30 µm wear; and to a resolution of 1 µm, or better, in a wear range greater than 30 µm wear.)
12.1.4 For an individual lobe, the lobe wear is a mathematical summation of the Wt values for the seven defined locations on each lobe. Record these measurements on the appropriate report form.
12.1.5 Average (equal weighting) the lobe wear values for the twelve lobes of the camshaft to determine the single test result (average cam wear, ACW) (reported to 0.01 µm). Adjust for laboratory severity as shown in the ASTM Lubricant Test Monitoring System document which can be found at www.dgaequipment.com. Record this severity-adjusted value as Average Cam Wear Final (ACWFNL) on the appropriate test report form. ACWFNL is the primary result from this test method. When negative values are encountered for Average Cam Wear Final, record zero as the Final Average Cam Wear result.
12.2 Oil Analysis - The results from the used oil analysis are recorded on the appropriate report form.
12.2.1 Oil Sampling - Take a 10 mL oil sample of the new oil, used oil at 25 h, used oil at 50 h, and used oil at 75 h. Remove used oil samples during the transient portion of Stage II (near end of cycle 25 h; 50 h; 75 h). Take a 100 mL sample of drain oil at the end of the test (100 h).
12.2.2 Wear Metals - Measure the used oil samples (25 h; 50 h; 75 h; 100 h) for wear metal concentration (mg/kg), using Test Method D5185. Report iron and copper concentrations.
12.2.3 Kinematic Viscosity - Determine and report the kinematic viscosity (at 40 °C) for the new oil sample and the used oil sample at 100 h, using Test Method D445.
12.2.4 Fuel Dilution - Measure the mass percent fuel dilution of the used oil sample at 100 h. Fuel dilution typically ranges from 3.5 % to 7.0 %. (Ifthe fuel dilution exceeds 7.0 %, the valve-train wear test results may not be interpretable.) Use the following procedure to determine fuel dilution.
12.2.4.1 Fuel Dilution - mass percent by gas chromatography using Test Method D3525 as modified:
(1) Use C16 (hexadecane) instead of C14 (tetradecane) for the internal standard (1 mL injector volume).
(2) Define all components lighter than C16 as fuel.
(3) The integrator should establish a horizontal baseline under the output curve.
(4) Column Details - Stainless steel (SS) 1830 mm by 3.2 mm, solid support: Dexsil 300 10 %, 80 to 100 mesh.
(5) Temperature Details - Oven temperature 60 °C to 320 °C, rate of change of temperature 8 °C/min, held at 320 °C for 16 min to elude oil.
