Cummins/Onan 20W-20 — TIMING BUTTON THICKNESS

For the Cummins/Onan 20W-20.

Applies to: Cummins Onan 20W 20

Procedure

1. Mark flywheel in 0.1-inch (2.54 mm) graduations (about five marks each direction) from PC mark calculating required change button thickness.
2. Count the number of graduations from PC mark on flywheel to point of actual port closing.
3. Multiply the number of graduations times .003 inch (.076 mm) to determine the difference in thickness required for new button. One degree of crankshaft rotation equals the 0.1-inch gradua- tion or .003-in ch button thickness for timing. Example A. The port closing time is late by 3 gradua- tions or 0.3-inch (7.62 mm) as measured from the PC mark on the flywheel, Figure 34. FLYWHEEL FIGURE 34. TIMING MARKS Multiply 3 x .003" = .009" (3 x .076 = .228 mm. Since each flywheel mark equals .003 inch (7.6 mm) button thickness, the installed button is too thin by .009 inch (0.229 mm). This means a button .009 inch (0.229 mm) thicker than the one installed is required to time port closing so PC mark on flywheel aligns at the timing pointer when fuel flow stops. Example B. If PC timing is too early by 4 graduations multiply 4 x .003 = .012 inch (4 x 7.6 mm = 0.304 mm). In this case, a button .012 inch (0.304 mm) thinner than the one installed is required.

Source: manual:974-0251 Onan RDJF Engine Service and Parts Manual (3-1980).pdf. Figures and steps are as documented; always cross-check against the official manual and any later revisions for your exact serial number before servicing.