Detroit Diesel — Adjust Governor Gap (Limiting Speed Mechanical Governor)
Adjustments
From a Detroit Diesel service manual — check it applies to your exact model before use.
Before you start
- Do not overspeed the engine
Procedure
- Back out the buffer screw until it extends approximately 5/8" from the locknut.
- Remove the high-speed spring retainer cover.
- Start the engine.
- Loosen locknut and adjust idle speed adjusting screw to obtain desired engine idle speed (550-750 rpm current or 450-550 rpm former).
- Stop engine; remove governor cover and lever assembly and valve rocker covers; discard gaskets.
- Start and run engine between 1,100 and 1,300 rpm by manual operation of the differential lever.
- Check gap between low-speed spring cap and high-speed spring plunger with a feeler gage; gap should be .002"-.004".
- If incorrect, reset the gap adjusting screw.
- On governors without starting aid screw, hold gap adjusting screw and tighten locknut.
- Recheck gap with engine operating between 1,100 and 1,300 rpm and readjust if necessary.
- Stop the engine.
Tools required
- feeler gage Amazon
Tool links are Amazon searches (affiliate links); manufacturer special tools may only be available from a dealer.
Source: Detroit Diesel service manual. Steps and values are as documented; always cross-check against the official manual and any later revisions for your exact serial number before servicing.