Detroit Diesel — Tapping Top Plug Bore
Repair & overhaul · Rear oil gallery top plug bore
From a Detroit Diesel service manual — check it applies to your exact model before use.
Before you start
- EYE INJURY: To avoid injury from flying debris, wear a face shield or goggles.
Procedure
- Loosen the Air Fitting Adapter (J-47485-3) set screw.
- Move the Air Fitting Adapter (J-47485-3) to the bottom plug bore and tighten set screw.
- Clean and inspect tap for damage before tapping the top hole; a spare tap is included in the kit.
- Apply a light coat of clean engine oil to the shaft of the Tap (J-47485-5) and install the Tap Guide Assembly (J-47485-6) into the top hole of the Adaptor Block (J-47485-1).
- Fully seat the Tap Guide (J-47485-2) into the Adaptor Block (J-47485-1) and tighten the set screw.
- Connect regulated and filtered air supply at 15 psi to the Air Fitting Adapter (J-47485-3).
- Using light force, start the tapping process. Ensure the tap is well lubricated.
- Back the tap off every ¼ turn. The tap will bottom out on the tap stop.
- Turn off shop air and loosen the tap guide assembly set screw. Remove Tap Guide Assembly (J-47485-6).
- Check and clean the newly tapped hole.
- Check the front face of the tapped hole for burrs. If burrs are present, lightly stone the surface.
- Disconnect shop air from the Air Fitting Adaptor (J-47485-3).
- Loosen the two M10 x 1.5 attaching bolts and remove the Air Fitting Adaptor (J-47485-3) and Adaptor Block (J-47485-1).
Tools required
Tool links are Amazon searches (affiliate links); manufacturer special tools may only be available from a dealer.
Specs & values
- Air supply: 15 psi
- Back tap off every ¼ turn
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.