Important

Deleting the balance shafts in Honda H- and F-series engines can reduce parasitic drag, potentially freeing up horsepower, and improve oil pressure stability by eliminating unnecessary oil flow paths. This modification is typically performed during an engine rebuild or performance build.

Warning

This is an advanced modification that requires precise machining, tapping, and careful attention to cleanliness. Incorrect execution can lead to severe engine damage due to oil starvation or debris. Always confirm specific dimensions, thread pitches, and torque values with the official Honda factory service manual for your specific engine model.

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Overview of Balance Shaft Delete#

The balance shaft system in H- and F-series engines is designed to reduce engine vibration. For performance applications, these shafts are often removed to reduce rotating mass and parasitic drag. This process necessitates plugging specific oil passages that originally supplied oil to the balance shafts and their bearings, ensuring proper oil pressure is maintained throughout the rest of the engine.

Required Tools and Materials#

Before beginning, gather the following:

• Basic Hand Tools: Sockets, wrenches, screwdrivers.
• Taps and Dies: M8, M10, M12 taps (ensure sufficient length for deep passages).
• Set Screws:
  • M8 x 10mm hex set screws (DIN 913, 914, or 916 equivalent)
  • M10 x 10mm hex set screws (DIN 913, 914, or 916 equivalent)
  • M10 x 12mm hex set screws (DIN 913, 914, or 916 equivalent)
  • M12 x 12mm hex set screws (DIN 913, 914, or 916 equivalent)
• Large Plugs:
  • Machined aluminum plug for the front balance shaft oil passage (confirm dimensions against FSM).
  • M22 x 15mm plug for the rear balance shaft oil passage (confirm dimensions against FSM).
  • Alternative Large Plugs: 40mm and 25.4mm engine cooling jacket plugs (e.g., ZMZ-406 4061002030 for 40mm, FEBI 02544 for 25.4mm).
• Thread Sealant: High-strength, oil-resistant thread locker (e.g., Liqui Moly Fix-Gewinde or equivalent).
• Cleaning Supplies: Engine degreaser, brushes, compressed air, lint-free cloths.
• Bearing Puller: For removing the rear balance shaft bearing (can be a DIY setup).
• Measuring Tools: Calipers, depth gauge.

Disassembly and Preparation#

1. Engine Removal: The engine must be removed from the vehicle and disassembled to the bare block and oil pump for proper access.
2. Balance Shaft Removal: Remove both the front and rear balance shafts from the engine block.
3. Thorough Cleaning: Clean the engine block, main bearing girdle, and oil pump thoroughly. Remove all oil, debris, and old gasket material. Ensure all oil passages are free of obstructions.

Oil Pump Modification#

The oil pump contains several passages that supplied oil to the front balance shaft. These must be securely plugged.

1. Identify Passages: Locate the five oil passages in the oil pump housing that originally fed the balance shaft system.
2. Small Passages:
   • Tap the smaller passages to accept M8 x 10mm set screws.
   • Apply a high-strength thread sealant to the M8 set screws.
   • Install the M8 set screws flush or slightly recessed.
3. Front Balance Shaft Passage:
   • This is typically the largest passage.
   • Option 1 (Machined Plug): Install a custom-machined aluminum plug, ensuring a tight fit and sealing with thread sealant. Confirm exact dimensions with the factory service manual.
   • Option 2 (Cooling Jacket Plug): A 40mm engine cooling jacket plug can be used. Apply thread sealant to the plug and carefully drive it into place using an appropriate size socket (e.g., 32mm) as a driver.
4. Rear Balance Shaft Passage (Oil Pump Side):
   • This passage is typically smaller than the front one.
   • Option 1 (Threaded Plug): Tap the passage to accept an M22 x 15mm plug. Apply thread sealant and install.
   • Option 2 (Cooling Jacket Plug): A 25.4mm engine cooling jacket plug can be used. Apply thread sealant and carefully drive it into place using an appropriate size socket (e.g., 17mm) as a driver.
   • The oil channel under the rear balance shaft gear cover needs to be plugged to its full depth, approximately 25mm, as the oil channel is centrally located within the ~31mm bore.
   • The cover for the rear balance shaft gear is no longer necessary, but if reinstalled, use shorter bolts.

Caution

Ensure all plugs are installed securely and sealed properly to prevent oil leaks or loss of oil pressure. After tapping, thoroughly clean all metal shavings from the passages.

Engine Block and Main Bearing Girdle Modifications#

Oil passages within the main bearing girdle (often referred to as main bearing caps) and the engine block must also be plugged.

Main Bearing Cap Oil Passages#

1. Identify Passages: Locate the oil passages within the main bearing caps that previously supplied the balance shafts.
2. Tap and Plug:
   • For passages requiring M12 plugs, tap the channels to accept M12 x 12mm hex set screws.
   • For passages requiring M10 plugs, tap the channels to accept M10 x 10mm hex set screws.
   • Apply high-strength thread sealant to each set screw and install them flush.

Third Main Bearing Girdle Oil Passage#

This passage is critical and often overlooked. It's an oil feed from the main oil gallery to the rear balance shaft's middle bearing.

1. Locate Passage: This passage is found in the third main bearing girdle. It's a double channel: a main channel approximately 20mm deep, with a smaller 9mm diameter hole extending deeper towards the balance shaft bearing. It can often be illuminated from the oil pressure sensor port for verification.
2. Tap Deep Channel: This deep channel requires an M10 tap. A standard tap may be too short; an extended tap or a tap extension (e.g., 1/4" drive extension with pliers for rotation if no suitable tap wrench is available) may be necessary to reach the full depth.
3. Install Plug: Apply high-strength thread sealant to an M10 x 12mm hex set screw and install it securely into the tapped passage.

Note

After tapping any passage, use compressed air and appropriate cleaning solutions to remove all metal shavings before installing plugs.

Rear Balance Shaft Bearing Removal#

The rear balance shaft bearing, located in the engine block, should be removed to prevent oil from pooling in the unused bore and to eliminate any potential for future issues.

1. DIY Puller Method:
   • Obtain an M10 x 150mm bolt, an M10 nut, and two washers.
   • Use a 14mm socket and a 27mm socket as spacers/drivers.
   • Assemble the bolt, washers, nut, and sockets to create a makeshift puller to carefully extract the bearing.

Reassembly and Verification#

1. Final Cleaning: Before final engine assembly, perform a meticulous cleaning of the entire block and all components to ensure no debris remains.
2. Oil System Priming: After engine assembly, always prime the oil system before the initial start-up to ensure oil pressure is established.
3. Oil Pressure Check: Monitor oil pressure closely during the initial engine start and subsequent operation to confirm proper function. Consult the factory service manual for expected oil pressure ranges.

Tip

Consider installing an aftermarket oil pressure gauge for continuous monitoring, especially in performance applications.