Honda BF20A / BF25A service guide
Oil, gear oil, spark plugs and the service schedule for the Honda BF20A / BF25A (20 to 25 hp, four-stroke), from the factory service manual, plus how we service it in Hawaiʻi.
Models covered: BF20A (codes BAHS/BAHL) and BF25A (BAJS/BAJL), types SH, LH, SHS, LHS, SRS, LRS; 4-stroke 3 cylinder, 499 cm³, 3 carburetors, CDI.
Quick answers
- How much oil does a Honda BF20A / BF25A take?
- 1.6 L (1.69 US qt); 1.9 L (2.00 US qt) with filter.
- What engine oil does a Honda BF20A / BF25A use?
- SAE 10W-30, API SG, SF/CC, CD.
- What gear oil does a Honda BF20A / BF25A use, and how much?
- Marine SAE 90 hypoid gear oil, API GL-4 or GL-5. Quantity: 0.29 L (0.307 US qt).
- What spark plug does a Honda BF20A / BF25A use?
- NGK DR7EA or Nippondenso X22ESR-U, qty 3. Gap: 0.6 to 0.7 mm (0.024 to 0.028 in).
- How often should a Honda BF20A / BF25A be serviced?
- The factory schedule lists: First month or 20 hours; Every 6 months or 100 hours; Every year or 200 hours; Every 2 years or 400 hours. In Hawaiʻi's salt water we do a full yearly service every 200 hours or 1 year, whichever comes first, and a new engine needs its first (break-in) service.
- When should the water pump impeller be replaced on a Honda BF20A / BF25A?
- The factory schedule gives no replacement interval. In Hawaiʻi's warm salt water we replace it every 200 hours or 1 year, whichever comes first, because a worn impeller is the most common cause of overheating.
- What is the idle speed of a Honda BF20A / BF25A?
- 900 ± 50 r/min in neutral, warm.
- What is the propeller nut torque on a Honda BF20A / BF25A?
- 1 N·m (0.1 kgf·m), then tighten until the cotter pin fits, maximum 35 N·m (3.5 kgf·m, 25.3 lbf·ft); new 3.0 mm cotter pin.
Maintenance specs
| Engine oil | SAE 10W-30, API SG, SF/CC, CD |
|---|---|
| Engine oil quantity | 1.6 L (1.69 US qt); 1.9 L (2.00 US qt) with filter |
| Oil filter | Hand tight, then with wrench 07HAA-PJ70100 to 11 N·m (1.1 kgf·m, 8.0 lbf·ft) |
| Engine oil drain bolt | 23 N·m (2.3 kgf·m, 16.6 lbf·ft), new sealing washer |
| Gear oil | Marine SAE 90 hypoid gear oil, API GL-4 or GL-5 |
| Gear oil quantity | 0.29 L (0.307 US qt) |
| Gear oil drain and level plugs | 3.5 N·m (0.35 kgf·m, 2.5 lbf·ft), new washers; level plug in first, then drain plug |
| Spark plug | NGK DR7EA or Nippondenso X22ESR-U, qty 3 |
| Spark plug gap | 0.6 to 0.7 mm (0.024 to 0.028 in) |
| Spark plug tightening | New plug 1/2 turn after seating; reused plug 1/8 to 1/4 turn after seating |
| Idle speed | 900 ± 50 r/min in neutral, warm |
| Thermostat | Starts opening 72 °C (162 °F); fully open 82 °C (180 °F); lift more than 3.0 mm (0.12 in) |
| Propeller castle nut (14 mm) | 1 N·m (0.1 kgf·m), then tighten until the cotter pin fits, maximum 35 N·m (3.5 kgf·m, 25.3 lbf·ft); new 3.0 mm cotter pin |
| Valve clearance, cold | IN 0.10 to 0.14 mm (0.004 to 0.006 in); EX 0.18 to 0.22 mm (0.007 to 0.009 in); lock nut 8 N·m (0.8 kgf·m, 5.8 lbf·ft) |
| Timing belt | Automatic tensioner; inspect, replace if worn or damaged. |
Service schedule
The factory maintenance intervals, with what is replaced and what is checked at each. Rows marked Hawaiʻi are our shop's yearly service for salt water use.
First month or 20 hours
Replace: engine oil, oil drain plug gasket, gear case oil, gear case plug gaskets
Check: spark plugs
Every 6 months or 100 hours
Replace: engine oil, oil drain plug gasket, gear case plug gaskets, propeller cotter pin
Check: fuel filter, gear case oil
Every year or 200 hours
Replace: engine oil, oil drain plug gasket, gear case oil, gear case plug gaskets, propeller cotter pin, water pump impeller
Check: spark plugs, fuel filter, thermostat
Every 2 years or 400 hours
Replace: engine oil, oil filter, oil drain plug gasket, fuel filter, gear case oil, gear case plug gaskets, propeller cotter pin, water pump impeller
Check: spark plugs, thermostat
We replace the water pump impeller at every service from 200 hours up, which can be sooner than the factory schedule, because of Hawaiʻi’s warm salt water.
Source: Honda BF20A/BF25A Shop Manual, part no. 66ZV700. Specs can change by model year and serial number, so always confirm your exact model from the serial tag on the clamp bracket.