Valve Clearance Adjustment on Honda BF20A-BF25A, BF25D-BF30D Outboard Motors
Valve Clearance Inspection
Valve clearance inspection and adjustment must be performed with the engine cold.
Inspection Steps:
- Remove the engine cover, flywheel cover, or recoil starter.
- Disconnect the breather tube and oil return tube from the cylinder head cover. Remove the six 6 x 35 mm flange bolts and cylinder head cover.
- Remove the spark plugs and engine hanger bracket with caution to avoid water pump impeller damage.
- Manually turn the flywheel clockwise until the "T" mark on the flywheel aligns with the "I" mark on top of the flywheel cover or recoil starter mounting boss. The "T" mark on the cam pulley will align with the "T" mark on the cylinder head. In this position the No.1 piston is at top dead center of its compression stroke.
- With the engine in this position, check the intake and exhaust valve clearances by inserting a feeler gauge between the valve stem and the adjusting screw on the rocker arm.
- Turn the flywheel clockwise until the cam pulley turns an additional 240 deg. and the "UP2" mark align with the "T" mark on the cylinder head. This will put the No.2 piston at top dead center of its compression stroke. Check the intake and exhaust valve clearances on the No. 2 cylinder.
- Turn the flywheel clockwise until the cam pulley turns an additional 240 deg. and the "UP2" mark aligns with the "T" mark on the cylinder head. This will put the No.3 piston at top dead center of its compression stroke. Check the intake and exhaust valve clearances on the No. 3 cylinder.
Valve Clearance Specifications:
| Valve | Clearance (mm) | Clearance (in) |
|---|---|---|
| Intake | 0.10-0.14 | 0.004-0.006 |
| Exhaust | 0.18-0.22 | 0.007-0.009 |
Adjustment
If adjustments are necessary, proceed to adjustment:
- Turn the adjusting screw on the rocker arm to achieve the specified clearance.
- After adjustment, install the removed parts in reverse order of disassembly.
