Yanmar SD20 Saildrive Workshop & Service Manual
Instant Answer & Quick Specs Box
Engineering Overview & Factory Specifications
The Yanmar SD20 Saildrive is an advanced marine propulsion lower unit engineered for auxiliary sailboat diesel engines (1GM10, 2GM20, 3GM30, 3JH2E, 2YM15, 3YM20, and 3YM30). Featuring an internal mechanical dog-clutch transmission with a 2.64 reduction ratio, dual rubber hull diaphragm sealing membrane, and high-efficiency hydrodynamic strut housing, the SD20 delivers reliable thrust with minimal drag. This official factory service manual (Publication No. EPB5547) covers lower gearcase disassembly, propeller shaft lip seal replacement, bevel gear shimming and backlash adjustments, diaphragm leak sensor testing, and sacrificial anode maintenance.
Critical Engineering Fasteners & Tightening Sequence
| Component / Fastener | Thread Size | Torque / Clearance Standard | Service Instructions & Lubrication |
|---|---|---|---|
| Upper Housing Clamping Bolts | M8 × 1.25 | 23.5 – 27.5 N·m (17.3 – 20.3 lb-ft) | Torque evenly in crisscross sequence; apply marine anti-corrosion grease |
| Lower Gearcase Retaining Bolts | M8 × 1.25 | 26.0 – 30.0 N·m (19.2 – 22.1 lb-ft) | Apply thread sealant to prevent galvanic seizure in seawater environment |
| Propeller Nut | Special Hex | 49.0 – 58.8 N·m (36.1 – 43.4 lb-ft) | Lock with cotter pin or safety washer tabs after torquing |
| Bevel Gear Backlash | Pinion / Crown | 0.10 – 0.20 mm (0.004 – 0.008 in) | Adjust with selective precision shims behind pinion bearing |
| Propeller Shaft End Play | Axial Clearance | 0.05 – 0.15 mm (0.002 – 0.006 in) | Check with dial indicator; renew dual back-to-back oil seals |
Complete Factory Service Chapter Directory
- 1. SD20 Saildrive General Specifications: Reduction gear ratio (2.64:1), dry weight (30 kg), oil capacity (2.2 Liters), and engine compatibility.
- 2. Upper Gear Housing & Dog Clutch: Input shaft splines, forward/reverse shifting fork, shift cam clearance, and detent spring inspection.
- 3. Lower Gear Housing & Propeller Shaft: Propeller shaft dual radial oil seal replacement, stainless wear sleeve inspection, and sacrificial zinc anode renewal.
- 4. Bevel Gear Shimming & Backlash Adjustment: Measuring tooth contact pattern using Prussian blue dye, pinion depth shims, and bearing pre-load.
- 5. Hull Bed Installation & Diaphragm System: Dual rubber sealing diaphragm replacement interval (5 years / 2000 hours), hull clamp ring torquing, and water intrusion sensor circuit.
- 6. Lubrication & Haul-Out Maintenance: Draining and pressure-testing gearcase (0.03 MPa for 3 min), gear oil filling procedure, and seawater intake strainer cleaning.
Heavy Equipment & Marine Mechanics: Free Interactive Calculation Suite
Calculate fastener stretch, torque unit conversions (Nm to ft-lbs), engine displacement, and compression ratio online in seconds:
Open Diesel Mechanic Calculators →Frequently Asked Questions
What type of oil does the Yanmar SD20 saildrive require?
The Yanmar SD20 saildrive requires 2.2 Liters (0.58 U.S. Gallons) of QuickSilver High Performance Gear Lube or SAE 80W-90 API GL-4 / GL-5 gear oil. Check oil level with the dipstick unscrewed resting on the housing rim.
How often must the Yanmar SD20 rubber diaphragm be replaced?
Yanmar recommends replacing the dual rubber hull sealing diaphragm every 5 to 7 years or immediately if the instrument panel water sensor buzzer is activated.
