Alternator Belt 121850-42280 for Yanmar 4LHA 4LH Marine Diesel Engine
Alternator Belt 121850-42280 for Yanmar 4LHA 4LH Marine Diesel Engine
Product Overview
Alternator belt 121850-42280E for Yanmar 4LH and 4LHA marine diesel engines, the belt that drives the alternator off the crank pulley. It replaces 121850-42280E and 121850-42280, and it ships in a 200 x 250 x 50 mm pack at 170 g.
It fits the whole 4LHA family, from the DTE through to the STZP, and the 4LH family, from the DTE through to the WSTZY. These are the four cylinder Yanmars found in sail drives, workboats and small fishing vessels, where a belt that lets go means no charging and no water pump.
Alternator belts on a marine diesel fail slowly and then all at once. A glazed belt slips, the alternator stops charging, and the batteries go flat over a long day. A frayed belt can take the water pump belt with it. Keeping a spare on board is cheaper than a tow.
Specifications
| Specification | Detail |
|---|---|
| Condition | New / New with tags |
| Type | Marine engine alternator belt |
| Fits | Yanmar 4LH and 4LHA marine diesel engines |
| Replaces | 121850-42280E, 121850-42280 |
| Contents | Alternator belt |
| Net Weight | 170 g including packaging |
| Pack Size | 200 mm x 250 mm x 50 mm |
| Warranty | 3 year |
OEM Cross Reference
| Component | OEM Part Numbers |
|---|---|
| Alternator belt | 121850-42280E |
| Alternator belt, alternate | 121850-42280 |
Compatible Engines
| Engine Series | Models |
|---|---|
| 4LHA | 4LHA-DTE, 4LHA-DTP, 4LHA-DTZE, 4LHA-DTZP |
| 4LHA | 4LHA-HTE, 4LHA-HTP, 4LHA-HTZE, 4LHA-HTZP |
| 4LHA | 4LHA-STE, 4LHA-STP, 4LHA-STZE, 4LHA-STZP |
| 4LH | 4LH-DTE, 4LH-DTZ, 4LH-HT, 4LH-HTE, 4LH-HTZ, 4LH-HTZAY |
| 4LH | 4LH-ST, 4LH-STE, 4LH-STZ, 4LH-STZAY, 4LH-TE |
| 4LH | 4LH-UT, 4LH-UTZ, 4LH-UTZAY, 4LH-WST, 4LH-WSTZY |
What's Included
| Component | Detail | Qty |
|---|---|---|
| Alternator belt | As pictured | 1 |
| Water pump belt | Not included, check it at the same time | 0 |
| Tensioner and pulleys | Not included | 0 |
Signs The Belt Needs Replacing
| What You See | What It Means | What To Do |
|---|---|---|
| Alternator warning light on at idle | Belt slipping | Check the tension, fit a new belt |
| Batteries going flat over a day | Alternator not turning fast enough | Fit the new belt |
| Squeal when the engine starts cold | Glazed or loose belt | Fit the new belt and set the tension |
| Cracks across the belt ribs | Rubber aged out | Fit the new belt now |
| Frayed edges | Belt running out of line | Check the pulley alignment, fit a new belt |
| Black dust around the front cover | Belt wearing on a pulley | Inspect the pulleys and fit a new belt |
Fitting Notes
| Step | Action |
|---|---|
| 1 | Check the engine model against the 4LH and 4LHA fitment tables |
| 2 | Isolate the batteries and disconnect the alternator wiring if needed |
| 3 | Loosen the alternator mounting bolt and the adjuster |
| 4 | Push the alternator in and slip the old belt off |
| 5 | Check the pulleys for rust, wear and alignment |
| 6 | Fit the new belt over the pulleys, not over the fan |
| 7 | Set the tension and tighten the adjuster, then the mounting bolt |
| 8 | Run the engine and check the belt runs true and the alternator charges |
Condition & Warranty
| Item | Detail |
|---|---|
| Condition | New / New with tags |
| Warranty | 3 year |
| Packaging | Sealed retail packaging |
Before You Buy
- Fits Yanmar 4LHA-DTE through to 4LHA-STZP
- Fits Yanmar 4LH-DTE through to 4LH-WSTZY
- Replaces 121850-42280E and 121850-42280
- Belt only, no tensioner or pulleys in the pack
- Check the water pump belt at the same time
- Keep a spare on board, a failed belt means no charging
- 30-Day Easy Returns
- Ships from our warehouse with tracking
Couldn't load pickup availability
Boat Owners' Review
Before You Buy
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