How to Adjust a Yanmar 2GM Alternator Pulley

Written by robert osborne
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Yanmar Marine produces a wide range of marine diesel engine models for sailboats and powerboats. The Yanmar 2GM is a two-cylinder raw water-cooled engine, produced between 1980 and 1983. The 15-horsepower 2GM engine uses a 35-amp alternator. The 2GM alternator is belt-driven, and relies on proper tension to achieve a proper battery charge. If the alternator belt is too tight, on the other hand, damage to the belt or alternator bearings will occur.

Skill level:
Moderately Easy

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Things you need

  • Metric box wrench set
  • Pry bar
  • Ruler
  • Straight edge
  • Fish scale

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  1. 1

    Inspect the belt and alternator pulley. Replace a cracked or damaged belt. Ensure that the belt and pulley are oil-free. Wipe off any oil with a rag.

  2. 2

    Check the alternator belt tension. Place a straight edge on top of the two pulleys. Hook a fish scale to the middle of the top belt. Pull downward until you obtain a reading of 9.98kg. Measure the distance between the straight edge and the deflected belt with a ruler. A properly adjusted belt will deflect about 3/8 inch.

  3. 3

    Adjust the alternator pulley by loosening the bolt in the alternator adjusting arm. Place a pry bar between the alternator and its mount. Gently lift the pry bar upward. Tighten the bolt in the alternator adjusting arm while you continue to lift up on the pry bar. Check the belt tension.

  4. 4

    Continue your adjustments until you achieve the proper belt tension.

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