Yanmar 3YM30 Service Manual page 42

(4) Adjust the tension of the alternator drive belt
When there is not enough tension in the V-belt, it will
slip and the cooling water pump will fail to supply
cooling water. Engine over-heating and the seizure will
occur.
When there is too much tension in the V-belt, the belt
will become damaged more quickly and the bearing of
the cooling water pump may be damaged.
Check and adjust the V-belt tension (deflection) in the
following manner.
[Notice]
Be especially careful not to splash engine oil on the
V-belt, because it will cause slipping, stretching and
aging of the belt.
1) Remove the belt cover. Check the tension of the V-
belt by pressing down on the middle of the belt
with your finger [approx. 98N(10kgf)].
The specified deflection should be as follows.
For used V-belt
For new V-belt
• "New V-belt" refers to a V-belt which has been used less than 5 minutes on a running engine.
• "Used V-belt" refers to a V-belt which has been used on a running engine for 5 minutes or more.
2) If necessary, adjust the V-belt tension (deflection).
To adjust the V-belt tension, loosen the set bolt for
the belt adjuster and move the alternator to tighten
the V-belt.
3) Visually check the V-belt for cracks, oiliness or
wear. If any, replace the V-belt with new one.
[Notice]
When the V-belt will be replaced with new one,
loosen the set bolt, move the alternator and also
loosen the V-pulley set bolts for the cooling water
pump. Remove the V-belt.
After replacing with a new V-belt and adjusting the
tension, run the engine for 5 minutes and readjust the
deflection to the value in the table above.
8-10 mm (0.315-0.393 inches)
6-8 mm (0.236-0.315 inches)
Bracket
22R1
2. Inspection and adjustment
Push
Alternator
V-belt
Belt adjuster
(3YM30)
Set bolt