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Perkins Generator Set Fan Belts And Crankcase Breather Maintenance

Apr. 09, 2018

Any spare parts of engine is important for a diesel generator set. In this article, you will learn the maintenance procedures of Perkins 4000 Series diesel genset. The post mainly introduces the genset belt, fan bearings and crankcase breather related technical knowledge.


WARNING!! Disconnect batteries or any other means of starting.

Remove the mesh guard around the fan belts, grease the fan and jockey pulley bearings Fig.23 using high melting point lithium based grease (e.g. Shell Alvania R.A.)

Check the tension and condition of the fan belts. Using a spring balance and rule, or a belt tension indicator, check that the force compares with the kgf (lbf) values shown below for the correct belt deflection. See Fig.23.


kg Force

fb Force

11 mm

3 - 4.3

6.67 - 9.47


Fan belts if worn, should be replaced as a complete, matching set. Individual belts should NOT be replaced.

To adjust slacken the jockey pulley pivot and adjuster bolts, and operate the jockey pulley lever.

Moving the jockey pulley lever outwards will tension the belts and inwards will slacken the belts.

The correct tension is obtained by measuring the deflection at the mid point between the fan pulley and the crankshaft pulley when the above force is applied.

To apply the force place a rule across the outside width of the belts and attach spring balance as shown Fig.23 pull on the spring balance until the required force is reached and measure the belt deflection.


Adjust the position of the jockey pulley lever until the force on the spring balance and the belt deflection agree with the figures given above.

When using a belt tension indicator position the indicator on top of a belt at the mid center distance and apply a force at right angles to the belt deflecting it to the point where the lower marker is level with the top of the adjacent belt. Read off the force value indicated by the top edge of the upper marker. Having set the tension on the belts, tighten the adjuster and pivot bolts. refit the fan belt guard.

NOTE: If the measured force falls within the values given,the drive should be satisfactory, if it is below the lower value under tensioning is indicated.

A new drive should be tensioned to the higher value to allow for the normal drop in tension during the running-in period. After the drive has been running for 30 minutes, the tension should be checked and re-adjusted to the higher value.



a) Small cracks on V-Belt Side and Base

Generally caused by lack of belt tension but excessive heat and/or chemical fumes can also lead to similar failure.

b) V-Belt swelling and softening

Caused by excessive contamination by oil, certain cutting fluids or rubber solvents.

c) Whipping during running

Usually caused by incorrect tensioning principally on long center drives. If slightly higher (or lower) tension does not cure the problem there may be a critical vibration frequency in the system which requires re-design or a banded belt (2 belts banded together to make a W belt).



WARNING!! Disconnect batteries or any other means of starting. When using compressed air or cleaning agents always wear eye protection, and protective gloves.


The crankcase breather is mounted on the side of the radiator Fig.24 and is connected to an elbow mounted on the gearcase by a flexible pipe Fig.26.

crankcase breather.jpg


The crankcase breather is mounted on the side of the thermostat housing Fig. 25 and is connected to a breather body mounted on the gearcase by a flexible extension pipe Fig.26.

Perkins crankcase breather.jpg

Unscrew the breather by turning it anti-clockwise, wash thoroughly using a suitable cleaning agent, shake as dry as possible, finally blow dry with compressed air then screw the breather firmly back into position.



1. Position of breather when engine is fitted with a radiator

2. Position of breather when engine is fitted with heat exchanger

3. Flexible pipe

4. Elbow

breather body.jpg


The crankcase breather is mounted on the side of the thermostat housing Fig.27 and is connected to the engine via a flexible pipe and elbow fitted on the front of the gearcase.

Perkins generator crankcase breather.jpg

To clean the breather remove the top cover and withdraw the two wire mesh elements and wash thoroughly using a suitable cleaning agent, Shake as dry as possible, finally blow dry with an compressed air. Refit the elements into the breather body, and fit the top cover firmly.

NOTE: When replacing the cover check the sealing gasket is in good condition and the cover has located on its dowel.

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