Changing the drive belt on an Universal diesel engine

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Change or replace the engine belt/ drive belt/ fan belt on your boats diesel engine

Here I used the drive belt on our Universal Westerbeke 25 XPB engine to demonstrate how to do it.

To change the engine belt/ drive belt on your good old boat's diesel engine we need the following tools (see image below). A flat screw driver to loosen hose clamps, a measuring tape and two wrenches. Our boat has a Universal Westerbeke 25 XPB engine and the wrenched are 1/2" and 7/16".


belt Universal25XPB 01 tool
The tools need to change a drive belt on an Universal Westerbeke 25 XPB.

First we need to loosen the alternator adjusting bolt which is located above the alternator (1/2" wrench for the factory mounted Universal 25XPB alternator). Just loosen it a bit we don't want to unscrew the bolt because chances are it pops out and disappears somewhere in the nirvana below the engine.

belt Universal25XPB 02 adjustmentBolt
The alternator adjusting strap bolt is easy to find on a Universal Westerbeke 25 XPB.

Next we need to loosen the base mounting bolt. The bolt sits as the name suggests at the base of the alternator and can be tricky to access. I found it the easiest to come in from the starboard side with a short wrench and I had just enough room to move the wrench and work on the bolt (7/16" on the 25XPB). Again we only need to loosen the bolt.

belt Universal25XPB 02 baseBolt
The base mounting bolt on the base of the alternator can be hard to access.

Now we can pivot the alternator on the base mounting bolt towards the center of the boat until the tension id of the belt and we can take it off. Well, almost we still have to remove the raw water hose coming from the strainer. Loosen the hose clamps where the hose connects to the raw water pump and take the hose off the barb connector. I had to poke under the hose with a small flat screwdriver to make it come off. Once this is done we can take the drive belt of the engine.

belt Universal25XPB 02 raw water Hose
The raw water hose pulled of the barb fitting at the raw water pump

Mount the new drive belt (fan belt part# 030475 for Universal Westerbeke 25 XPB or equivalent) then pivot the alternator back to tighten the belt. Tighten the alternator adjusting strap bolt a bit, bring the belt to the correct tension, then tighten the alternator adjusting strap bolt and the base mounting bolt. The recommended belt tension can be specific for each engine, for the Universal Westerbeke 25 XPB you should go for 1/2" deflection. This means when the belt is tightened, put your thumb in the middle of the belt (between alternator and water pump) and you should be able to push the belt down by about 1/2" but not more.

belt Universal25XPB 02 tension
Testing the engine belt/ fan belt on Universal Westerbeke 25 XPB for 1/2" deflection

Connect the raw water hose again, secured the hose clamps and you are ready to fire up the engine. Run it for about 5 minutes at idle then shut it down, recheck the belt tension and readjust if necessary.

belt Universal25XPB 03 fanbelt drivebelt 700x
The new engine belt (here a generic model) is doing its job.

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0 #1 Chrisu 2015-01-15 20:54
Hi Craig,
We had to replace our belt in Bundaberg, Australia and the only fitting belt we could find locally was this one:

V-belt TOP COGĀ®

Cheers, Chris

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