Maintaining Belt Tension

The belt tension jack is about to justify its $20 cost

I don’t know about you, but for the longest time I always had problems getting my diesel’s alternator drive belt tensioned correctly. For starters, the engine is mounted backward, so to check the belt tension I first have to empty the cockpit locker, then climb into it and contort myself until I can get my arms and head under the cockpit sole and in the right position to reach the belt and pulleys. Fortunately, the belt always seems to need adjusting, so it’s never a wasted effort.

Beyond that, what really annoyed me was that after the usual rigmarole of loosening the pivot bolt and the pinch bolt on the adjusting arm, and then levering the pulleys apart with a long screwdriver until the tension felt right, then tightening the bolts again, the belt was always a little looser than I wanted. Inevitably, the screwdriver would slip or I’d misjudge the tension, or both. There was just no getting around the fact that it was one of those jobs you really need three hands for, and the result of having only two was an engine coated in that fine black dust that comes off poorly adjusted drive belts—not to mention frequent trips down to the dungeon to do it all over again.

Look, Ma, one hand—and no slippage or skinned knuckles

Then one day I discovered the romantically named Belt Tension Jack. Suddenly belt tensioning not only lost all its emotional tension, it even acquired a certain elegance.

This clever tool has one purpose and one purpose only: to push two pulleys apart, thereby applying tension to the relevant belt. Juggle it between the pulleys you want to separate, and then crank on the hexagonal body with a wrench to extend a threaded rod with a curved horn on its end until the belt is properly tensioned. After that you can nip up the nut on the pivot bolt and tighten the pinch bolt on the adjusting arm at your leisure, humming a merry tune as you go. Brilliant! There’s nothing like using the right tool for the job, especially a tool you had no idea existed.

The belt is sweetly tensioned, and I’m about to tighten up the bolts and call it a day

This is one of those little things that turns an unpleasant chore into a simple and quick maintenance task. You can buy these nifty tools from MSC Direct for around $20.


Belt Love

• A belt that’s too tight can cause wear on pulley bearings, and one that’s too loose can affect alternator output

• As a rule of thumb, if the belt deflects no more than half an inch when firmly poked with a finger, tension is about right

• Belts are not expensive and should be replaced annually along with engine oil and fuel filters. Keep the old one as a spare

• If you’ve installed a new belt, check its adjustment after a few hours of motoring. It will have loosened and may need retensioning

• Clean that nasty black dust off your engine and alternator. It can foul up the alternator’s delicate interior works. A sponge or rag coated in WD40 works well

Most Read on Sail

Also Popular on Sail


2 comments on “Maintaining Belt Tension

Leave a Reply