Saturday, August 14, 2010

Stretch that belt

Eolian's original alternator was equipped with a non-standard pulley - larger than the regular automotive one. The adjustable bracket that holds the alternator was designed to fit using this pulley. That is, standard belts worked with it. When that original alternator failed, I replaced it with a standard 80 amp automotive alternator, with a standard pulley*. But now the belts available were either too short or too long.

The fix? Remanufacture the alternator bracket. I took several pictures of the front of the engine, with the alternator in various positions. I enlarged these until they were life-sized, and then laid out a new bracket on them. The end product used portions of the original bracket (to avoid machining), with a segment spliced in. Welded up and painted, it looks pretty good,and it works great.

* Most diesel engines (having no distributor) use pulses from the alternator to run the tachometer. When you change the alternator pulley (or switch to an alternator with a different number of poles), the tachometer will need to be recalibrated.


  1. What kind of "automotive" alternator is it? Who made it? 80 amps is pretty muscular for an automotive alternator, isn't it?

    Rick at

  2. Hi Rick -

    No, not at all. With the modern cars with heavy electrical demand (electric windows, electric cooling fan, window defrosters, seat heaters, etc), 80 amps is actually kind of light. My 1985 TransAm has a 100 amp alternator in it.

    This one is a Delco 10si wound for 80 amps. They can be had for around $100... check your automotive parts store. I think a 12si would be a drop-in replacement, and it has better cooling - a better choice.

    But please note: automotive alternators are not rated for use on marine *gas* engines - they are not explosion-proof (not an issue with a diesel).



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