alternator belt

[m_galligan]

On Sunday I noticed the ammeter going back to zero while the engine was on and the battery needed charge. The belt was spinning the alternator. Last night I noticed that the alternator had slipped down on the adjusting arm, so that the alternator belt, although in place, was very loose. This belt is a 25" motorcraft, only a week old (but it's been a long week for this boat!). When I tightened the alternator to the max. extent of the arm, the belt was still too loose for my taste. I have a single output alternator which was installed by a shop around 1995.

1. Can the alternator spin, maybe with a slightly loose belt, and generate too little output voltage to be useful?

2. I have always used a 25" belt. Is it practical to go to a 24" belt to get more tightness at a lower position on the arm? I have the Moyer alt. arm attached to the Moyer water jacket plate with welded on bracket.

3. I like to set the belt so that along one side of the belt there is 3/4" of play. That is, I can wiggle the belt from a position 3/8" to the right of it's normal position, to 3/8" left of it's normal position. 3/8 + 3/8 = 3/4, right? How much freeplay should there be here?

4. Besides length, what parameters guide the selection of a belt for the Atomic 4?

Thanks,
Marty (moored in Beverly, MA)

[Kurt]

From what I have read, there should be about 1/2" of flex - you should be able to push the belt in 1/2" - in the center of the longest span on the belt between pulleys. This should be the span from the alternator pulley to the assessory drive pulley. If trying a shorter belt doesn't work for you, Indigo sells a longer then stock adjusting arm for the alternator. I use one of those because I couldn't get my belt tight enough after changing over to fresh water cooling.

[sastanley]

Marty, Hopefully you aren't seeing any belt residue. For my week long cruise, I realized (much later) I had the alternator mis-aligned. This ate away at the belt so that by the end of the week, I had the alt. at max adjustment and it was still slapping around, and black belt dust everywhere.

I've fixed the alternator mounting problem, but now that belt (with only 10-15 hours on it) is no good, so I replaced it. The new identical replacement is noticeably shorter with travel still available on the arm. I am running the Gates belt that is mentioned around various websites..I think that is the 24" belt.