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View Full Version : Want to upgrade Alt in the Ol' Girl (83 S&S 351W) few questions...


03geetee
03-20-2014, 09:52 AM
Hey guys,

Interested in giving the 31 year old alternator on my PCM 351 a proper rest. I have a feeling that it charges my 1000CCA interstate just enough on my short 2-3 day weekend trips to keep things moving. My thought is my battery is so large and with no other electrical demand other than the bilge pump and starting duty, the battery has enough juice from sitting on the tender for a while to handle it.

I know it is the factory unit and I have considered rebuilding it however I hear a lot of people with older boats doing the 105 amp unit from DB. I know I have more then one wire coming out of my original unit so I am curious to know how the new unit works. I have also read that one of the bolt holes will need to be enlarged slightly, no big deal. What about belt and pulley sizes does it remain the same?

What else am I missing to do this mod, I don't have a stereo yet but would like one down the road. Also having my big ol' interstate properly juiced would be nice.

JTR

1redTA
03-20-2014, 10:06 AM
I did nothing extra to bolt the 105 db alt in my 81, except add an 8 gauge wire from the charging lug to the battery (in addition to the stock wire)

Xjet2011
03-20-2014, 07:22 PM
I put a DB alt on my 1990 Prostar. Had the proper same size pully but had to drill out the mounting hole a slight bit. Ran one wire to the Hot battery lead. Simple and quick.

bsloop
03-21-2014, 09:24 AM
I would have the old unit tested before assuming. Any parts store can spin it up or better yet, seek an electric rebuild shop. My local can rebuild with much better parts than the cheap import pieces DB uses for the same $$.
(Nothing against DB for a cheap, new unit. I have used theirs before too.)

DB should also have a 3 wire that will work just fine. They like to push the single wire because it is a little cheaper and universal. With no additional power demands, any amperage alt should be fine.
If you have the battery on a Battery Tender and feel it is still weak, look for external draws or weak/corroded connections. Both are very likely on an older boat and more likely the cause.

03geetee
03-21-2014, 12:11 PM
I would have the old unit tested before assuming. Any parts store can spin it up or better yet, seek an electric rebuild shop. My local can rebuild with much better parts than the cheap import pieces DB uses for the same $$.
(Nothing against DB for a cheap, new unit. I have used theirs before too.)

DB should also have a 3 wire that will work just fine. They like to push the single wire because it is a little cheaper and universal. With no additional power demands, any amperage alt should be fine.
If you have the battery on a Battery Tender and feel it is still weak, look for external draws or weak/corroded connections. Both are very likely on an older boat and more likely the cause.

No draws,, new cables, new battery (2 years old) new starter and cables. Like I said I don't think the alternator is failed I think it is failing. Boat is just fine and keeps firing between battery tender usage (only while Im away and boat is in garage) never use it on the dock.

JTR