Mando alt - replace regulator, or go to Delco?

F

freak007

Petty Officer 2nd Class
Joined
Jul 19, 2008
Messages
126
Yup, its me again... 1984 Mercruiser 120 (2.5L) with a 55 amp Mando alternator I am troubleshooting a charging issue I have...

When I first got the boat, the battery charge was low... but the boat started... we let it run on the 'muffs for about 30 minutes...

Took it out on the water for 30-45 minutes, and volt gauge would keep climbing until it would peg out... I figured it was still charging the battery and the gauge was not accurate...

Took it out again for 30-45 minutes after changing the prop - same thing, only this time when I went to pull the drain plug, I heard the battery hissing...

Decided to test it while running on a hose again... I slowly increased the throttle with my Snap-On multimeter hooked to the battery... I stopped at ~2200 RPMs because the voltage was over 17 volts :eek:

Excitation circuit and sensing circuit tested good... I know my regulator is bad...

When I checked pricing on a new regulator it is $65+... I can get a Delco 10SI style one wire marine alternator for under $75... the Delco is a 63 amp that supposedly replaces the 37 Amp Delco with Mercruiser PN 69729 that was also used on my engine...

Does anyone know if I will run into any issues (brackets, dependability etc) by going to the 1 wire??
 
Don S

Don S

Honorary Moderator Emeritus
Joined
Aug 31, 2004
Messages
62,321
Re: Mando alt - replace regulator, or go to Delco?

It's always going to be easier to troubleshoot if things are as shown in the service manual. If you have a good alt/starter repair shop, that would be the best way to go. Cheaper to in the long run when you have to start redoing all the brackets and pulleys to get the belts to line up and all the wires dead ended that you don't need NOW, but may later.
 
F

freak007

Petty Officer 2nd Class
Joined
Jul 19, 2008
Messages
126
Re: Mando alt - replace regulator, or go to Delco?

the Delco is in the service manual... I really have no concerns about troubleshooting a 1 wire alternator... going from the Mando to the 1 wire Delco should be as simple as capping the exciter and sensor wires and hooking the output wire up... assuming the brackets and pulleys are the same...

I am wondering if the brackets are the same between the two units? I have only been able to find 2 PN for a alternator bracket (16738A1 for the lower portion, and 58333 for the adjustment arm)...

Are all the 4 cylinder brackets the same, no matter which of the 4 available alternators you got? Are all the pulleys the same?
 
Bt Doctur

Bt Doctur

Supreme Mariner
Joined
Aug 29, 2004
Messages
19,344
Re: Mando alt - replace regulator, or go to Delco?

I have replaced the mando with the gm on M/C 350 motors with no issues
on belts ,pulleys, etc.
 
R

Robj

Lieutenant
Joined
Mar 22, 2007
Messages
1,441
Re: Mando alt - replace regulator, or go to Delco?

The biggest issue in replacing the alternator with a different one is getting the pullies and belt lined up properly. If you can do that then I would replace it. I threw my old three wire alternator in the garbage, actually recycling, and got a single wire Delco with no regrets. Had lots of $$ left over for beer!

Have a great day,

Rob.
 
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