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Old 06-02-2017, 09:19 AM   #1
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Yanmar 6LYA-STP 370HP Alternator replacement

I think I need to replace my alternator on my 2002 Pilot 34. The existing alternator is Hitachi #129772-77200, 12v 55amps. I did some quick searches and I'm not seeing the 6LYA on some of the cross-reference charts and wondering if perhaps it is not the original alternator and maybe the PO installed an incorrect replacement??
Here's a replacement on Amazon, for example:
https://www.amazon.com/ALTERNATOR-YA.../dp/B008Y3PA3C
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Old 06-02-2017, 09:37 AM   #2
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Should be 80a?

Just found this spec sheet, showing 80 amp?
http://www.taurus.gda.pl/uploads/ory..._datasheet.pdf
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Old 06-02-2017, 06:01 PM   #3
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Yes, the 6LY alternator is rated for 80 amps.

You can buy one from Yanmar and pay close to $1,000 I suspect, or get the part number and buy a real Hitachi for probably 1/3, or buy a Chinese knock off for less than $100. Here is a page of them on Amazon https://www.amazon.com/s/ref=nb_sb_n...6LY+alternator

But why do you think that you need a new alternator?

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Old 06-02-2017, 08:36 PM   #4
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Any alternator that meets the needs of the DC system will work. Engine makers don't make alternators., starters, injector pumps and so on. They buy them in bulk from companies that do. If you like OEM prices, just get a replacement from them. Otherwise find the make and get one that fits your mounting, belts and wiring. Typical replacement replacement alternator is under $100. Ebay is a good place to start.
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Old 06-02-2017, 08:51 PM   #5
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The PO probably got a deal on the 55 amp one. I would go with the 80 amp one if the drive belt is big enough. However most stock belts will drive up to about 100 amps so you are probably good to go.
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Old 06-05-2017, 07:04 AM   #6
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Why do I need a new alternator? Long story, electrical power related. My house battery died. The starting battery for my generator died as well. I was thinking my charger was the culprit, but I put a meter on it and it seems to be ok. After putting new batteries in, had a 9 hour cruise to home port and my VHF and GPS were giving me "low power" warnings. I turned the generator on, which seemed to work. I know there are ways to test the alternator, but seeing that it is 55amp,for $80, I am just going to replace it with an 80amp unit and hope all is well after that.
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Old 06-05-2017, 07:55 AM   #7
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If you only have the 55A Hitachi then it probably would be good to upgrade to 80A. But that might not solve your problem. It could be a wiring problem. Measure the output voltage of the alternator directly at its terminals. If it is 13.0 or greater with no shore power charger charging, it is ok.

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Old 06-05-2017, 08:01 AM   #8
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Greetings,
Mr. JD. Agreed. Go with the after market 80a. A number of automotive shops (O'Reily, Advance Auto, NAPA-just guesses but someone does free testing) will test for free. IF the suspect unit checks out OK, keep it as a spare.
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Old 10-12-2017, 09:05 PM   #9
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are you using the internal regulator?
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