Most Yanmars have a 35amp Hitachi as standard. At least every one I have seen. Don't know if I would go any bigger on a one lunger. Make a trip to your local alternator/starter shop. Save yourself a bunch of bucks. Recently told by my gf that she bought a 80 amp alternator from Yanmar, for nearly 600 bucks. I just upgraded mine to a 70 amp from a local rebuilder. Brand new, 70amp Hitachi, for 80 bucks. Don't get drug into the marine alternator deal. The difference in a marine alternator and a non marine, are little screens inside that stop sparks from escaping. These are intended to keep a hot spark from igniting gas fumes. Not needed on diesel motors.
Dear overtorqued and flatracker,
In the interim, since my first e-mail inquiry, I have paid $200 for a small alternator manufactured by Nippon Denso. Like my new Jabsco water pump, it is not original Yanmar equipment, so I am having to jury rig it into place. Once I get it mounted, it hope it works as well as the water pump. Anyway, thanks for your replies. Happy sailing!
I was experiencing fading batteries that were having difficulty starting my 2GM20. I thought that the Alt may have suffered an untimely demise.
I took the old 35 amp into the local Advance Auto parts and they tested it, yup, it was dead. They told me that it was the same frame as the NISSAN alternators and that they could have a 65 Amp on in 2 days for about $75. I did a Ebay search and found a 50Amp Hatachi for a Yanmar for under $100. I stayed with the marine version for the few extra $$...
Just posting this in case some one comes looking for an answer in the future.
The alternator on the YSE12 has no nameplate, but it looks similar to a Hitachi LR135-31 (not quite exact, but same mounting points). It has the Hitachi symbol embossed on the rear journal housing. The YSE instruction manual says its 25A. The service manual says its 25A, 14V @ 5000rpm.
One other note is that the idler shaft (PTO - power takeoff shaft) that drives the alternator & water pump sheaves is rated at only 2-3hp at 3000rpm for the YSE12, which means about a 50A replacement alternator would be the max. (if you can spare that much horsepower ;-)
If anyone has the model number for the 25A, please post it up.