Thursday, December 8, 2011

Replacing An Alternator

The tachometer for Drift Away's starboard engine stopped working on our run into Annapolis.  While changing fuel filters, I had noticed that a copper tab with wires connected to it at the 11 o'clock position had snapped off the alternator and was being held by a black wire coming out off the alternator.  It was swinging around while underway and shorting against the case, so I zip-tied it in place.  On close inspection I found that the black wire was now broken off.

One of our favorite places for food and drinks is Davis' Pub here in the Maritime Republic of Eastport.  Friend Miro and I were leaving the other night when I bumped into an old internet friend, Bernie Jakits, who owns Roguewave Yacht Sales.  Bernie was there with Kevin McPadden, the manager of Annapolis Harbor Boat Yard, and their wives.  Bernie introduced us and said that Kevin is the only guy in the marine biz in Annpolis who wouldn't screw over a customer.  I don't know if that's true or not.  Bernie is, and has always been, very blunt and direct, but Kevin and his wife seemed like good folks.   So I told Kevin about my alternator problem and he said to bring it in.

Whenever I do a boat project like this, I like to take photos of the before and after.  I used to draw diagrams, but digital pics are much easier.  This is the old alternator before I removed it.

There are three sets of wires.  A yellow wire at 3 o'clock, a set at 6 o'clock, and a set at 9 o'clock.  Well, the set at 9 o'clock isn't there because the copper tab where the red wire is broke off, and the black wire that was holding it up there also broke off. 

So I removed the alternator, stuffed it in a back pack and hied myself a few blocks down to Annapolis Harbor Boat Yard. It's a busy place, but Kevin took the alternator.  Kevin contacted me the next day.  The old one would cost more to rebuild that getting a new one, so I gave him the go ahead to order two.  I might as well replace the other one while I'm at it.

After helping Miro with his alternator problems, I learned that you don't just want to buy something off the internet and then try to make it fit.   The new alternator pully must be the same diameter as the old, otherwise it will spin too fast or too slow.  It must also be in alignment with the flywheel and water pump, and must fit the brackets.  This is a job for experienced pros.

You can see the bottom bracket in this pic.  The new one sould have to fit there perfectly, and the pulley would have to line up the fan belt exactly.

Kevin had two replacements for me the next day.  The new Prestolite 8RGs were replacements for the 8MRs.  I looked at the electrical connections on the back and they were different from the old alternator, but I figured I could sort it out.  Back at the boat, the new alternator bolted on perfectly, an exact fit.   Now what to do about the wiring?  The new alternator came with everything nicely labeled.

This was great, but the old alternator had nothing labeled.  What's positive and what's negative?   I put a call out to my internet friends and one quickly had a link to a Prestolite tech manual page.  I found what I thought was my alternator from googling around the internet, a 8MR2018K, but I called Prestolite tech support anyway to confirm this  The tech support guy said his name was "Kevin".   I'm starting to think that service people just make up names and they all use "Kevin".  I emailed a photo of my old alternator, and "Kevin" confirmed it was the 8MR2018K.  So I connected all the wires to their respective places and I fired up the starboard engine.  The tachometer still didn't work.

I called "Kevin" at Prestolite tech support back and told him of my problem.  He said it was no biggie, just connect the tachometer wire to the AC Tap post.  I told "Kevin" that the old alternator didn't have an AC Tap post, just postive, negative, and ignition switch connections.  "Kevin" was baffled.  If "Kevin" couldn't figure it out, there's no way a DIYer like me could, so I put in a call to "Kevin" at Annapolis Harbor Boat Yard.  They're really busy winterizing boats but he's going to send a mechanic here the beginning of next week.  So that means that, once again, we are sitting in a marina waiting to fix the boat.  I suppose we could go on without the tach on the starboard engine and synchronize the two engines by sound, but being a computer guy, I like to know, not guess.  So here we sit.

I'm guessing the mechanic's name will be "Kevin".  


  1. Everyone else in the marine business will screw a customer--what a left handed compliment when introducing someone--you can be sure they were talking about how to do just that.

  2. Well I'm a Kevin and won't sell you anything! However I will be watching to see the outcome of htis problem, as I need to replace the voltage regulator on Autumn Dream and am currentlly investigation some of the "smart" voltage reguators sold by Balmar through Defender. So confusing since I have a very simple electrical system wiht solar pannels. Keep up the good work Dave! Soon Drift Away will be brand new! Kevin M/V AUtumn Dream

  3. If and when you get that south, Atlantic Yacht Basin is a good yard. James Taylor is a pretty straight shooter. Watch out for a Marine Electronics contractor he uses named "Kevin" (Just kidding) Todd Ayers tried to do a number on me, but I resisted and prevailed.
    AYB gives free dockage while they are working on your boat.
    The beauty of the internet... You can screw us, but you can't hide.