The Stock Alternator
Many boats, specifically sailboats, come equipped or have have used the 5" case Motorola/Prestolite/Leece-Neville style alternator over the years of production.
This case style alternator today is built by Leece-Neville. They are specifically marinized for ignition protection and are called the 8MR series or marine series. They are available many outputs from 37 to 105 amps and in a 2" single foot, 1" single foot, and single ear and triple ear configurations. The regulators though are all the same design.
The regulators that comes stock on most new 8MR series alternators are voltage adjustable but still only single stage not a three stage regulator thus lacking temp sensing and float modes. According to Leece-Neville tech support this regulator has an adjustable output range from 13.8 - 14.6 V. It ships from the factory set at 14.2V.
This article will show you how to convert a Motorola/Leece-Neville style alternator to external regulation. Once you have done this conversion you can then use a Balmar, Ample Power or other external three stage regulator.
This particular alternator is a 90 amp Leece-Neville 8MR2070TA with a 1" foot and triple adjusting ears. It fits many Universal and Westerbeke engines as well as many others.
Remove Thee Four Screws
The first step in this conversion is to remove the four machine screws holding the regulator onto the alternator. They've been loosened so it's easy to see which ones they are.
Flip The Regulator Over
The next step is to remove the four wires that connect the regulator to the alternator. this is as easy and straight forward as it sounds.
Once the wires are disconnected simply tilt the regulator up to expose the internal brush connections. You'll need a set of needle nose pliers to pull the connectors off the brushes. This is quite simple and takes about 20-30 seconds to do.
Spark Arrestor Gasket
Aside from the epoxy coated finish and general marine construction of the 8MR series this gasket is what makes it USCG compliant and ignition protected. It prevents errant sparks from the brushes from igniting any potential fumes. With most diesels this is not really a huge concern but it's still a good idea to re-use this gasket upon reassembly.
The Conversion Kit
Leece-Neville is nice enough to make an external regulation conversion kit for this series of alternator. It should be available from just about any Leece-Neville dealer.
I ordered this conversion kit from my local alternator shop who is a Leece-Neville/Prestolite dealer. The total price for this 90 amp marine rated alternator with the conversion kit was about $325.00. About half the price of the Balmar Series 81 (which is now discontinued).
Please be careful when buying on-line as there are numerous Chinese made clones of these alternators. They are not nearly as well built nor as robust.
What's In The Box
The conversion kit comes with everything you'll need, including the wires, bolts and insulators, to make this a simple conversion.
The first step in assembling the kit is to slide the ring end of the wires over the carriage bolts as shown here.
In this step you slide the black plastic insulators over the carriage bolts with the flat side facing the ring and the side with the smaller square facing up as shown.
Because voltage is running through these wires they must be installed and insulated correctly so they don't ground out on the aluminum plate. In this picture the small square is properly oriented to prevent the bolt from making contact with the cover plate and will be properly insulated.
Back Side View
Here's what it looks like from the back.
Add The External Insulators
With both bolts and internal insulators installed place the large insulating washers over the bolts. Next drop the two small washers supplied on top of the insulators, add the nuts and tighten them down.
Here's the view from inside the cover plate with everything torqued down and tight.
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