Tech: Installing the Mobi-Arc 90 Amp Stator in a Toyota Alternator Short Cuts

| Toyota Tech | Toyota Maintenance | Toyota Section |

By: Bill Morgan - 9/03.

One of the weaker points of Toyota truck charging systems is the alternator output. It's OK, it's very reliable, but doesn't have great output for a lot of accessories. With a winch, the charging system is put to the test just keeping the battery from falling on its face. And while you can weld with the stock alternator if you install a very efficient welding head-end like the MOBI-ARC unit, the 60 amp output sets a pretty low ceiling on the thickness of steel that may be welded. I don't have the funds for a full on-board welding system, but big tasks are accomplished by knocking down little tasks one at a time, and for $60 the MOBI-ARC 90 amp stator conversion kit seemed like a very good idea even if I stopped at that point.

The stock alternator, new stator, and new brush holder.

A quick call to Scott at MOBI-ARC gave me the information I needed. The upgrade kit is made for MOBI-ARC by a reputable stator manufacturer, and they resell it with very little markup (after all, they are in the welder business, and this just lowers the barrier to entry for an end user to buy one of their on-board welders). A few days after ordering, the kit was delivered to my door.

I have done a similar successful stator conversion on a motorcycle, and this kit looked like a comparable, very high quality kit. Scott included alternator brushes in a holder, and replacing these is a very good idea any time the alternator is disassembled. As it turns out, my fully functional good alternator was on its last leg at 160,000 miles, and would need the brushes - and more.

Removing the stock alternator on a 22RE

Removing the alternator from the truck is a sort of Rubic's Cube exercise. The Factory Service Manual (FSM) would have you remove the fan shroud and lower coolant hose. However, my coolant is not particularly well-trained, and I expected it would not stay put if I removed the hose. I put the job off for a while.

The new and old brush holders, close-up view in the right photo.

There was really no need. On my solid axle conversion truck, the alternator can be removed without taking off all that other stuff, if you hold your tongue just right. Take your time and work from below, and don't be in a hurry. First, DISCONNECT THE BATTERY. Unplug the control harness from the rear of the alternator, then gently move the rubber insulator from the charge wire and remove the nut and connector from the charge stud. Remove the pivot and adjustment bolts, and gently pry the alternator loose from its bracket. Begin the turning and 'slipping past stuff' exercise from below the truck, and you will be holding the intended victim in your hand.

A 1987 22RE alternator has a round plug in the back. Other years may have an oval plug, and may mount differently on the engine, so if you intend to obtain a junkyard alternator to modify, be sure it matches your alternator. Just a note - many of the internal parts are swappable between alternator styles, just another benefit of the Japanese engineering processes at Nippon-Denso and Toyota.

Disassembly of the stock alternator

Now begins the disassembly. The FSM is particularly helpful here. Unbolt the rear cover (3 nuts, and the charging stud nut and insulator) and gently slide it off. Unscrew the two Phillips screws holding the brush holder on the alternator, and gently wiggle it off. Inspect the slip-rings on the rotor for wear; mine was nearly shot, as were my brushes. Time to rob the trail spare for parts, a low mile late model alternator from, I think, a 3.4 V6 (engine left side but inverted, serpentine belt model at least).

Removing the stator connections to the diode board. A small gear puller can be used to open the case. Removing the case studs.

Remove the stator connections to the diode board (4 screws), remove the remaining screws holding the diode board and regulator to the case, and gently slide the diode board and regulator off the alternator. Using a small gear puller (NAPA has a decent one, configurable to 3 arms or 2 arms as needed), pull the case apart. Just a note, be sure the puller bolt pin is small enough to fit inside the insulator ring on the end of the rotor, or you will break it. I did, and fixed it with epoxy, but it would be nice to avoid that.

You will then be presented with the open alternator. To make the job easier, the pulley must be removed, which is easily accomplished with an air wrench and a vise holding the pulley (be sure to not damage the pulley in the vise jaws). Be sure to hold the alternator rotor while doing this, because once the pulley is off the rotor may fall free!

Upgrading the alternator with the Mobi-Arc components

Mark the alignment of the stator wires.

Remove the case studs from the case. Mark the location of the stator wires relative to the case. Now comes the fun part, not for the faint hearted, and likely the point of no return: support the front case on wood blocks, and using a skinny drift (punch), slip it between the cooling holes to the stator and gently tap it out of the case. Be patient and work your way around. Eventually you will have an empty case, marked with appropriate locations for the new stator wires. Place your new, 90 amp double-delta-wound stator on the case and gently tap it into place with a drift, avoiding at all costs any contact with the copper-colored wires! The insulating varnish is quite thin, and you do NOT want to scrape it and expose bare conductors. The steel core consists of layers of thin steel, so be careful with those too. The clearances within the housing fairly define close, and I was none too sure I had gotten the stator pressed in without damaging it. But as you will see, I was successful.

Carefully tap the stator in using a drift and hammer. Also, very carefully clearance the stator wire hole.

When the new stator is bottomed in the case, test fit the rear cover. I had to clearance the hole in the rear cover so one of the connector stake-ons would have no risk of contact. I also had to file a bit off of the connector to ease assembly. Make any wire bend adjustments carefully, and do NOT expose bare wire. Ensure that once the case is assembled that no wires contact metal, or come closer than you can help. Take your time at this point - you do not want to have to re-do a step.

With everything fitting correctly, install the rotor, case studs, and the rear case. I used a vise to gently squeeze one side of the case, and tapped the other side with a deadblow hammer until the case studs emerged and would accept the case nuts. Tighten the case nuts in a cross pattern until the case is closed.

Slip the rubber insulators on the connectors - I found dielectric compound (insulating electronic silicone grease) helpful especially on the larger, new connector. Install the diode board and regulator. Gently adjust the stator connectors until the holes line up, and screw them to the diode board. Continue reassembly until your newly rebuilt alternator gleams in your hands, waiting for the chance to add to your zapping needs.

Oh, and being the pessimist I am, I took it to NAPA to make sure it worked properly. It did indeed, putting out a strong 14.5 volts at about idle. You might want to do the same before you install it.

I am now the proud owner of a Nippon-Denso 90 Amp but otherwise stock and freshly rebuilt alternator. Not for the faint hearted or fat fingered, and a bit more subtle than pounding out wheel bearing races, but if you have some skill with delicate assemblies, it's well worth the effort. If you don't feel up to it... contact MOBI-ARC for an alternator already modified!

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