icer5160

iTrader: (4)

I wanted to create a quick guide on how to rebuild the OEM Mitsubishi Alternator. As many of you may know, aftermarket replacements tend to be unreliable. More often than not, these are poorly rebuilt/remanufactured units where the internal replacement parts are of sub-standard quality. They are also still fairly expensive, expect to spend around $250+ for a typical aftermarket unit. A brand new OEM unit costs over $500.

The benefits of rebuilding the unit yourself is primarily cost savings. For a few hours of your time, you can save hundreds. You can also ensure the quality of the replacement parts and workmanship is above board. This was my 1st time ever rebuilding an alternator, it was a fun learning experience while also saving some cash. I'm also a bit OCD about my Z and I want to keep items like this as original as possible.

In my case, the alternator bearings were in the early stages of failure. Symptoms were intermittent buzzing, I was able to confirm the alternator was the source using an automotive stethoscope. It's sometimes difficult to determine alternator noise from normal power steering pump noise (they are mounted next to each other). The charging system itself was working without issue, meaning the rectifier, stator coil, rotor, and voltage regulator/brushes were all in good working order. The process to remove/swap alternators is quite involved, so instead of rebuilding the unit already in my Z, I pulled the old one off my spare engine and rebuilt that one to minimize downtime. My old Z's alternator has 106k miles on it and was working perfectly up until my old Z met it's end. I could have slapped this unit in the vehicle as is, and been confident it would work. However, there's no telling how many more miles it would last, most likely the bearings would go soon.

Components to consider when Rebuilding an Alternator:
1) Bearings (common failure item)
2) Voltage Regulator/Brush Assembly (common failure item)
3) Rectifier/Diode pack (rare failure item, depends on conditions)
4) Slip Rings (rare failure item, depends on conditions)
5) Stator coil (should be tested with multimeter prior to rebuild)
6) Rotor (should be tested with multimeter prior to rebuild)

If you have a bad stator or rotor, the unit is essentially junk unless you can find a good/cheap replacement part (say from a junk yard!). The stator and rotor are the most expensive components of an alternator. It is rare when these components fail. It would take major debris or heat for one of these to break. Items worth replacing are bearings, voltage regulator/brushes, slip rings, and the diode pack. Depending on the running conditions of the alternator, it's also rare for the slip rings or diode pack to fail or wear out. It would take prolonged periods of non-ideal operating conditions such as exposure to a combination of mud, water, dust, and oil. Also extreme heat or salted roads. Note: There are plenty of guides/videos on YT covering alternator components, how they work, how to test them, etc. If you're interested in rebuilding an alternator, I highly recommend doing some homework on these before proceeding.

In my scenario, I ordered replacement bearings, voltage regulator/brushes, and slip-rings. I ordered the parts before tearing down the unit for a close inspection, but the parts are cheap enough that it's worth spending the extra cash (just in case). There are a few reputable online retailers who sell these parts. The vendor I chose was Maniac Electric Motors. Here's a LINK to the 350Z/Mitsubishi unit parts page. The listing says 03-06, but I assume this also covers 07-08 Z & Gs with the HR.

Rebuild Process...

Hit all the body bolts, screws, pulley nut, and stator band (center piece where aluminum casing attaches) with some WD40.

Front View - Notice 4x8mm perimeter bolts

Rear View

Side view

Crack and remove all the 8mm perimeter body bolts.

Grab a hammer, preferably a dead blow hammer to prevent marring the aluminum casing and start tapping against the front casing ears. The goal is to separate the rear bearing from the rear casing. The entire rotor and front casing should separate.

Casing separated, rotor with front case. Note: I removed the pulley 1st, but the rust kept the rotor with the front casing during separation, Note the rear shaft bearing with blue seals.

Once the rotor has been removed, you can proceed with removing the pulley & nut (24mm). I used a 3/8" impact with a conversion adapter to 1/2" since I don't have a 24mm 3/8 socket. With a little WD40 assistance, the nut broke free, but it did require some persistence. I highly recommend using a 1/2" cordless impact, the nut should zip right off without any trouble.

With the pulley removed, add some WD40 to the rotor shaft where it slides through the main bearing. If you're lucky a few light taps with a hammer will separate the rotor from the main bearing. In my case, I have an arbor press, so I used that instead. Some rust/corrosion had formed around the front shaft, gluing it in place. You do not need to press the new bearing onto the rotor, it's a slip fit (tight, but should slide right on).

Once the front case has been separated from the rotor, you need to remove the front bearing. The front bearing is captured by a plate with 4xScrews. Crack these loose, I was able to do it with a hand screw driver, no issue, but an impact would be a good idea. Once the capture plate has been removed, you can simply tap out the bearing with a hammer and socket. I used my press, but forgot to take pictures.

Removing the rear bearing from the rotor shaft is more of a challenge. Typical automotive pullers are too large, the claws can't fit in the gap to get a good bite. I had to be a little creative and used my ball joint separator. I added a small 4mm 1/4" socket to press against the shaft. This did the trick, very clean, no damage was done to the shaft or slip rings.

Home-brew bearing puller. Just a cheap Harbor Freight ball joint separator. Works great!

Bearing removed, I needed to add a longer socket/bit to get the last few mm of the bearing off.


With both bearings removed, you can move onto removing the stator from the rear casing. It's held in place by a 12mm nut from the rear battery post & 3 philips screws. Two of the screws are easy access, the 3rd one is half hidden by the stator coil itself. To safely gain access, you will need to loosen everything else up and slightly bend the stator coil assembly away from the casing. There is a cut-out on the casing to assist with access. Just be careful not to scratch or mar the surface of the copper coils/windings. There is a protective coating on the the copper wire which acts as an electrical insulator. Damaging this could ruin the entire stator!


Screws circled in yellow.


With the alternator mostly disassembled, you can start the cleaning process of all the pieces. I like to use gasoline and various brushes. To get the really caked on stuff, I use a fine steel bristle brush. Here's how the cleaned up parts came out.


Inside view of inner and outer casing.

All parts cleaned up. New replacement parts also shown.


I'll continue in more detail for Part II - Reassembly. My apologies for lack of detail on some steps. I'm short on time and will need to polish/edit the post later.
Cheers!
-Icer

dkmura

iTrader: (64)

Hey Icer- your thread was moved to the DIY section as it belongs there. The content is more advanced than most of the threads in the maintenance section.

Jynx

This is a great write up, thank you. My alternator has just started playing up, working fine when it's cold but failing to charge once it is upto temperature so I'm plannig to rebuild it for the reasons you've listed. I look forward to the next part of the guide. Great photos too!

Thanks,

Jynx