68 M20G Alternator

[Nokomis449]

On my next-to-last last flight, my charging system went south on me.  A visual check of wiring, etc. showed no visible anomalies.  I removed the battery, charged it up, and it seems fine. Started the engine and voltage went down to 12.6 when it's normally 13.4ish.  On the 3 hr VFR flight home with radios and unnecessary electronics off (transponder and intercom on), voltage was at 12.1 when we landed.  I removed the alternator per A&P and have it in my hand.  It's a Prestolite ALY 8420, which is a 60A alternator.  According to Aircraft Spruce and other Google searches the G model should have the ALX 8521, which is a 70A alternator.  So are they interchangeable?  I see where some of the older Mooneys with the same O-360 engine use the ALY 8420 and it's on the Lycoming list for the O-360, but I can't find online where the G calls for it.  I've never had it off since I've owned it, so this is a new puzzle.  If mine is bad, do I replace it with the ALX 8521 70A, or stick with the ALY 8420 60A?  For the price difference, I'd rather have the extra amps.  I'll discuss this later with the A&P, but also want opinions from here.

And if mine is bad, what's the best route for replacement?  Who's got the best prices?  I need to be back in the air in 10 days so sending it out for rebuild may not be an option.

Thanks!

[carusoam]

Two things that come up regarding old charging systems....

What voltage regulator are you using?

how is the wire that connects the VR to the alternator?

The alternators themselves aren't known for croaking.

there are a few threads on the preferred alternators that are available.  Mostly because they are lighter weight...

For modern VRs, look up Zeftronics.

PP thoughts only, not a mechanic...

Best regards,

-a-

Edited March 7, 2017 by carusoam

[Nokomis449]

It's a ZEFTRONICS R15300 alternator control.  When the master is switched on, the light is green on the R15300 but I haven't checked the color with the engine running.  That's my next component to check if the alternator tests good.

EDIT:  I haven't checked every inch of the wiring, but a visual check of the terminals and easily-seen areas showed nothing of interest.

Edited March 7, 2017 by Nokomis449

[Yetti]

PRetty much need to check and redo all the wiring to the alternator.   When I pulled mine to do the starter, the B+ main battery charging big wire, the terminal came off in my hand.  The other wires should all be considered suspect.  There is alot of vibration.

You should be able to run the alternator to the auto parts house and have them test it on their test stand.

Jet driven has thread on how to find and replace the diode pack that usually is the culprit for going bad.

[carusoam]

Sounds like you need your mechanic to check to see if the alternator is producing voltage.  If it is, why it isn't making it all the way out to the battery...

Other than the green light, Does your Zeftronics have status lights on it? It way give some hints about what isn't right...

Best regards,

-a-

[mooniac15u]

When a diode fails you tend to get a lot of alternator noise but not a sudden total loss of alternator output.  Wiring is certainly a good place to start but on the alternator itself the first thing to check is probably the brushes.

[Nokomis449]

2 minutes ago, Yetti said:

You should be able to run the alternator to the auto parts house and have them test it on their test stand.

I took it to one of the big box stores last night, but the kids working the counter couldn't find "ALY 8420" in the computerized tester, so they couldn't test it. Today I'm going to find an old NAPA or mom n pop auto parts store that'll know what they're doing.

[Nokomis449]

UPDATE:

Just had it tested and the alternator is bad.  So now the decision: Rebuilt it, buy a reman, or buy new.  And if reman or new, which version?

[mooniac15u]

7 minutes ago, Nokomis449 said:

UPDATE:

Just had it tested and the alternator is bad.  So now the decision: Rebuilt it, buy a reman, or buy new.  And if reman or new, which version?

What does "bad" mean?

[Nokomis449]

I believe the words were "there's no output" or "there's nothing coming out of it" or some such.

 

[jetdriven]

The ALX alternators are basically a ford prestolite alternator. Any alternator shop should be able to replace the brushes, bearings, and diode pack.  Tell them its for an airboat.  75$ is a lot better than 600$ for a Kewlly overhaul, you have a half chance the new one wont work either.

 

 

[mooniac15u]

5 minutes ago, Nokomis449 said:

I believe the words were "there's no output" or "there's nothing coming out of it" or some such.

 

I assume you are working with an A&P on this project.  Have they checked the brushes?

[Nokomis449]

Yes, A&P/IA.  Was just told the brushes are bad (worn out, not making contact; made contact briefly after reassembly and alternator worked for a few spins) Bearing is questionable. This is the 2nd time I've owned this plane since 2005 and I don't recall the alternator ever being worked on or replaced, so it's probably got > 2,000 hours on it.  After discussion and considering this is a forever plane/IFR/night platform for me, I'm going with a new or reman alternator.  

[N201MKTurbo]

There used to be an old guy at the airport who fixed alternators, starters and mags. He would rebuild one of those for $200. Sadly he retired. 

IMHO  a good rebuild is as good as new.

[jetdriven]

If replacing, I would strongly consider going with the Plane Power alternator. Its new, and its of a much more modern design. Its 1990s Japanese vs 1960s USA tech. They are shipped from the manufacturer instead of Kelly in Alabama. After dealing with them over an alternator I'd feel better about one-tooth bob from the redneck alternator shop.

Edited March 7, 2017 by jetdriven

[Nokomis449]

16 minutes ago, bluehighwayflyer said:

I have a new ALY8420 with an 8130 on my spares shelf that I will sell you cheaper than you can get it anywhere else if you decide to go that route. PM me if interested.

Jim

Can't beat that... give me 24 hours to search & discuss with IA.. If we decide new ALY 8420, I'll take it.  I assume it's a Prestolite?  They all seem to sport the same model number.  I'm getting reman prices in the $500's... may go that route.  Also still trying to find out why all the sites say my G takes the ALX 8521...

[Yetti]

type data sheet has several model alternators for the G model.    http://www.67m20e.com/Mooney TCDS 2A3 Rev 52 dtd 9DEC10.pdf

 

301........ Generators and Alternators(a)

Generator, 50 amp, Delco-Remy, 1101915.................................................. 16.6lbs. ................... -24.5

(b)

Alternator, 60 amp, Prestolite, ALY8420, ALY8403,

ALY6420 or ALY8420M ............................................................................10.3 lbs. ................... -24.5

(c)

Alternator, 70 amp, Prestolite, ALX8403.................................................... 10.3lbs. ................... -24.5

Edited March 7, 2017 by Yetti

[Nokomis449]

I may have figured out the ALY-8420 vs ALX-8521 confusion.  Online sources (Aircraft Spruce, etc.) say the M-20G has an O-360A1A engine, but the engine logbook for my Factory Reman engine that was installed in 2002 says it's a -A1D engine.  According to Aircraft Spruce, the ALY-8420 fits the -A1D engine.  (Hopefully) problem solved.  I'll stick with the ALY-8420.

bluehighwayflyer, I sent you a PM.

[carusoam]

Since you are tying up all the loose ends....

My C's engine was the O360-A1D.  It had the Delco generator... and the heavy starter...

The letters after the dash often represent the other details that are attached to the engine... types of mags, and things on the accessory panel...

Does the -A1D stand for the generator? Or anything like that?

The weight of the generator compared to the light weight alternator is a huge difference for WnB calcs...

A forever plane also deserves updated dog house seals around the alternator and starter....

Best regards,

-a-

Edited March 8, 2017 by carusoam

[Guest]

This might help explain Lycoming engine models.

http://www.meyette.us/LycomingEngineNumbers.htm