500 hour alternator inspection

[Matt Ward]

In 2004, about 1200 tach hours ago, my 1966 M20E had a factory overhaul of the IO-360-A1A. As part of that, a new alternator was installed, an interav 015-01237. I’ve been flying the plane and the alternator seems to be working as evidenced by my JPI EDM 700 showing a consistent 14v. During run up, I try to get a jump on the ammeter with lights and usually can detect a slight deflection. My new A&P is telling me to do a 500 hr inspection of the alternator as part of my first annual. Does these seem customary to you guys? I typically thought of alternators as needing to display some sort of adverse conditions before a major service event but maybe I’m just naive. What do you guys think? Anything else I can do before agreeing to the 500 or is this standard procedure? Thanks!

[carusoam]

Sounds like your mechanic knows his stuff...

He is offering to do some things that I could wait on...

Depends on how you are going to use your plane...

Do you fly in IMC?

Do you only have one alternator?

Do you have a second battery installed and ready to go when the first one is drained?

I flew my M20C until it’s generator croaked... then got a new one... no IMC for me at the time...

I was 50miles from home when my only battery drained out... that’s how I knew the generator stopped working... 

Ask your mechanic what is involved in the 500hr inspection... then make the decision... see if you can find it on line...I’m not familiar with that one...

PP methods of risk avoidance..., not a mechanic...

Best regards,

-a-

[Matt Ward]

Marginal amount of IMC. Honestly try to avoid it but will punch through a fog layer to get on top! But 95% VFR for sure. Only one of everything. 
thanks for your feedback @carusoam sounds like your take is similar to mine...good to do, but maybe wait on some of it. 

[carusoam]

Good mechanics know tons of details about planes... 

They often offer every service you may be interested in...

Often, you get to set the limits, to keep from having your plane getting turned into a brand new ship...

Some people enjoy the opportunity of turning an old ship into a brand new one...

 

One way to separate out the work being offered... Is it an air worthiness requirement, or something I should consider for other reasons..?

Often mechanic’s know the work being done today will save a huge chunk for you down the road...

Good to get to know your mechanic! 

Best regards,

-a-

[Matt Ward]

Wouldn’t brushes and bearings be a part of a typical Mooney annual? The MM I have just says “inspect” the alternator so honestly I don’t know what all a 500 entails besides pulling the part off the plane. Is that documented somewhere I can find it? Thanks!

[carusoam]

There is a 100hr inspection list... around here somewhere...

Very similar to an annual check list...

That makes for some good reading...

Alternators don’t usually have such short life spans...

Vac pumps do...  Often 500 hours and out... depending on your use...  (I have a pair)

Mags have a 500hr inspection/OH that people like to stay on top of...

wait some time and check back often... see if anyone adds some detail...

Often, somebody is hoping the alternator croaks, just to update with a better lighter version... 

Best regards,

-a-

[Matt Ward]

Thanks for all your help @carusoam you’re really a value around here to folks with questions. If you ever get out to CO, I owe you a beer and a ride in my E!

[Guest]

23 minutes ago, Matt Ward said:

Wouldn’t brushes and bearings be a part of a typical Mooney annual? The MM I have just says “inspect” the alternator so honestly I don’t know what all a 500 entails besides pulling the part off the plane. Is that documented somewhere I can find it? Thanks!

On old generators and Prestolite alternators checking the brushes is quite simple, checking the bearings involves loosening the drive belt to then spin the pulley to feel and listen to the bearings.  Both are simple and good maintenance practices. Brushes are real actively cheap, “fly to failure” is an option if you know when failure will happen.  Many other alternators are not quite as simple to check/maintain.

The Interav alternator is reputed to be robust but still needs some basic checking, I’m not sure how easily though.  I believe that Quality Aircraft Accessories now produces/supports them.

Clarence 

Edited April 18, 2020 by M20Doc

[Matt Ward]

Thanks @M20Doc  QAA does them now. Any insight into how to identify a near end of life interav? I would like to stay on top of it with basic, routine maintenance but also wouldn’t mind upgrading it when it’s time to go.

[ArtVandelay]

I found this:

https://www.aopa.org/news-and-media/all-news/2018/june/20/aircraft-maintenance-alternator-inspections

But I disagree with it, if I was worried about it, I would buy brushes and stick them in my spare parts bag.

[Matt Ward]

Thanks I saw that too. I appreciate your help!

[carusoam]

As a partner to the alternator....

There is a voltage controller akaVR to be aware of too...

To at least know what model you have...

The original may have been the sticks and stones and springs model...

My sticks,stones,springs stuck in charge mode (?)... and melted the solder out of my generator...

Zeftronics is the big name in voltage regulators around here...  it also can have remote lights to give a hint of how well your VR is working electronically...(not mechanically)

One of the most common failures we see on MS... the ‘field’ wire breaks and the alternator stops charging...

Bouncing wires are best tied down / supported... they can harden up, and break over time...

 

Back in the day... alternator belts had a tendency to break down... belts haven’t rotted off the front of engines in decades...

Setting belt tension is important... if your alternator is in good condition and not charging... it is quite possible That it slips under certain conditions... there is a procedure for setting and checking the tension...

PP thoughts only, not a mechanic...

Best regards,

-a-

[MB65E]

If you are worried about the alternator failing then pull it off now. It’s cheaper to fix in the hangar now than an AOG trip to Elpaso. I have never had an alternator last 1200hrs on an airplane. A simple inspection now will give piece of mind. 
14v sounds acceptable. I have also changed way more batteries directly after I’ve replaced alternators than I care to admit. Aka, was not the alternator. I’ve also had bad batteries damage alternators too. 
Your guy is not wrong. Any maintainer that wants to pull an alternator is doing you a favor as it’s absolutely no fun to change on a vintage bird. 
-Matt

[Andy95W]

It sounds like your Interav alternator is working just fine.  I wouldn't touch it until it starts giving you a reason.

And in 20+ years of working on small airplanes I've never heard of a 500 hour inspection of an alternator.

[cliffy]

I have an InterAv alternator on my Mooney   22+ years. Failed once and we overhauled it Brushes were way worn out. New parts from InterAv in those days, Brushes and bearings. Diodes were all OK The slip rings for the brushes were another issue. they were way worn with about 1400 Hrs  IIRC. Had to turn the slip rings in a lathe to clean them up.   Worked perfectly for many years until engine overhaul at which time I put on a new one. Still going strong after 800+ hrs since  new engine. 

Might not be a bad idea to look at it now as its been 16 years. Just be prepared to buy a new one if it looks like crap when it comes off. Another item to look at is the mount that it goes on and that bolts to the engine case. A lot of them crack at the bolt holes. There are MANY different Alternator mounts for 4 banger Lycs.  Finding the right one can be a challenge. 

Do some thinking about the drive belt at this time also if you remove and replace the alternator. You gotta remove the prop to change it!

Things can snowball in a hurry once you get into it.    Maybe not waking sleeping dogs is an option.  Some people do subscribe to _ "if it ain't broke don't fix it" 

No one can tell you what's right for you  Your choice of many options. Welcome to airplane ownership

[Tim Jodice]

I have seen 500 hour inspections on front mount gear driven continental because failure of the alternator might also dump its guts in the engine and even if it doesn't stop running it likely did substantial damage. Not that anyone wants an alternator failure but at least belt driven failure even catastrophic ones dont harm the engine.

If he is willing to do it and it is not a lot of money I would do it for piece of mind. 

Somewhat off topic. I needed to replace my battery last year and when I was shopping for one the nerd in me couldn't just buy a battery but i had to read all of the specs. I found the Concorde RG35AXC rocks. Because batteries degrade I used 80% of reserve power. I found if you do go down to minimum equipment the battery would likely last longer than your fuel. 

Not suggesting to over look your alternator but having a great not just ok battery is good insurance. 

[Guest]

6 hours ago, Andy95W said:

It sounds like your Interav alternator is working just fine.  I wouldn't touch it until it starts giving you a reason.

And in 20+ years of working on small airplanes I've never heard of a 500 hour inspection of an alternator.

If his maintainer has Cessna experience, it likey comes from there.  It’s on many Cessna inspection checklists.  Cessna used alternators built on a Ford design, they had to be removed and disassembled to check the brushes.  Piper Cherokee’s used Chrysler alternators, like the Prestolite, the brushes are easily removed.

Clarence

Edited April 18, 2020 by M20Doc

[Matt Ward]

Thanks everybody for the feedback; this site is amazing!  I tend to fall into the "let sleeping dogs lie" camp as I've been alarmed by reading some of Mike Busch's "after repair incidents" too.  For now, is there anything you'd recommend to diligently keep an eye to try and spot deterioration of the alternator?  I keep a good eye on the JPI and make sure it's 14v in flight.  What else could I be doing?  Anything in preflight besides checking the tension on the belt?  And related, is there anything to do in order to try to avoid the dreaded AOG incident if it does fail on a cross country?  It seems extreme, but would it be the kind of thing to keep an extra one (they sale for about $450 from QAA) in the luggage area?

[philiplane]

The Inter Av is simply a Motorola 8AL series alternator.  They were made under the Leece Neville, Motorola, and Prestolite brand names. The only difference between the aviation and automotive versions is the external fan. There is no 500 hour inspection on them, he may be thinking of gear drive alternators on large Continental engines. 

That said, brushes are recommended every 1000 hours. They are cheap, and the alternator doesn't even have to come off the engine to do them. Brushes are #103-15.

Motorola ServiceManual.pdf

Edited April 18, 2020 by philiplane

[carusoam]

Looking at the JPI is nice...

Realistically, to see things happening/wearing in real time is near impossible... while flying a plane...

Download the JPI data to see what it has been doing over large swaths of time...

 

Will you be able to be part of the first annual?

This is where you learn the second most about your plane...

The second annual, you learn about all the things you decided on at the first annual... 

Its an iterative process that you get better at as time goes on...

Best regards,

-a-

[Scott.N]

On 4/17/2020 at 9:41 PM, Andy95W said:

It sounds like your Interav alternator is working just fine.  I wouldn't touch it until it starts giving you a reason.

And in 20+ years of working on small airplanes I've never heard of a 500 hour inspection of an alternator.

In 30+ years of working in an aircraft engine overhaul shop I've had access to Plane Power (previously Hartzell,  Electrosystems, Ford, and Prestolite) alternator and starter manuals and they've mentioned 500 hour alternator inspection procedures for at least the last 20 years.

This isn't just limited to gear drive Continental alternators. It also includes many of the belt drive alternators on Continentals and Lycomings as well.

Usually the lightweight alternators aren't field serviceable, but that older stuff still is.

Scott @ Pro Aero Aviation

[cliffy]

On 4/18/2020 at 8:27 AM, philiplane said:

The Inter Av is simply a Motorola 8AL series alternator.  They were made under the Leece Neville, Motorola, and Prestolite brand names. The only difference between the aviation and automotive versions is the external fan.

Did anyone ever take notice that the fan turns "the wrong way" and draws air from behind the Alt to the front for cooling?

I talked to an InterAV engineer about this years ago and he said they couldn't get good cooling of the diode bridge by blowing through the alt into the engine cowl so they had to suck it out against the normal flow of engine cooling air. 

[rbridges]

I just had my alternator replaced. As an owner, I'm a little aggravated. I've owned my plane for 10 years and have had 4 different people do my annuals. Never was it mentioned to inspect the alternator. By the time it failed, the brushes were worn to the point where the slip ring was ruined.  Not only that but I had to scrub a flight. Fortunately I was at my airport when it happened.  After I started googling, I saw that a 500hr inspection is recommended. Lesson learned, but not everyone is savvy on maintenance. I try to stay on top of things, but I do lean on the mechanics, maybe more than I should.  To answer the OP's question from last year, definitely keep an eye on your alternator. 

[PT20J]

I'm not saying that it's a bad idea. But everyone seems to say that most of them are repurposed automotive alternators. I have owned a lot of automobiles, mostly driven commuting to work in traffic, and most with around 120K miles on them when I got rid of them. At an average 30 mph, that would be 4,000 hours. I've never had a car alternator fail, or had one need service.

Skip

[A64Pilot]

21 hours ago, cliffy said:

Did anyone ever take notice that the fan turns "the wrong way" and draws air from behind the Alt to the front for cooling?

I talked to an InterAV engineer about this years ago and he said they couldn't get good cooling of the diode bridge by blowing through the alt into the engine cowl so they had to suck it out against the normal flow of engine cooling air. 

Often automotive designs have two fans, one on each end and the air is exhausted through the middle of the alternator, but the back fan is the important one as it’s cooling the diode pack.

But your tech is correct, the diodes create more heat than anything else, some non aircraft designs remote mount the diodes so they can get more power from an alternator.

I woud say it’s a safe thing to say that an alternator should last longer than the engine it’s on, some with more money than me replace all accessories at overhaul, and never get stranded with a bad alternator or starter.

‘However one that has brushes replaced before they are completely worn and bearings when they begin to show wear, well ought to last pretty much forever.

Brushes are a lot like brake pads, if you change them when they are half gone, the discs and slip rings last for a very long time.