M20K Alternator Coupling

[Mike A]

I’m pretty sure I know the answer, but want to see if there is anything else I should check before I have the alternator pulled on my TSIO-360-LB - I went to go for a flight yesterday and the voltage never came up above 11.5. Checked all fuses, turned electronics on and off and nothing changed.

 

I’m assuming, as the post title implies, that I need to replace the alternator coupling. I have had voltage fluctuations before, but they normally went away after a few minutes which I understand is a telltale sign.  Did 5 hrs 2 weeks ago with no issues  

[Fly Boomer]

7 minutes ago, Mike A said:

I’m pretty sure I know the answer, but want to see if there is anything else I should check before I have the alternator pulled on my TSIO-360-LB - I went to go for a flight yesterday and the voltage never came up above 11.5. Checked all fuses, turned electronics on and off and nothing changed.

 

I’m assuming, as the post title implies, that I need to replace the alternator coupling. I have had voltage fluctuations before, but they normally went away after a few minutes which I understand is a telltale sign.  Did 5 hrs 2 weeks ago with no issues  

No delay -- that can lead to bad things.

[Steve Dawson]

Just replaced mine as well as installed a new alternator. The couplings are expensive and hard to find but I was lucky to find one at Aircraft Spruce. I'd suggest to get the alternator replaced or rebuilt when you have it off.  

[231LV]

It is absolutely your coupler...my voltage would start fine then slowly slide lower and lower as the coupler heats up and starts slipping. Finally, there was no voltage at all except what was coming off the battery. Get it replaced and have some happy, worry-free flights. If you haven't had the alternator rebuilt in a while, this would be a good time to get it done (or purchase a yellow-tagged unit).

[A64Pilot]

2 hours ago, Fly Boomer said:

No delay -- that can lead to bad things.

This, no truer words have ever been uttered. 

[Mike A]

37 minutes ago, A64Pilot said:

This, no truer words have ever been uttered. 

100%. Shut her down, pushed her back in the hangar, and drove instead. 

[jlunseth]

Well, the worst that can happen is that you have to fly without electricity. Drop the gear while you have electrical power (mind the gear extension speed) and switch the master off. You are now truly VFR while you fly to a safe place to land. You will find that the single battery in the 231 has practically no value as a backup, you might get a half hour out of it but then you have nothing for radios when you approach and land, you will be truly NORDO. Hopefully you are at stable cruise so you can just leave the engine settings alone until you reduce power for landing, you will not have panel instruments to tell you anything about temps. Not to say you should take off knowing you have a problem, but as emergencies go it is nothing like an engine out.

A few years ago I went through a number of couplers. They were coming from the same aftermarket source, although I don’t know for sure what that was (my A&P was buying them until he got disgusted). They would last for a trip or two and then fail. I want to say we went through four of them in the pace of roughly a year. We finally went direct to Mooney and bought one. It was much more expensive in the short run, but lasted five or six years until engine replacement, so much less expensive in the long run. 

[A64Pilot]

15 minutes ago, jlunseth said:

Well, the worst that can happen is that you have to fly without electricity. 

Maybe not, I’ll post a couple but everyone can Google but you get the idea, you can have the shaft shear and the whole gear is loose inside of the gear case, if that happens your lucky if you just have to buy an engine

http://www.aero-news.net/index.cfm?do=main.textpost&id=7cd2ca0a-3570-48bb-8022-1cd45e0cfcda

https://hartzell.aero/tech-tip-alternator-drive-couplings-careful-installation-required/

[Phil EF]

Happened to mine last month. (GB)
Worn brush was the cause. 

[jlunseth]

The failure mode in those articles is a different issue from a coupler that has been in an engine for a few years, then failing. Believe me, I know. One of the couplers I had to install was put in by a non-Mooney shop. The coupler is held on the shaft by a tiny cotter pin at the outboard end of the shaft. The small cotter pin can be used because there is a bushing inside the coupler that keeps it running concentrically on the shaft and therefore no vibration or chatter. The shop that installed mine did not put the bushing in, and its absence is not visible on inspection. That allowed the coupler to rotate off-center and hammer the tiny cotter pin to death, with the result that the pieces of cotter pin and the coupler fell off into the running engine. I was lucky, there was no damage and all pieces and parts were accounted for in the sump. But as I said, those articles are talking about a different issue from the one where the charging amperage does not come up until after the engine warms some. That means the rubber coupler lining, which serves as a clutch, is wearing past tolerance and and the assembly needs to be replaced. The “warm-up” phenomenon is particularly prone to happen in late fall/winter when the temps start to get cold. It is certainly true that careful install by a knowledgeable Mooney shop that has the repair manual in hand is necessary. 

However, the failure mode where the coupler assembly departs the shaft does not show pre-departure symptoms, not in my experience. The assembly of the coupler to the shaft suffers sudden failure and the coupler assembly departs the shaft. You won’t get intermittent charging and then no charging, you just get no charging period. Then it is a matter of luck whether the departed parts cause damage in the running engine or not.

As long as the coupler is in place the engine will not suffer damage because that is what the coupler is there for - if the alternator freezes for some reason the rubber liner lets go its grip on the drive shaft and the alternator no longer functions but the engine is not damaged.

The coupler needs to be installed by a competent Mooney mechanic who has the repair book in hand. 

I kept that coupler assembly for several years so I could take pictures and people could see. Have since tossed it. 

Edited August 24, 2023 by jlunseth

[GeeBee]

Not quite. A failure may result in the coupler protecting the engine, however, a coupler slipping can generate lots of heat, cause disintegration of the rubber into pieces which then gets circulated in the engine oil. This is why even with a backup alternator, a failed alternator is listed in emergency procedures as 

"Terminate Flight As Soon As Practicable"

[Mike A]

So as I’m waiting for the mechanic at my hangar I have the top cowling off and can see that when i turn the prop the shaft to the alternator also turns. Would this be the case with a coupling failure or do I need to think about overall alternator failure or electrical issue somewhere?

[Fly Boomer]

9 minutes ago, Mike A said:

So as I’m waiting for the mechanic at my hangar I have the top cowling off and can see that when i turn the prop the shaft to the alternator also turns. Would this be the case with a coupling failure or do I need to think about overall alternator failure or electrical issue somewhere?

Possibly "failing" but not completely blown up yet?

[GeeBee]

Possibly slipping or bad internals. You need a diagnostician. 

[A64Pilot]

4 hours ago, Mike A said:

So as I’m waiting for the mechanic at my hangar I have the top cowling off and can see that when i turn the prop the shaft to the alternator also turns. Would this be the case with a coupling failure or do I need to think about overall alternator failure or electrical issue somewhere?

It’s going to turn because there is no load, you have to remove the alternator regardless of the problem.

The installation procedure for the coupling from memory has a torque check to see when it slips, I take it to someone myself as I don’t have the tooling to do the job.

Its like Mags, I’m legal to do Mags, but prefer to send it out to a specialist.

If the coupling isn’t close to new you ought to replace it, some do so every 500 hours.

It would be prudent to do as was said earlier, to send it in for inspection / repair depending on if you can wait, cause it’s not going to be done in a hurry.

Either way if you suspect the coupling I think I’d cut the oil filter and look for orange rubber pieces

I’ve only watched enough of this video to know that it shows the torque check procedure to see if the coupling is slipping or not, but suspect it’s a pretty good video considering the source.

It’s also very important that the cotter pin be installed exactly in accordance with the instructions, it’s not a normal cotter pin installation, if done the normal way it can hit something in the engine and cause damage.

This isn’t hard, just need the special tools and read and follow directions and it will be fine

[jlunseth]

7 hours ago, Mike A said:

So as I’m waiting for the mechanic at my hangar I have the top cowling off and can see that when i turn the prop the shaft to the alternator also turns. Would this be the case with a coupling failure or do I need to think about overall alternator failure or electrical issue somewhere?

I don’t think that tells you anything. It means that there is some grip of the drive shaft by the coupler, but the forces at work when the engine is running are quite a bit greater than when you turn the prop by hand. 

Worth saying that there are other things that many other things that could cause there to be no charge, alternator, voltage regulator, even a loose wire. The coupler failure is a known issue with the 231 however.

I watched the video that A64 put up. I don’t recognize that as a 231 coupler assembly. It may be a different style of coupler specifically for Plane Power alternators, I don’t know, but among other things the bushing I mentioned is not present. The install is not complicated. Have a good Mooney A&P do the install if a coupler is what you need.

[philiplane]

8 hours ago, Mike A said:

So as I’m waiting for the mechanic at my hangar I have the top cowling off and can see that when i turn the prop the shaft to the alternator also turns. Would this be the case with a coupling failure or do I need to think about overall alternator failure or electrical issue somewhere?

you an use a large screwdriver to engage the alternator fan blade, and gently try to turn the prop. If it the engine won't turn, the coupling is good. If you can turn the engine with zero resistance, the coupling is bad. If you have significant resistance while turning, the slip feature is working, and the coupler is good.

[kortopates]

I don’t think that tells you anything. It means that there is some grip of the drive shaft by the coupler, but the forces at work when the engine is running are quite a bit greater than when you turn the prop by hand. 
Worth saying that there are other things that many other things that could cause there to be no charge, alternator, voltage regulator, even a loose wire. The coupler failure is a known issue with the 231 however.
I watched the video that A64 put up. I don’t recognize that as a 231 coupler assembly. It may be a different style of coupler specifically for Plane Power alternators, I don’t know, but among other things the bushing I mentioned is not present. The install is not complicated. Have a good Mooney A&P do the install if a coupler is what you need.

You are correct. The video is for the Permold case, such as the 550’s, which is a different coupler than the ones used in the 360’s.
It’s also the 550’s that suffered from incorrect installation issues - not so much the 360’s.


Sent from my iPhone using Tapatalk

[Fly Boomer]

15 hours ago, jlunseth said:

I watched the video that A64 put up. I don’t recognize that as a 231 coupler assembly. It may be a different style of coupler specifically for Plane Power alternators, I don’t know, but among other things the bushing I mentioned is not present. The install is not complicated. Have a good Mooney A&P do the install if a coupler is what you need.

I almost certainly know less than anybody else here, but I think that the "permold" engines are only big-bore Continentals, which would leave out the engine in a 231.  Actually, I have only seen "permold" associated with 520s and 550s so it may be more specific than just "big-bore".

EDIT:  I see I'm 20 minutes late.  @kortopates got here first.

[A64Pilot]

I’m pretty sure but not certain that ALL Continental alternator couplings have issues that can cause severe engine damage.

Even the little old A and C series engines but those are just cushion drives, no slipping. Those are simple just replace two little rubber bits

The 520 I had had the best of all possible alternator drive set ups, in my opinion. It was belt drive, but off of the back of the engine, so to change the belt it was as simple as a car, no prop removal required.

[Fly Boomer]

2 minutes ago, A64Pilot said:

The 520 I had had the best of all possible alternator drive set ups, in my opinion. It was belt drive, but off of the back of the engine, so to change the belt it was as simple as a car, no prop removal required.

I'm pretty sure that wasn't a permold 520.

[A64Pilot]

17 hours ago, Fly Boomer said:

I'm pretty sure that wasn't a permold 520.

Other than apparently that is what the video covers, I don’t know where the concern of permold came from.

The issue is that ALL Continental alternator gear drives if not properly maintained to include periodic replacement can cause engine damage, period. Even the 1940’s A &C series engines, and so far as I know I believe ALL gear drive alternator couplings should at least be removed and inspected on a 500 hour interval, but don’t take that as a requirement, I don’t believe there is an AD.

They aren’t something to take lightly.

I just threw out the IO-520 that was in the 210 because I quite liked its design, seemed to be the best of both worlds is all.

Really if you don’t believe the continental IO-360 alternator drive can cause engine damage Just google it. 

I think of it like the 500 Mag check, no big deal as long as you have it done on schedule, but if you have an engine that you have no idea when or of the alternator drive coupling was replace, you might want to consider doing so.

There are a few different SB’s it seems, one for the little guys which this one is

https://www.qaa.com/wp-content/uploads/SB95-3B-1.pdf

There are apparently a couple for the big motors too.

But the only point I was trying to make is don’t take the likelyhood of a slipping / failing alternator coupling lightly, it’s not one of those things that you should defer.

[A64Pilot]

This article I think covers it better than I can, and perhaps it’s more believable than just some internet guy that for all you know isn’t even a pilot, much less a mechanic

https://www.aopa.org/news-and-media/all-news/2022/august/10/aircraft-maintenance-critical-knowledge-about-alternator-couplings

[takair]

3 hours ago, Jack Russell said:

So let’s say hypothetically speaking say that the alternator was a bit slow to start charging after start up but then one day charging ceased altogether. Alternator removed and sent to a specialist for inspection. 500 hour inspection carried out, new coupling fitted, all working fine for 10 hours or so until charging ceased for a couple of minutes in flight but then came back for remainder of flight. All OK on next flight too. Next flight all normal at first but then low volts light and no charging at all. Filter pulled, lots of orange particles in the filter but no metal.. On the one hand maybe dodged a bullet? On the other what to do now? Would that necessarily mean a tear down?

There are lots of discussions on this on the various forums (here and Beechtalk). One concern is the particles plugging the oil passages and not getting oil to the right spots.  I don’t know how to prove or disprove this.  The alignment of the gears is critical.  Not easy, but you can check the gear mesh pattern by looking at the gears.  Did you get 500 hours out of the first one or did it start after  a recent overhaul?  

[GeeBee]

I would say the filter did its job.

Personally if it were me, I would:

Have the oil cooler flushed

Do a couple of runs, with new oil and filter of about 5 hours or less

If the results are clear do at least two 25 hour oil analysis and if all was good continue on. 

I am not an A&P but I did stay at a Holiday Inn Express last night.