I mentioned in another thread a few days ago that upon competing Annual Inspection on my plane, having subsequently had my oil cooler ‘overhauled’ (cleaned) and then doing a run-up to check for oil leaks, I’d found the charging system on my Lycoming O-320 was suddenly not working. This has been resolved and the solution now found provides an opportunity to document how personal involvement in maintenance and repairs can make owning a plane a whole lot less costly.
With the concurrence of the A&P IA who did my Annual (i.e. to work under his supervision) I first looked for airframe wiring that had been disturbed during the inspection, my first guess as to the cause of the charging problem, and found nothing. I then checked for a bad voltage regulator and over voltage control by parts swapping using spare units I happened to have on hand, but this made no difference. I then removed the engine cowling that I’d just replaced and did the ‘feeler gauge trick’ to perform a crude check on whether the alternator field coil could be energized. I should have done this first because holding a thin piece of steel near the front pulley bolt gave no indication of a magnetic field on the rotor. So then I checked for 12V-ish supply on the field coil wires, and that was fine. That lead to removing the field coil wires and checking for rotor continuity – there was none, so now after a very limited amount of work I was homing in on the problem. This is not rocket science to do…
The alternator then came off the engine, another 15 minutes effort, after which I looked it over and cleaned it while pondering my next move. It only has 200 hrs so looks like new, making me more determined that the fault might be something simple.
This unit is the traditional Prestolite-design 40 Amp unit used on Lycomings (now available from Hartzell) and it’s a very straightforward thing. However complete alternator disassembly (it’s detectably and semi-permanently safety wired) voids the $200 core charge credit if I needed a new unit so I decided to take a look at the brush block first, which comes out easily. This fairly quickly revealed that the connection between one brush and its internal lead had come slightly loose (a manufacturing defect), overheated as a result and eventually broken the electrical connection. You could only just make out discoloration on the brush block, it all looked basically OK, but a simple digital ohmmeter revealed all. I think my pocket ohmmeter cost $12 twenty-five years ago.
Now I figured I’d need to scrounge up a used brush block, or call Hartzell and beg them for one (the unit is out of warranty but only has 200 hrs) or something along those lines. However a quick internet search showed that I’m not the first one to have this trouble. Hartzell in Alabama (née Kelly Aerospace, the PMA has been passed between several companies since Prestolite went away) has an upgraded and improved assembly available for under $200 delivered, and it could be at my house overnight by UPS Ground. The rest is just reassembly and A&P logbook sign off.
Notwithstanding that $177 plus shipping is a lot for a 1970s-tech brush block assembly how much do you think all this would have cost if I’d just taxied the plane to a maintenance shop or mechanic and instructed them to “fix it”? My guess would be $200 to diagnose a bad alternator, $1200 for an overhauled replacement, $300 to install it for a total of $1700. They would never have bothered to check the brush block because if they found nothing they could not defend the bill for time spent. Easier to order an overhauled alternator and install it, billing for the time spent and not going down any rabbit holes.
However in my world $200 is better than $1700 for exactly the same result.
Good story, thanks for sharing it. I’d also add that for some people like me, it’s fun to fix things. 
If you can find a mechanic that will let you help, indeed it can save money. Many mechanics don’t want this for reasons, and many shops won’t allow it for other reasons.
If you enjoy this kind of activity, it can be very educational to get under the cowl, or under the panel and learn more about your aircraft, and aircraft in general.
Another example: overhaul brake cylinders is some 25€ each (two in total) for the exchange parts. Taking it out, bringing it home for cleaning and replacing etc maybe took three hours.
They are available as replacements four digit price what I have found when I wanted to do it. Getting the air out of the system is hell, though…(but another point good thing to know about)
Die inspection of the stabilator assembly was less than 300, but only after I delivered the very part to the examiner for checking it while I disassembled and reassembled the arrangement myself.
And yes it’s a lot fun to do and get to know all that…
The thing is, would you do it on a Cirrus, a Diamond or other modern aircraft?
Many of us will remember all the electronic gizmos being introduced in cars. No one would touch them if they didn’t have all the expensive testing kit. Nowadays you can buy the plug in thingamys cheaply and connect your car to your laptop to diagnose the problems.
Don’t know about the Diesel engines, but a Cirrus is firewall forward totally antique, like all the others. And I highly doubt that the other examples given above are different, either.
I don’t know much about the Cirrus but eg the DA 40 one of those computer diagnostic thingamyjigs. I don’t fancy messing with one of those. I don’t mind getting my hands oily on lycosaurus, rotax or limbach. Although I need a bit of expert guidance. I am not knowledgable enough to do what Silvaire did on my own.
gallois wrote:
Although I need a bit of expert guidance. I am not knowledgable enough to do what Silvaire did on my own.
With a bit of reading, for example a book like Aeroelectric Connection which is available in PDF for free, and you will have a much better understanding of these systems. You will be shocked to find out that while electricity is truly magic, how it all works is pretty simple.
The problem is I know the theory, it is the practical that is the problem. Perhaps I should have said I am not confident enough to do such a job without guidance.
Thank you Silvaire. It is typically what I like to read in this place.
I wouldn’t like to own an airplane without a setup similar to Silvaire’s.
But, despite years of engineering studies, and being called an engineer, I have very little understanding of how this simple stuff actually works.
I am a paper pusher 
I try to educate myself in maintaining my cars but it’s not the same.
I guess the only to really know is to get a mentor, buy a plane, and work on it (and learn through all the troubles you face).
Great story
And why ownership management is important.
12V aircraft = 1970s car
or perhaps
24V aircraft = 1970s truck
