I wonder if “overhauled” is worth the bother.
I am after a spare alternator. It is an ALU-8521LS.
The UK quotes are from 600 to 900 quid plus VAT. NO core acceptance i.e. new units only.
I got one quote for a reputable US firm, QAA in Oklahoma, whose bits I have been using for years, and they are $790, with just $175 for the core. Plus import VAT.
Even if the shipping to the US was free (it is 5kg net) it would not be worth doing because who would want a used part when they have a new one for similar money.
There is a good reason for using “overhauled” solid metal parts (crankshafts, conrods, crankcases, gears, etc) because the used ones, if NDTd, have a proven fatigue-free history, and generally have no fatigue life limits. But is there any point in doing this with e.g. alternators?
There are so many subtle failure modes which will not show up on a bench test e.g. a temperature dependent crack in one of the rectifier diodes, which will create havoc with avionics but will be a total bugger to troubleshoot (in fact I bet nobody will be able to find it, because the only way is with an oscilloscope, probably during flight). The issue I had existed only after a flight i.e. when hot.
Do Hartzell & QAA offer the same warranty? I had a failure on a 1 year old new planepower alternator and Hartzell replaced it promptly (they even paid the shipping to France).
Don’t forget to order that 5$ seal for the prop while you’re at it …
I suppose you’d have to dig into it to get the facts but my impression has been that an overhauled alternator is functionally a new unit, but using an existing serial number to avoid the necessity for PMA. I wouldn’t assume either way because approved overhaul procedures may vary between suppliers.
wleferrand wrote:
I had a failure on a 1 year old new planepower alternator and Hartzell replaced it promptly (they even paid the shipping to France).
Just like you I had an early failure on a brand new Plane-power alternator (an open diode). It had 2 years in service and less than 100H.
Plane-power (now known as Hartzell Engine Technology) sent me a new one but I didn’t even bother install it. The trust was gone.
Plane-power alternators are not overhaulable.
I overhauled the old Prestolite (now also supported by HET) and it has proven to be reliable so far.
Peter wrote:
There are so many subtle failure modes which will not show up on a bench test e.g. a temperature dependent crack in one of the rectifier diodes, which will create havoc with avionics but will be a total bugger to troubleshoot (in fact I bet nobody will be able to find it, because the only way is with an oscilloscope, probably during flight). The issue I had existed only after a flight i.e. when hot
This cannot happen during an overhaul as diodes rectifier are mandatory replacement part (at least on my legacy Prestolite alternator).
So during overhaul, you do get new rectifiers (or if you don’t, it’s not an alternator overhaul as such).
Very interesting input; thank you.
This alternator lasted 2.5 years and something like 400hrs, so is outside any warranty, which in any case would be US based.
I am not sure there is a different P/N which will fit my plane – IO540C4D5D and the specific flywheel the TB20 has fitted.
Very funny about the PMA angle 
I had not thought of that. I know the same process is used for “overhauled” exhausts.
Probably not a good idea to buy a spare alternator because the warranty runs out while it is sitting in the box… Only a reseller can do that.
