burning alternator,landrover disco 300tdi

Got my 97 jap auto D1 (with EDC) running,finally,thanks to all who posted help. Have been running the engine,vehicle parked,for 30-60 mins a time all day to check for leaks etc.Just when I thought all was good... ....smoke pours out of alternator.So I turned it off. Earlier on I measured 14.4v charge,all good.But just now I switched on the aircon and in a couple of mins I noticed a little fluid/acid on the battery ( I had filled it a little generously so thought nothing of it)........then the revs increased a little for a minute,then down again,....then smoke from the alternator. I didnt have time to check what it was putting out at that point as I was more concerned with,well,putting it out.

I am no closer to getting any answers on whats going on. It was NOT the alternator that came with the vehicle (which was labelled GM), that was a Magnetti Marelli of the denso design, of the lucas A127 type......if that makes any sense ! The alternator that had been fitted had been liberally flooded with water and antifreeze on two headgasket failures. So, I fitted the 100amp alt. of the same design that I had on the shelf which was very nearly new but for sitting unused for 18 months.Prior to fitting I had flooded it with switch cleaner and air-line blown it clean and left it to dry completely.For a long time.It has been sitting on thatr car for about 3 months,unused, awaiting head repair. The alt. was fine, running for long periods until I put the aircon and fan on, at tickover. Then revs went up,down,up then smoke from back of alternator.Ignition then turned off,battery disconnected. Granted,this was an old battery but it was fully charged and was holding 12.6 volts and was man enough to start the car. Could a battery fault cause the alt to burn out under load ? Why would and alt. burn out under load ? And what is it that will have burned ? I dont have the unti here with me to inspect or describe. I have the one that was watered....is it worth stripping it and cleaning and then using ? Should I source a repair pack for it ? What is it that will need to be replaced ? Do I need to replace the battery at the same time,given that it still gives good numbers on the meter ? I HAD wanted to get this one into MOT test today,but THATS not happening now ! Any advice,opinions,experience gladly received, however basic....you dont got to be an expert....just tell me what you did in similar circumstances.

You "don't got"? What part of a Bronx accent is that? Oh wait you like gangster movies. The only clue I have here is the contact cleaner. By the way, just like DeWalt, Bosch, Makita etc. Those alternators you mentioned are all built in the same factory! From your post I'm afraid to sound patronising because you do appear to have the knowledge but...the right drive belt and pulley? Tight enough?

Sorry I meant switch cleaner, could there have been an internal short? Was this unit tested previously?

Howie, I wasnt aware that you were the grammar control officer for this forum or I would have contacted you before posting.Yes,I am aware that all those alternators are the same build but others may not be.    Contrary to your patronising post it is not a case of the "drive belt" not being tight enough...that wouldnt cause an alternator to catch fire.The unit was tested and there was no internal short. But thank you for taking the time to reply.

Oh,and I lived in NYC for many years and am married into a family from the bronx.

Note I apologised for any patronising but I had to ask the obvious. I had family in the Bronx but I made sure I spoke Estuary..didn't I.

Howie,saying you are afraid to sound patronising and then doing so is like saying "no offence"....and then giving it. The problem lies with the fact that unless you had announced the said non-intent then no one would have noticed it ! It wasnt the technical part I took offence to it was the grammar/accent part.But whatever,you dont mean any offence so I will take none and apologise for my terse reply. Thank you for taking the time to answer. No,there was no internal short,the unit was cleaned,tested and fitted and all good. Any damp or cleaner would have made itself known much earlier.It was only when the electrical load was increased that the problem occurred - the engine had been running at idle for about 6 hours in hour long sessions as the new-built cylinder head settled in and the previously problematic engine was checked for leaks etc. The unit,used as a high output generator by many car builders has a standard output of 100a sometimes increased to 120a by additional internals.What I was after was some anecdotal knowledge of similar situations as I am aware of theory,have experience and access to all the workshop data. The battery did not visibly boil or heat up and only shed a little fluid from an overfilled cell which is to be expected when charged at 14.4v for hours. I dont want to go fitting another alternator ( I have spares) only to have the same problem. The obvious way round this is to fit a brand new alternator,£100 trade, and a brand new battery,£80......I would rather avoid this if I can. I currently have another marelli 127 63340004 unit in pieces for inspection and may go as far as to get a service pack to replace slip ring ,brushes,rectifier and bearings....even though the unit seems fine,if dirty.It is certainly a cheaper option at around £20 but means more delay.    The serpentine belt on a 300tdi engine is spring tensioned at all times so that is not an issue. The heart of the matter is the time that the alt. chose to burn......when more electrical load was incurred.

Point taken, I was having a laugh at your choice of words, certainly not grammar or syntax, yes I'm terribly patronising especially of those who start their posts with "Hi All" or "So I". In fact leaning more to a joke. The patronising part was about belts etc. I had to ask, first question on diagnostics. The problem is I'm not as au fait on charging systems as I am with relays, diodes, motors etc. I'm hoping Oldspark can comment here. PM him or if no reply by Monday, I'll email him.

Thanks Howie.....I tend to be a little snappy when under pressure,so i...apologise. Im pretty au fait with vehicle mechanics and become annoyed when things happen that have no logical reason that I can see,especially on my own vehicles ! Oldspark is the one who usually bails me out,with footnotes and references to back it up.....I will do as you say if he doesnt weigh in.