I need some help here. I just finished installing my new 351w and ran it for 20 minutes last night doing the cam break in suggested by Comp Cams. That went smooth, no problems other than my old radiator hoses were leaking. Today, changed the oil, installed new ignition module, new radiator hoses and refilled the radiator. Went out to take it for a test drive and try to seat the piston rings. Made it 100 feet and realized I had lost transmission fluid and stopped to add fluid. Still didn't feel right (I knew I'd lost some fluid due to a leaky trans. pan gasket) so we headed to the conveinence store to get more trans fluid. Store was no more than 1 mile away, so drove there, got the fluid and decided to head back so I could consult the manual and be sure to check the level properly. On the way back it smelled like something was getting hot. Kinda figured with a new engine, new exhaust, fresh paint on everything a little odor wasn't too bad and we were only going another half mile. When we parked it we shut it off and my buddy popped the hood release and I walked up front and saw flames!!! Got the hood up and saw it was my alternator. Got the flames out, which were mainly coming from the wire connector nearest the bottom on the alternator. After calming down realized I also had a pretty bad coolant leak up on the fitting on top of the lower intake just behind the thermostat housing/outlet. So, any guesses why the heck my alternator caught fire? I can't think of anything that is wired wrong. The only wiring done was unplugging and replugging all the connectors. No new wiring or anything. My only idea is maybe the coolant was spraying on the alternator and caused it to short out somehow. I am sort of at a loss here. We also realized that before running it last night we didn't add coolant to the block, just filled up the radiator. I was worried that maybe without coolant in the block reaching the thermostat it wouldn't open up and take the fluid from the radiator. But, we did run it last night for 20 minutes at 2000 RPM with no problem. It got nice and warm but not more than I would've expected. Right up to the "L" in the Normal on the gauge. But then again, without coolant reaching the temperature sensor is that reading accurate? I put alot of time and effort into this motor, and needless to say right now I am pretty discouraged. Any help is greatly appreciated! Sorry this is so long, BTW. Truck details are in my sig. --Eric

 

Okay, that's pretty weird, but... I doubt the rebuild has anything at all to do with the alternator, unless
you did get a wire wrong, but even if you did wire wrong or pinch a wire somewhere during re-assembly, I still
think it's a coincidence or strange timing. Also, if you pinched a wire it should have shown up during that cam
break-in period. The only other thing there would be if you had a bare wire that didn't touch metal until you were
driving it. There's also the fact that a shorted wire should 1.)burn out, or 2.)blow a fuse, or 3.)burn a fusible
link long before it crisps an alternator. The later model alternators are internally regulated, so it's doubtful
that it was in a over-charging condition, an if it was you should have seen other signs/problems from that. If
there was a major short it should have drained/destroyed the battery, or caused a low-voltage problem that you'd
have seen signs of as well. I know none of these are answers, but just narrowing the possibilities, or pointing
out other clues that might help you figure it out. I doubt that the coolant leak shorted anything. It's a slight
possibility, but not a big one. That alt should theoretically work soaking wet, unless the liquid had a LOT of
conductive material in it. There's also not much in it that can sustain combustion for very long(unless it's
REALLY greasy/oily). Is it? Final thing: Is the alternator "locked up" or really hard to turn? Should spin
freely. I've seen them get MUCH hotter from a siezed bearing than from any electrical failures, although you
did say it appeared to be coming from the rear, so it's possible that it had some diodes short out and cook
off at just that moment, although they are rarely that violent when they go. Don't get discouraged. Look at it
as a separate problem. Inspect the wiring carefully for pinched/bare wires, melted wires/connectors. If it all
looks okay, get new alternator, install and pray. You'll probably be OK.

 

Thanks for the reply! I posted this same message on the big bronco forum and got an enlightening response. It turns out this is a fairly common problem, or at least potential problem, on alternators of this time frame. Ford apparently issued a TSB about it stating that the three wire connector (the one that caught fire on my truck) should be cut off and replaced with a new connector. The connector can deteriorate enough to build up heat and allow the two wires carrying most of the load to contact, thus shorting out the alternator itself and causing a fire hazard. One of the replies I received on the other forum stated that he had replaced his alternator and the new one had a big red sticker on the box stating that the connector MUST be replaced due to a fire hazard. Another sticker was affixed over the actual connection on the alternator. So at least now I know what it was, or at least I'm assuming that was the problem. I guess disconnecting it and reconnecting it was just the final straw and it went. Timing was a little odd, and I'm curious why it didn't do it during cam break-in, but hopefully replacing the connector and a new alternator will fix the problem. Anyway, I sure wish information like this was more widely distributed. I certainly would have replaced the connector much earlier had I known, but what can you do....Again, thanks for the input! --Eric

 

Don't bother you have the flamin 2G and they do burst into flames because of how they transfer the amps through that plug. I would convert too a 3G 130A alternater. Much better alt.

 

I spoke to a guy at the local alternator/starter place here in town. He was very familiar with the problem and said to just bring in my old one and he will build me a heavy duty one to replace it. Seemed to know what he was talking about anyway. Said it'd be right around a $100 for the alternator and plug, and he said if I found one anywhere else cheaper with a lifetime warranty he would match the price. Guess that's the way I'm going.