I would like to say hello to everyone on the forum. I don't own a Fiat per but a 1969 or 70 Siata Spring that uses the Fiat 850 engine. I have the engine running pretty good, new tires, refilled the front shocks and have been changing all of the lighting to LED and HID headlights. It is severely rusted and this winter I will have to strip it and roll it over to fix the undercarriage properly. I am also going to have to get it a new top and a muffler.

My dilemma at the moment is with the generator. When I got the car someone had taken the brushes out of the generator. I purchased it at set and installed them. But it doesn't charge. I can force start it at idle and it will charge but as soon as you rev the engine up it quits never to charge again unless you force start it at idle again. I have a feeling the issue is with the armature though I don't have a growler to test.

I have been looking around a Marrelli alternators for the 850 and it appears that they mount the same in the pictures but Midwest Bayless says that the mounts are different. Before I lay out over $300 for a rebuilt alternator and its external regulator has anyone here upgraded a generator to an alternator on a Fiat 850? Thanks for any and all help anyone can offer.

Take a wander around a wrecking yard and pick up a Nippondenso alternator from any of the small front wheel drivers like a Suzuki swift etc. Might have to change the pulley and fabricate brackets. Usually costs about $40. This is the alternator used by Kit car builders and clubmans.

I have considered fabricating a bracket so I can install a small integrally regulated alternator. What has my stymied is the double pulley. Since the generator is driven by a belt from the crankshaft and then the water pump is driven by the generator. I will certainly consider it though, perhaps I can change to a single belt that catches all three.

^^ As the above picture shows, the Fiat 850 Sport (Coupe and Spider) were fitted with an alternator and separate (mechanical) voltage regulator - getting the parts from one of these models (plus a couple of wiring mods) would probably be the OP's easiest option. There might be some differences in crank, generator and water pump pulleys sizes also as dynamos don't take kindly to being driven too fast, alternator don't mind, water pumps idk about.

AL.

I never did get that alternator. Often this generator would show charging for a short while at idle right after starting the engine. I went for a short drive a couple of days ago and the generator began charging, for a little while then stopped again. It kind of made me think it had something to do with temperature.

I was doing a bit more troubleshooting of the generator and I found that if I connected a test lamp across the armature to field terminals the generator would begin charging, unregulated but charging none the less. I then started playing with the voltage regulator and found that I had been remiss in not checking the contacts of the current regulation coil. The current first has to clear it before going to the voltage coil terminals to feed the generator's field. I found that these were not making good contact.

A little filing and I am charging again. I had to adjust a bit on the field contact mount because when revved the voltage climbed and held about 15 volts. I have that down to about 14v now.

I have fitted my 850 with an alternator. Having modified the water pump pulley to line up with the engine pulley, I made a bracket to fit a Small Suzuki alternator and used a single vee belt to drive both pulleys, the main wire is fitted to the alternator post but where do the three denso wires go? Can anyone help here?
Tony (atomx)

See post #2 above (from "Ramona") for wiring connections.
Or if this doesn't match your alternator terminals, you could try typing 'Denso Alternator Wiring' into your search engine - that'll give you lots of other wiring diagrams to compare with your alternator.