Some time ago, Ian Bleeding Knuckles posted an image for on my thread which shows the back of the boss looking very close to the alternator body.

https://www.fiatforum.com/500-classic/447049-faulty-fan-impotent-impeller-3.html?p=4550261

JumpJet said:

There's virtually no gap between the bearing and the housing,

Click to expand...

Matt...duff info that I gave previously; the image was of a spacer for the dynamo version, which reminds me, I must dig out all my 499cc-specific, engine parts and move them on to someone who needs them.

Anyway, in seek of forgiveness, I've hauled out an untouched-from-factory, 652 engine, with Marelli alternator. The spacer is just as the one you have. The clearance at the back of the alternator is minimal, but there is a disc covering the view of the alternator bearing. I can't remove this without dismantling the alternator, so I'm unable to give a thickness. Chances are that they used exactly the setup that you have decided upon, with shim-washers.

Incidentally, they used a good number of shims to keep the impeller from catching on the inside of its cowling...the most I've ever seen. And there's also some nice, bright, fabric washers fitted.

So you're on the right track and doing it exactly as ex-factory.

fiat500 said:

Matt...duff info that I gave previously; the image was of a spacer for the dynamo version, which reminds me, I must dig out all my 499cc-specific, engine parts and move them on to someone who needs them.

Anyway, in seek of forgiveness, I've hauled out an untouched-from-factory, 652 engine, with Marelli alternator. The spacer is just as the one you have. The clearance at the back of the alternator is minimal, but there is a disc covering the view of the alternator bearing. I can't remove this without dismantling the alternator, so I'm unable to give a thickness. Chances are that they used exactly the setup that you have decided upon, with shim-washers.

Incidentally, they used a good number of shims to keep the impeller from catching on the inside of its cowling...the most I've ever seen. And there's also some nice, bright, fabric washers fitted.

So you're on the right track and doing it exactly as ex-factory.

Click to expand...

Peter,
No worries; you are forgiven! Thank you so much for these pictures. The thrust washers should arrive today, so I can get to the task of seating the spacer/fan and hopefully move on to figuring out my alternator-to-fan housing stud corner that I've painted myself into.

I reckon that if I need to build some space to clear the fan itself, I'll just hand cut some gasket material or rubber sheet that I have laying about.

To save money, in both materials and time (i.e. labour), being that the adapter is a tight fit on the alternator shaft, I reckon that Fiat only pushed the adapter on far enough that the flat surface of the adapter was flush with the shoulder of the plain section of the alternator shaft.

the hobbler said:

To save money, in both materials and time (i.e. labour), being that the adapter is a tight fit on the alternator shaft, I reckon that Fiat only pushed the adapter on far enough that the flat surface of the adapter was flush with the shoulder of the plain section of the alternator shaft.

Click to expand...

That would be the easiest to press on uniformly, but without a backstop, any tightening of the nut would draw the adapters toward the bearing face. Based on the pics you've sent me and others have shared, it seems to be just a QC issue with my particular alternator - either lacking a spacer or a housing out of tolerance. It didn't come with nuts for either end, so there's a chance a spacer was lost in the mix as well.

UPS is inbound today with my 17mm ID/30mm OD washers, so fingers crossed this will be solved shortly.

In the 3rd pic kindly provided by fiat500 you can see a spacer/washer covering the bearing....unless I've got it wrong again?

The alternator I was looking at is the same as the one that Peter has shown and like Peter I cannot remove that spacer so I just measured the depth of recess with that spacer in place and it was 0.6mm (0.024”). As you state the depth without the spacer is 0.125” then near as dammit you will need a 0.100” spacer.
Also I have had the occasion to replace sheared or damaged studs that secure a dynamo or alternator to the tinware. I found that M6 coach screws are perfect for the job fitting the square hole and tack welded on the shallow head.

Progress! The spacers arrived and fit perfectly (a break at last!). I went ahead and used all four and wound up with about 2.5mm of standoff between the fan mount and the alternator housing.

With that situated, it was time to mock it up and check the fan fit. As suspected, my previous riv-nuts wouldn't clear the fan, so I cut them out and followed Tom's advice to use the countersunk main bearing bolts as stud stand-ins. I debated using the star washers that accompany them and forgoing the welding, but I know that would come back to bite me some day. Man, those are some close tolerances between the shrouds, but everything is clearing. You can see that sometime in the past, someone else did some ugly welding on the front side of the fan housing. It's ugly, but doesn't interfere.

Next step is to tack weld those two bolts into place and continue on. I just unboxed my new FCAW welder last night, and haven't done any sort of welding in ~25 years, so a little practice is in order before I tackle the real deal. It doesn't have to be pretty, but I don't want to burn through the housing.

Appreciate all the help thus far!

Not pretty, but they should hold... and they’re hidden anyhow.

Behold, I am now rebuilding a Marelli alternator. The spacer washer in question is now removed and measures at 2.5mm thickness. It is simply placed before fitting the impeller and removable whilst the bearing is in place.

Well, would you look at that! Last-pass quality control was lacking at the refurb facility I suppose. Probably why mine was lacking the nuts and woodruff keys too.

Speaking of... got a spare woodruff key? haha

fiat500 said:

Behold, I am now rebuilding a Marelli alternator. The spacer washer in question is now removed and measures at 2.5mm thickness. It is simply placed before fitting the impeller and removable whilst the bearing is in place.

Click to expand...

Peter, since you’re rebuilding a Marelli, I’ve got a quick question... the below circled post is the “D+” to the charging light, correct? The main B+ is labeled and this is the only other post I see. Thanks!

Matt

JumpJet said:

....quick question... the below circled post is the “D+” to the charging light, correct?

Click to expand...

Hi Matt, you'll see in my photo, you're correct about which is the D+ terminal. To see it, I had to clean off some crud and use a magnifying-glass at first. But, for confirmation, use your specs and I think I can jus make it out on your brush-holder too.

Many thanks! The crud actually makes it easier to see the text! I guess mine was too clean to make out; I'll have to go look closer.