Hey,

Out cruising (can you do anything else?) on Sat and after maybe 20 mins of driving the engine became noticably more noisy, rumbling.

On closer inspection it was coming from the dynamo. I took the belt off and ran the engine and no noise.

Now when I got the car 2 months back the belt was super lose and was whipping around with the engine running.

3 weeks back I took out 2 spacer washers to tighten it up whist still leaving over 1 cm of play.

It had been running great since.

When looking at the engine on sat the belt now seemed quite tight.

Once home I added 1 washer back in to add some slack. Started the engine and it sounded fine again and took it for a spin and it sounded fine.

But when you kill the ignition it sounds noisy again as the engine comes to a stop.

This morning I started it up and again the noise was there for maybe 3 mins but as the engine heats up the noise disappears. All good until you turn it off and it briefly comes back before it stops.

So, has the dynamo bearing been overstressed as I fear and the heat' s just playing tricks or is there something else I've overlooked?

You thoughts as ever are much appreciated.

Ozza

Ozza, have you tried spnning it by hand with the belt disconnected?
I had an unusual noise which I traced to old, dry bearings in the dynamo.
https://www.fiatforum.com/500-classic/423547-dynamo-bearings-type.html

Or in my case the nut on the back of the Dynamo shaft had come loose where it attaches to the fan. As Peter said about spinning it by hand is how I discovered my problem. At first I thought I had a serious problem as it sounded horrible but was mighty relieved.

Tony

Ok guys will investigate further tonight!

Vitesse said:

Or in my case the nut on the back of the Dynamo shaft had come loose where it attaches to the fan. As Peter said about spinning it by hand is how I discovered my problem. At first I thought I had a serious problem as it sounded horrible but was mighty relieved.

Tony

Click to expand...

So I took a listen tonight.

There is a audible and feelable(?) clunk when you go from clockwise to anticlockwise rotating the pulley with the belt off. But there is no axial play in it at all.

It also sounds like the noise it coming from the front end of the dynamo when the engine is running cold or stopping not the fan belt end.

As said it feels as if something that's connected to the same shaft has a loose connection to it.

So 'if' it is the fan nut how to you get to it to check ????

Cheers

Ozza

ozza said:

So I took a listen tonight.

There is a audible and feelable(?) clunk when you go from clockwise to anticlockwise rotating the pulley with the belt off. But there is no axial play in it at all.

It also sounds like the noise it coming from the front end of the dynamo when the engine is running cold or stopping not the fan belt end.

As said it feels as if something that's connected to the same shaft has a loose connection to it.

So 'if' it is the fan nut how to you get to it to check ????

Cheers

Ozza

Click to expand...

You need to take the big ventilation pipe off the fan housing Ozza. Also it helps to get to it by removing the air filter cover and pipes running to the carb. If you are small and bendy enough you can get in the gap with your arms and you should be able to feel if the nut has come loose, if so I think it's a 19mm, you need a socket on an extension bar to tightened it, with a spanner on the other end.

Tony

Vitesse said:

You need to take the big ventilation pipe off the fan housing Ozza. Also it helps to get to it by removing the air filter cover and pipes running to the carb. If you are small and bendy enough you can get in the gap with your arms and you should be able to feel if the nut has come loose, if so I think it's a 19mm, you need a socket on an extension bar to tightened it, with a spanner on the other end.

Tony

Click to expand...

So it looks like tomorrow night I will be finding out if I'm small and bendy enough!

Bad news. Fan nut is on tight so it's not that. Everything feels good except for slack in the axis of rotation between the fan itself and shaft. I don't know of the fan is on a key but it feels as if there is slack on that key way but nothing else.

The noise is generated by the actual power pulses from the crankshaft pulley through the belt and onto the shaft. So at low revs the slack is being repeatedly taken up and released against the mass inertia of the fan itself. As the revs increase this chatter decreases as the power pulses become more frequent.

All very interesting but no closer to a solution.

The fan is keyed but with very little of it proud of the shaft so I quess it could shear easily.
The dynamo is going to have to come off now.
If you can loosen that fan nut the job is straightforward.
I ended up taking off the whole left side cowling.
I the dynamo is salvageable I would plan on renewing the bearings, brushes and springs at the same time. since removing it is such a PITA
PS. Don't forget that there's the two disc washers and probably a few shim washers in there and they need to go back where they came from.

Peter et all,

If I could get the 17mm fan nut off does the dynamo still need to come out or could I remove the fan and fit a new one with the dynamo in situ or is the fan bigger than the inlet port?

If the dynamo needs to come out does anyone got a step by step guide to getting the dynamo and fan out (assuming I can budge the 17mm nut holding the fan on?), the Haynes manual is vague to say the least.

Cheers

Ozza

Hi Ozza, You can get the dynamo off with the cowling in situ (with a bit off good luck(.
You must take the cowling off to change the impeller or to properly inspect it.
I can tell you what I did a couple of weeks ago when I had the impeller and the dynamo on the bench.

1. Remove the dynamo pulley and all spacers as well as the two dynamo wires.
2. Don't follow Haynes with a 17mm spanner on the pulley nut or try any jamming of the three studs. Use some large Stillsons or possbly an oil filter wrench to grip the pulley flange. A 17mm socket on the nut at the back,of the impeller turned in normal, anti-clockwise direction should remove it. Mine seemed really tight but when I got a good grip on it it wasn't at all. Then move to stage 4 unless......
3. If you're getting nowhere with this remove the nuts that clamp the two halves of the cowling together and to the crankcase and head. there are a number of ancillary bits needing taking off and that will be obvious, I think the back and top piece come off at this stage.
4.You also have to remove the two M6 nuts holding the dynamo to the cowling and the long tensioning bolt on the dynamo strap.
5 With the impeller removed (keeping note of spacers and clamping washers each side of it), the dynamo should wiggle out. because I did it the long way I think I must have removed the front of the cowl and the dynamo as one.

It's not really a hard job, just long-winded and needing method.
Good luck. PS. Haynes is rubbish on many things.

Thanks Peter,

I take it it goes without saying to take the boot lid and cross brace off? Just checking!

Oz

ozza said:

Thanks Peter,

I take it it goes without saying to take the boot lid and cross brace off? Just checking!

Oz

Click to expand...

I removed neither but the engine lid removed would help.

Hello Peter,

Got the fan nut off last night which is a positive but then ran out of time to progress further.

A few questions (sorry!).

I see Axel Gerstl has 2 fans available, I'm assuming the cast Ali one is probably the stronger and better balanced unit though they would both fit?

https://webshop.fiat500126.com/katalog/artikelinfo/694/aluminium_fan_wheel

https://webshop.fiat500126.com/katalog/artikelinfo/771/fan_wheel

Also the fan seems a snug, but free spinning, fit withing the cowling from what I can feel. Once I have got the dynamo off the cowling should it be easy to refit it all in the correct place relative to the cowling to allow the new fan not to rub or is it worth scribing around the dynamo mount to the cowl first.

You help as ever is much appreciated, I hope to order the fan today.

Well done for getting it all apart. I am not the one to advise regarding the gains or otherwise, to be made with the aluminium fan. Personally I think the original one is perfectly adequate.
First, have you made certain that the key-way is damaged? What state is the key in and is the dynamo shaft and the key-slot OK?
When you extract the dynamo take real care, having saved the large, dished washer under the nut, to get a hold of the similar one on the other side of the fan and behind that there will probably be several slimmer washers or shims. If refitting the same fan, so long as you haven't lost any shims and as long as they are put back, there should be no problem. But a new fan may have small dissimilarities and more or fewer shims will be needed to avoid rubbing on the cowl. That can only be worked out by trial and error.

Nope, no idea about what is damaged until I get it out really as it's all by feel at the moment.

I suppose any dropped parts can be retrieved once the fan is out? The key is though to knowing exactly where they came from!

One last question. Did you have to remove the fuel pump the take off the cowling Peter?

ozza said:

I suppose any dropped parts can be retrieved once the fan is out? The key is though to knowing exactly where they came from!

Click to expand...

If you are just removing the dynamo you can leave the tinware alone and just leave the fan in place. If you want to remove the fan as well you can just remove the rear fan housing. As for dropped parts I have found many items down at the bottom of fan housings when stripping down engines. Spark plugs being the most common item but also the odd socket or spanner. I also once changed the fan on an engine and after driving the car away from the spot where I had worked on it I found that the woodruff key had fallen out and was on the ground. So I had to do it all over again

Toshi 975 said:

If you are just removing the dynamo you can leave the tinware alone and just leave the fan in place. If you want to remove the fan as well you can just remove the rear fan housing. I also once changed the fan on an engine and after driving the car away from the spot where I had worked on it I found that the woodruff key had fallen out and was on the ground. So I had to do it all over again

Click to expand...

eek indeed about that woodruff key!
I didn't need to take off the fuel pump even though I removed all three bits of cowling. You could take off the dynamo and separate the fan from it with just the rear piece off. The job just seemed easier with me when I had really good access.

fiat500 said:

eek indeed about that woodruff key!
:

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It was just one of those things when these little cars demand a little bit more love and attention when you think that you have done all you can . Kind of more like relationship than ownership
I forgot to mention that the original fans are normaly fine on a standard engine but if you have a higher reving tuned engine then you need something more robust like the alloy fan as the original fans have a habit of "letting go" at high revs and can get quite messy. Also 126 fans have extended blades over the 500 , good for cooling but more of a drain on power if you are running a standard 499ccs motor.