My engine mount cracked, and I just replaced it. It had a ground strap on it that bridges the chassis side of the engine mount to the engine side (photo attached).

I haven't seen this grounding strap in any manuals. Anyone have any idea why it might be there? (It's a 126 engine in a 500L body, if that could have something to do with it.)

Thanks.

Do you also have the normal grounding strap from below the dynamo to the chassis, or is the grounding strap in the picture the only one in the engine bay?

It's got an alternator. But still...no ground strap there. Is there usually on a 126?

There should be a hole on the top of the alternator you can bolt a ground strap through, and the other end just goes onto the rear crossmember mount on the left. You can just about pick it out on this image
Chris

Pod500 said:

There should be a hole on the top of the alternator you can bolt a ground strap through, and the other end just goes onto the rear crossmember mount on the left.
Chris

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I do have that threaded hole in the top of the alternator. It would be a lot easier to attach the strap there then one one of the alternator mounting bolts underneath. I think that's what I'll do.

Thanks.

rusty500 said:

I do have that threaded hole in the top of the alternator. It would be a lot easier to attach the strap there then one one of the alternator mounting bolts underneath. I think that's what I'll do.

Thanks.

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I would NOT recommend using the alternator body as the engine earth connection to chassis. This arrangement cases the high starter motor current to flow through the alternator. Any loose connection or mounting bolt could damage the alternator. the earth strap / cable should go to the engine block or starter motor / bell housing. The short strap across the engine mount was probably to reduce radio interference, a short flat strap id much more effective than a longer round cable (inductance, skin effect) at radio frequencies.


Robert G8RPI.

g8rpi said:

I would NOT recommend using the alternator body as the engine earth connection to chassis. This arrangement cases the high starter motor current to flow through the alternator. Any loose connection or mounting bolt could damage the alternator. the earth strap / cable should go to the engine block or starter motor / bell housing. The short strap across the engine mount was probably to reduce radio interference, a short flat strap id much more effective than a longer round cable (inductance, skin effect) at radio frequencies.


Robert G8RPI.

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Really? Mine has always been from the alternator to the rear crossmember and all the ones I've seen have been the same. Are you saying it should go from the rear crossmember to one of the bolts that hold the engine and gearbox together.

Damian

fiat500 said:

Damian, I think Robert is giving good generic advice there in order to expain a principle.
I have replicated as closely as possible the arrangement on the 500 with dynamo. In that case the earthing strap is connected from rear panel bolt to the long bolt for the dynamo which secures it in the mounting saddle/strap. So the nearest I could see was to put the terminal of the cable under the head of one of the four hexscrews which hold the alternator to the block.
Robert maybe isn't aware of the unusual construction of the alternator which is cast in one piece with the mounting plinth, hence your mounting method seems to overcome any possible connection problems.

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Hi,
You are correct, I don't know the classic 500 alternator very well. Even if it is a single cast construction I still think it is best to put any earth lead under a bolt that goes directly into the engine block or gearbox rather than into a spare tapped hole in the alternator casting. A mounting bolt is OK to use. I normally use at least two heavy grounds on the block if doing a modification, but my background is aviation and radio both of which are a bit paranoid about grounding .


Robert G8RPI.

The M6 tapped hole on the top of the alternator is there to mount the suppressor by means of a "P" clip and connects to the large terminal on the alternator. The correct mounting for the earth wire/strap is from the Dynamo or alternator mount back to one of the rear panel mounting studs both on the 500 & 126

I agree regarding that need to earth on the bracket, particularly since you say it's only an M6 tapping.?

This is an original Fiat 500 engine earth lead. Slightly heavy duty wire with 8mms connectors each end. Also in the picture are three M8 stud connectors which are 2.4cms long. I use these to hold in the rear panel. With a dob of grease on the four studs these then cover the whole thread so no danger of rusting up plus they are easy to get a spanner or socket on. I have had those studs shear of before which is a real pain.

So, I get the argument for grounding to the engine block itself, and if I'm going to change the grounding strap, I would ground it from the alternator mount.

However, I'm still left wondering if I need to change it at all. Does anyone see anything problematic about grounding across the engine mount?

No,
no problem at all using the strap across the engine mount.

Robert G8RPI.

This is mine. The alternator is from a 650cc engine and the earth strap has always gone from the casing to one of the bolts that fixes the rear transom.

My other old cars have the strap going from either the rear of the gearbox or engine to the chassis.

Chris

You haven't got the suppressor on your alternator Chris. Do you need it? I don't even know what it does. Just left mine on as that's how the engine was delivered.

I think the suppressor was a capacitor that leaked any stray AC signal to earth so you could listen to your AM radio without too much interference.

As I never had a radio in this car and likely never will, probably don't need it

You do however need to electrically connect the engine to the chassis somehow. Because the engine/transmission mounts are rubber insulated for vibration damping and the starter motor is mounted to the engine housing, the 12V starting current cannot efficiently return to the chassis to complete the circuit with the battery. Without a nice low resistance strap capable of carrying a big current connecting the engine to the chassis, the car will be very difficult to start.

Chris

This is the earth strap on one of my old Alfas. It connects the rear gearbox housing to the chassis and is thick braided copper.

Chris