Technical Starter motor issues - Fiat 500F 1970

[ThomasK]

Hi,

I'm having an issue with the starter on my 1970 Fiat 500F.

The car has a pull-type starter, and it no longer starts as it normally would. When I pull the starter using a fully charged battery, it sometimes cranks very slightly, but that’s all. It cannot start the engine.
However, when I use my jump starter (which delivers up to 800A), the starter cranks and engine starts perfectly.

This issue began after a previous ignition failure. During the troubleshooting process of that previous issue, I had to attempt several starts, which seems to have weakened the starter’s performance when using the car’s own battery. That said, it still sounds (and cranks) completely normal when using the jump starter.

Here’s a video showing the starter in action with a brand-new 12V 45Ah 400A car battery:


The starter gets slightly warm during the attempt, as seen in the video.

I’ve inspected the starter brushes and the starter switch (see below for details). I’m considering replacing both, but I’m unsure whether that would actually solve the problem.

Before I order any spare parts, I’d really appreciate your thoughts:
What do you think could be causing the issue?

I have attached some photos of the starters condition.

 

[ZaphodB]

Where are you attaching your jump starter ?

Running the motor unloaded isn't a good check of it's performance btw

 

[bugsymike]

After repeated excessive cranking due to a starting issue, it is possible for the coil windings inside the starter motor to overheat, this melts the insulation causing the starter to be less efficient and ultimately fail, much like an old electric drill and in the same way if you smell the motor it will have a distinct aroma of "burnt windings".
When at an auction or sale where looking to buy anything with an electric motor it was always wise to have a sniff as a guide.
So if yours has that smell then a good idea to have it replaced or get a thorough overhaul including the windings.
If you put a suitable high capacity amp meter on it you would see that it takes a lot more amps to operate it when compared with a good/new starter.
Assuming there was no smell then another area to check is that contact pull switch.
I had a Peugeot 504 diesel with 175k miles on it and the pre engaged starter motor was failing, I was able to take off the solenoid switch, clean the copper contacts and turn the connecting bar over to an unworn area and the starter worked perfectly again. Modern starters etc. are not designed to be rebuilt, just thrown away and replaced.

 

[ThomasK]

Where are you attaching your jump starter ?

Running the motor unloaded isn't a good check of it's performance btw

I am attaching the jump starter to the battery - just as normal procedure.

I know. However, I hoped that the sound itself would give a hint of its condition.

Any ideas what to do/try?

 

[ThomasK]

After repeated excessive cranking due to a starting issue, it is possible for the coil windings inside the starter motor to overheat, this melts the insulation causing the starter to be less efficient and ultimately fail, much like an old electric drill and in the same way if you smell the motor it will have a distinct aroma of "burnt windings".
When at an auction or sale where looking to buy anything with an electric motor it was always wise to have a sniff as a guide.
So if yours has that smell then a good idea to have it replaced or get a thorough overhaul including the windings.
If you put a suitable high capacity amp meter on it you would see that it takes a lot more amps to operate it when compared with a good/new starter.
Assuming there was no smell then another area to check is that contact pull switch.
I had a Peugeot 504 diesel with 175k miles on it and the pre engaged starter motor was failing, I was able to take off the solenoid switch, clean the copper contacts and turn the connecting bar over to an unworn area and the starter worked perfectly again. Modern starters etc. are not designed to be rebuilt, just thrown away and replaced.

Thanks Mike, that is also my fear.
Then I must replace it when I get tired of boosting the car with the jumpstarter

I'll check the smell.

What do you think about the pictures? Does the brushes and contact switch look in OK condition (despite the dirt)?
Any other ideas what to try?

 

[bugsymike]

Thanks Mike, that is also my fear.
Then I must replace it when I get tired of boosting the car with the jumpstarter

I'll check the smell.

What do you think about the pictures? Does the brushes and contact switch look in OK condition (despite the dirt)?
Any other ideas what to try?

The brushes don't look bad as long as there is enough spring pressure to hold them in good contact with the commutator, which of course must be clean and shiny with all the grooves clear.
Generally if the starter gets quite warm after only a short bit of cranking then it does point towards the coil windings, which the smell would confirm.

 

[ZaphodB]

Hi,

When I pull the starter using a fully charged battery, it sometimes cranks very slightly, but that’s all. It cannot start the engine.
However, when I use my jump starter (which delivers up to 800A), the starter cranks and engine starts perfectly.

If everything else you're doing to start the car is the same (battery alone or booster pack), then the only thing that makes sense there is poor condition battery posts and/or clamps. (or the battery itself)

 

[ThomasK]

If everything else you're doing to start the car is the same (battery alone or booster pack), then the only thing that makes sense there is poor condition battery posts and/or clamps. (or the battery itself)

It is the exact same that I do. However, I have already change the car battery without any effect.
I use the jumpstarter directly on the clamps, and I have tried to unmount the clamps and put them back on withou any effect, unfortunately.

What do you think about the pictures? Does the brushes and contact switch look in OK condition (despite the dirt)?
Any other ideas what to try?

 

[ThomasK]

The brushes don't look bad as long as there is enough spring pressure to hold them in good contact with the commutator, which of course must be clean and shiny with all the grooves clear.
Generally if the starter gets quite warm after only a short bit of cranking then it does point towards the coil windings, which the smell would confirm.

Spring pressure is checked - there is good pressure on the brushes. Commutator was quite clean (it was blank and looked quite clean, but I havent dismantled it fully, so I have only checked by taking the brushes out and make a visual inspection from there).

 

[GettinBetter]

However, when I use my jump starter (which delivers up to 800A), the starter cranks and engine starts perfectly.

So there's nothing wrong with your starter motor, only the connections to/from it. (As @ZaphodB said) or your battery.

Don't bother to check resistance, it won't show anything worthwhile. Check every connection for supply and return path through earth.
For the earth, use a temp jumper cable direct to battery, just to prove path is not the problem.
A visual inspection of any terminal connection without dismantling is not acceptable, remove nuts and washers and thoroughly clean all mating surfaces, only after they are all replaced and tight, add protective grease.

 

[ZaphodB]

So there's nothing wrong with your starter motor, only the connections to/from it.

I thought I was going mad from what the OP said it can only be this

However, when I use my jump starter (which delivers up to 800A), the starter cranks and engine starts perfectly.

A good battery can also deliver this sort of short term cranking current, but a poor connection can also rob the starter of the ability to be able to draw this current. As can an aged battery.
Engine cranking is a prime example of a good vtest of a battery condition.

A visual inspection of any terminal connection without dismantling is not acceptable

Absolutely this

 

[GettinBetter]

but a poor connection can also rob the starter of the ability to be able to draw this current

There FIFY, well somewhat.

Anyway ... Yep, been there, done that, got the tee shirt, the hard way.

 

[ThomasK]

So there's nothing wrong with your starter motor, only the connections to/from it. (As @ZaphodB said) or your battery.

Don't bother to check resistance, it won't show anything worthwhile. Check every connection for supply and return path through earth.
For the earth, use a temp jumper cable direct to battery, just to prove path is not the problem.
A visual inspection of any terminal connection without dismantling is not acceptable, remove nuts and washers and thoroughly clean all mating surfaces, only after they are all replaced and tight, add protective grease.

Thanks. I have replaced the battery, which didn't helped.
Also, I tried to connect the battery directly to the starter when it was mounted on the car, which didn't have any effect, unfortunately (same with earth connection).

I'll try to test the earth jumper cable solution directly to the battery - however, the earth connection on motor and battery seems in good condition, hmm..

 

[bugsymike]

All good points, but from past experience I would still test starter for smell and getting hot etc. Re damage to the coil windings of the starter motor.
After all you did mention at the beginning :-This issue began after a previous ignition failure. During the troubleshooting process of that previous issue, I had to attempt several starts, which seems to have weakened the starter’s performance when using the car’s own battery.
I have seen people flog a battery and starter over and over which burns them out. It is always advisable to spin the starter for only a short while, then rest it before having another go.
Generally speaking if an engine doesn't burst into life pretty quick, there is something wrong and killing the battery and starter will only cost you more money.

 

[ZaphodB]

All good points, but from past experience I would still test starter for smell and getting hot etc. Re damage to the coil windings of the starter motor.
After all you did mention at the beginning :-This issue began after a previous ignition failure. During the troubleshooting process of that previous issue, I had to attempt several starts, which seems to have weakened the starter’s performance when using the car’s own battery.
I have seen people flog a battery and starter over and over which burns them out. It is always advisable to spin the starter for only a short while, then rest it before having another go.
Generally speaking if an engine doesn't burst into life pretty quick, there is something wrong and killing the battery and starter will only cost you more money.

This story has a absolutely crucial puzzlement:

The OP states it struggles on the car battery alone, but it starts fine with a booster pack clipped onto the battery terminals

When I pull the starter using a fully charged battery, it sometimes cranks very slightly, but that’s all. It cannot start the engine.
However, when I use my jump starter (which delivers up to 800A), the starter cranks and engine starts perfectly.

If that booster is clipped on to the battery terminals then the battery is fubared - simple , might show 12v with virtually no load (and therefore appear healthy), but when asked to pull several hundred amps to crank, the terminal voltage is dropping like a stone. due to built up internal resistance.

 

[fiat500]

As has been said before, it sounds like the contact surfaces of the post-clamps need cleaning.
The proof is that the jump-pack to the outside of the clamps makes it work; this bypasses the battery connection.
The lead or brass clamps need bringing to a shine using fine sandpaper or a wire brush, they should ideally have a wipe of some electrical grease or petroleum jelly, and then clamped up, with acharged battery, it should work O.

 

[bugsymike]

This story has a absolutely crucial puzzlement:

The OP states it struggles on the car battery alone, but it starts fine with a booster pack clipped onto the battery terminals



If that booster is clipped on to the battery terminals then the battery is fubared - simple , might show 12v with virtually no load (and therefore appear healthy), but when asked to pull several hundred amps to crank, the terminal voltage is dropping like a stone. due to built up internal resistance.

True, since I got my digital battery tester it has been surprising how many batteries don't match the claimed EN etc cranking capacity, often only 65% etc.
The little post cleaner is useful too.
In the old days all we had was a high load test across the posts with lots of sparks, but with tops of battery you could see a duff cell bubbling, not possible these days with sealed batteries etc. Though a lot safer.

 

[ZaphodB]

They just put predermined (fairly insubstantial) loads across the battery and read off the voltage on each load and extrapolate the data to give an approximation of overall battery health based on internal resistance gained from those load tests..

As the load (and current) goes up the terminal voltage will obviously drop because of the internal resistance. (simple I x R)
Cranking on a good charged battery you can easily expect terminal voltage to drop to 9.6 to 10v, anything less than that with a charged battery and the battery is toast.

To test true cranking current capability you'd have to expose it to a true cranking level of load, but the lesser load tests on your tester will approximate it for you.

 

[GettinBetter]

To test true cranking current capability you'd have to expose it to a true cranking level of load

This IS the gold standard test. The others are just cheapskate tests.

 

[bugsymike]

This IS the gold standard test. The others are just cheapskate tests.

These are my other methods, both will read up to 400 Amps for most starter cranking.
From memory I believe @Pugglt Auld Jock has the bottom one, being old school like me.