General Won't start when hot.

[Vitesse]

I think the confusion is from this quote Tony,
"See if your coil is really hot whilst the engine is running. Also measure the LT side of the coil if it is anything higher than about 12.4v it will damage a standard 500 coil. The resolution is to fit a ballast resistor on the positive LT wire to the coil that will reduce the voltage down"
Rusty500 has an alternator which was the scenario described as being a problem.

Yes I hear what you are saying Peter but that came from a quote from someone else that I posted, personally I wouldn't say 12.9v is excessive from an alternator or even a dynamo, so I would have thought a standard 500 coil should be able to handle that sort of voltage. But then again if the coil insulation is on its way out, maybe 12.9v's is pushing it over the edge.

A coil when the insulation has gone is virtually too hot to touch for a split second, when it's running normally you should be able to put your hand on it for quite a long time.

You can pick up a ballast resistor on eBay in the UK for next to nothing, so it's probably the same in the US????

 

[fiat500]

"that came from a quote from someone else that I posted"

Phew! So you didn't contradict yourself.

Tony, you should be able to settle this question though: although an alternator and even the old dynamo are able to output more than 12 volts, does the battery act as any kind of "sink" to balance that out or can the whole electrical system be carrying significantly more than 12 volts at high engine speeds or when the battery charge is low?

We've been through the whole "9 volt coil for better starting with a resistor bypassed when cranking" scenario before. I thought that was the application for using a ballast resistor. Shouldn't the regulator be ensuring that the voltage remains within safe limits?

 

[Vitesse]

I've heard these coils mentioned before Tony. Do they really make a difference? Is it due to 3 ohms resistance? Electrics aren't my thing
Damian

Damian they just seem to run better on air cooled engines, I don't know if it something to do with the insulation but they produce a crisper, better spark 20,000v's. They also have a built in resistor already so should negate the need for a ballast resistor but the higher output voltage compensates for the ballast resistor. The same model number that you use on a 500 is also used on VW beetles and seems to be the preferred choice of those air cooled guys.

Also 123 recommend Bosch Blue with their ignition as the have carried out testing with it and find it to be the best combination.

I believe Peter has one installed but I am yet to convince him to move to the dark side of 123 and get rid of his antiquated points setup.

I mean anyone who drives around with that sunroof cover is obviously a frustrated modder!!!!!!!

 

[fiat500]

I believe Peter has one installed but I am yet to convince him to move to the dark side of 123 and get rid of his antiquated points setup.

I mean anyone who drives around with that sunroof cover is obviously a frustrated modder!!!!!!!

I do have the recommended Bosch coil and it works well; but so did the original, red Metz coil. It is still in the car but is relegated to being a spare in case of breakdown.

With nearly 44,000 miles driven with the original points distributor and nearly 4 million 500s made, most of which will have travelled at least that distance with the same setup, I feel that the reliability of points has been proven better than the 123. The car starts perfectly every time I want it to, so my modifications will be limited to board game-based, cosmetic additions.....................for now.

 

[Vitesse]

"that came from a quote from someone else that I posted"

Phew! So you didn't contradict yourself.

Tony, you should be able to settle this question though: although an alternator and even the old dynamo are able to output more than 12 volts, does the battery act as any kind of "sink" to balance that out or can the whole electrical system be carrying significantly more than 12 volts at high engine speeds or when the battery charge is low?

We've been through the whole "9 volt coil for better starting with a resistor bypassed when cranking" scenario before. I thought that was the application for using a ballast resistor. Shouldn't the regulator be ensuring that the voltage remains within safe limits?

Well the dynamo or alternator will be regulated by the VR so in the case of the dynamo the VR will limit it to 12.6 volts + or - .2v so as I thought 12.9v isn't excessive in Rusty/Danny's case. I had to get the manual out to check that, I am not that sad enough to remember that's.

That regulated voltage will be available at the battery to charge it but also there is a red wire coming off the + terminal which goes up to the fuse box to supply all your ancillaries like lights, indicators etc... So that red wire will be at the same voltage as the VR output therefore the voltage at the fuse box will the same and likewise at all the + sides of the bulbs, then obviously you get voltage drops across the loads.

So if the battery charge is low and you are driving along, then the same voltage is still being delivered to battery terminal by the VR, therefore all your lights will still work ok. But if your Dynamo output is low, then the wire for the gen light comes off of the same terminal on the VR that the feed for the battery is on and the other side is the battery voltage. So if the Dynamo output falls to 10v's and you still have 12v's at the battery, the the potential difference across the bulb is 2v's and it will start to glow dimly, which is why on the Dynamo cars it flickers when you are stationary as the Dynamo isn't producing enough voltage output.

The battery will only be good for probably 14-15v's as it will start to cook/gas if it is overcharged and potentially blow up if overcharged for long enough!!!

Does that make sense?????? So the answer to your question is yes and yes. Whatever the VR is pumping out will be across the whole electrical system.

I know what your next question will be regarding the alternator output voltage, which is obviously more efficient and produces AC voltage at lower RPM which is converted to DC by a bridge rectifier. A Dynamo produces DC because it uses a commutator. So I would need to read up on how the alternator VR works and what it's cut off voltage is but I would imagine it's all down to the fact that it produces a much more efficient output therefore there is a tendency for it to hold that voltage higher for a long time in comparison to a Dynamo?

 

[Vitesse]

Or that red wire off the battery terminal to the fuse box I think might come direct off of the VR on the F, I can't remember which way round it is? One of the models is different to the others?

 

[Dorisinblue]

Now I am not nearly as clever as you guys - however I have had the same problem with 2 old cars. First is my Jag XK 140 newly fitted with Petronix ignition. It was a nightmare and took me nearly a year to find the problem. Turned out to be the rotor arm shorting on the ignition module. It expands when hot. I called The Distributor Doctor who for a few £ immediately diagnosed the problem and sent me a new, slightly shorter in length rotor arm. They re-manufacture them for this problem.

You may easily tell if this is a problem by switching the ignition off and then on again - it should start.

It is a good item to replace anyway and they make them properly with integrated brass inlay and not the troublesome rivet. They are not low grade pirated copies.

Second was my newly rebuilt 500F, engine and ignition re-built. Started fine when cold but not when hot. Trial and error found me with foot to the floor on the throttle - hey presto off she goes. It won't start any other way when hot.

Might be worth trying these 2 easy fixes.

 

[Berlinette]

Hi,

I've just posted this in response to a similar problem with another forumite, but have you tried checking the distributor cap. Even with electronic ignition fitted, if you have the original distributor cap, they appear to be prone to engine heat and possible cracking. The heat widens the crack, causes a short and loss of power. This could explain why the car will restart after 5-10 minutes when it will have cooled down enough for any crack to close enough to allow the engine to fire up.