Hi all, I have a 1969 500L. I have found that the distributor on it is from a 500R or 126 with offset keyway on the cap. It had a 500 round rotor arm which it shouldn't have, so I replaced it with the correct type 126 rotor arm. Now the centre electrode in the dizzy cap has almost worn away. I'm totally confused as the 500 type rotor shouldn't work in a 650 cap looking at it, but the correct rotor is wearing out the cap in a short time. Any ideas?

John Pritchett said:

Hi all, I have a 1969 500L. I have found that the distributor on it is from a 500R or 126 with offset keyway on the cap. It had a 500 round rotor arm which it shouldn't have, so I replaced it with the correct type 126 rotor arm. Now the centre electrode in the dizzy cap has almost worn away. I'm totally confused as the 500 type rotor shouldn't work in a 650 cap looking at it, but the correct rotor is wearing out the cap in a short time. Any ideas?

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Hi John, It sound like the parts are mismatched in some way, Are you sure you have a 126 cap and not a 500 to pair it with your rotor arm ?? Maybe there is too much pressure on the centre electrode causing wear?? If in doubt replace everything.
Ian.

I have replaced everything, which is when I found out the cap is off a 500r or 126. The keyway is offset on the 126 and inline with the leads on a 500. Too much pressure on the centre electrode is my thinking too but I don't see why. I am also wondering whether 2 distributors have been used to build one good one, mismatching parts.

From memory the distributor caps are not interchangeable as the locating key you refer to is in a different place. Is it a 499cc engine? Could be that someone has built a hybrid distributor from parts. If you can measure the height from the top of the body to the top of the rotor arm I can check it against a 126 distributor. If you are located near any other forum members then there may be a possibility of comparing distributors.

Toshi 975 said:

From memory the distributor caps are not interchangeable as the locating key you refer to is in a different place. Is it a 499cc engine? Could be that someone has built a hybrid distributor from parts. If you can measure the height from the top of the body to the top of the rotor arm I can check it against a 126 distributor. If you are located near any other forum members then there may be a possibility of comparing distributors.

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Yeah, my thoughts are it's a hybrid. I'll take some measurements when I get chance.

And yes it is a 499cc.

John Pritchett said:

I'm totally confused as the 500 type rotor shouldn't work in a 650 cap looking at it, but the correct rotor is wearing out the cap in a short time. Any ideas?

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I just tested a 500 rotor in a 126 distributor and the engine worked as usual. A 126 cap fits a 500 distributor but the reverse is not true. The 126 cap has a more slender carbon-brush which seems to protrude less than the 500.........doesn't answer your problem but here's the images....126 on the left (except last image):

Thanks for the pics, engine still running ok so will leave it as is. Just ordered some spare caps just in case.

Should my distributor have a spacer between it and the block do you know?

fiat500 said:

I just tested a 500 rotor in a 126 distributor and the engine worked as usual. A 126 cap fits a 500 distributor but the reverse is not true. The 126 cap has a more slender carbon-brush which seems to protrude less than the 500.........doesn't answer your problem but here's the images....126 on the left (except last image):

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John Pritchett said:

Should my distributor have a spacer between it and the block do you know?View attachment 202072

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Yes is the answer. I ran one in my 500 for years without a spacer for years with no problem but it was only when I upgraded to a 123 that I realised the difference.

Have a look at this thread it was discussed in here before. https://www.fiatforum.com/500-classic/461949-need-help-123-ignition.html?p=4362722

Thanks for that, I wonder if the lack of spacer is having an effect on the dizzy shaft and wearing out my cap?

Vitesse said:

Yes is the answer. I ran one in my 500 for years without a spacer for years with no problem but it was only when I upgraded to a 123 that I realised the difference.

Have a look at this thread it was discussed in here before. https://www.fiatforum.com/500-classic/461949-need-help-123-ignition.html?p=4362722

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John Pritchett said:

Thanks for that, I wonder if the lack of spacer is having an effect on the dizzy shaft and wearing out my cap?

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I assume you saw the picture of my dizzy on the other thread and you can see the wear on the gear at the bottom of the shaft only on one half. I would imagine that this one allow a certain degree of ‘slap’ on the shaft as it wouldn’t be fully meshed, so I suppose it could account for the wear?!

Yes saw the pics thanks, took the dizzy out today, no wear on the gear. There is about 3mm movement if you pull the shaft. Is that excessive? My cap is now in a bad state so put the original on and 500 rotor arm.

Vitesse said:

I assume you saw the picture of my dizzy on the other thread and you can see the wear on the gear at the bottom of the shaft only on one half. I would imagine that this one allow a certain degree of ‘slap’ on the shaft as it wouldn’t be fully meshed, so I suppose it could account for the wear?!

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John Pritchett said:

Yes saw the pics thanks, took the dizzy out today, no wear on the gear. There is about 3mm movement if you pull the shaft. Is that excessive? My cap is now in a bad state so put the original on and 500 rotor arm.

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I’ve got my 126 dizzy sitting on a shelf in the garage. I’ll have a look tomorrow and let you know what it’s like.

John Pritchett said:

Yes saw the pics thanks, took the dizzy out today, no wear on the gear. There is about 3mm movement if you pull the shaft. Is that excessive? My cap is now in a bad state so put the original on and 500 rotor arm.

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I checked my distributor if I pull it from the gear end there is zero movement up and down. If I do it from the rotor arm end there is about 1-2mm movement.
It has the round rotor arm fitted and there is no excessive wear on the cap.

Vitesse said:

I checked my distributor if I pull it from the gear end there is zero movement up and down. If I do it from the rotor arm end there is about 1-2mm movement.
It has the round rotor arm fitted and there is no excessive wear on the cap.

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The reason why you have that movement at the rotor arm is because the cam section in the distributor is spring loaded so when the fixing screw is locked down to the spindle the cam will have some movement against the spring.
3mm on the spindle is excessive and probably explains the problem as the helical cut drive will exert a lifting force and lift the whole spindle. It will also alter the ignition timing as it lifts. You need to remove the drive pinion and replace the packing washers that must be missing to give slight clearance and minimal movement.