Technical Testing distributor

[Paolo66]

How do you test the distributor bob weights are working correctly? I suspect mine aren’t functioning correctly. Can’t find anything in the manuals about this only to put some oil on them.

Also when you use a timing gun where do you connect the positive and negative cables up to as the battery is in the front (obviously)?

Thanks in advance
Damian

 

[gordinir8]

You can connect the positive on the ignition coil red cable and the negative to any ground, I am using the bumper. As for testing the counterweights I think there is a special shop equipment for this job but I don't think you can test them at home.

Thomas

 

[g8rpi]

Not Fiat or 500 specific but normally all you can check on the bob weights is for worn pivots or broken springs.Obviously make sure the plate is free to move too. Some have a force check for the springs but you need a force gauge. Only way to fully test is on a bench rig that spins it up while measuring the advance angle.
If pivots and springs look OK the probably are.


Robert G8RPI

 

[Toshi 975]

How do you test the distributor bob weights are working correctly? I suspect mine aren’t functioning correctly. Can’t find anything in the manuals about this only to put some oil on them.

Also when you use a timing gun where do you connect the positive and negative cables up to as the battery is in the front (obviously)?

Thanks in advance
Damian

If you have not done so yet and you are using a strobe then it is best to highlight the 10 degree BTDC Mark on the timing chain cover and also the TDC mark on the crankshaft pulley. A drop of white or silver paint is best but have also used tipex or a chinagraph white pencil. It is difficult , well actually impossible to get a straight on view of the timing marks unless you have the rear panel removed with the engine supported. I have sometimes stuck a small mirror on a lump of bluetack to the rear panel then play with the angle until you get a clear view of the marks when the strobe flashes. So on tickover the marks should line up at the 10 degree BTDC mark then when you Rev the engine slowly you should see the reflected mark on the crankshaft pulley move in an anti-clockwise direction. In other words advancing the ignition via the Bob weights. Distance will vary depending upon which distributor you have as the advance increased with subsequent 500 & 126 engines.

 

[fiat500]

I think that it's more important to check the advance is correct at high engine speed, or. maximum advance, and then live with static advance possibly being slightly out. If in doing that the static advance is way off target then you know that your advance mechanism is faulty in some way.

 

[portland_bill]

Most reliable 12v feed would be at the starter motor, if accessible. Any good earth will do for the negative.

To properly test the advance mechanism you need the advance details. Sometimes this is a graph or table showing degrees advance for certain engine speed steps, sometimes just a maximum at an engine speed. Whichever, it should not advance too early or too late.
Pay particular attention to whether this is tested with vac connected or disconnected, and if disconnected, is it blanked or left open. Usual method is disconnected and blanked to prevent extra air entering the inlet manifold. Vac advance/retard can be measured too.

You need a timing strobe with a degree gauge or dial.
Highlight the TDC mark.
With engine warm and ticking over, use the advance dial on the strobe to align the TDC mark and note the advance. Adjust as necessary.
Raise engine revs to first step and adjust the strobe dial to get a reading. Compare with the graph or table.
Repeat for other steps.
Repeat again for vac check.

If anything is wrong, causes will be general wear - slop or stiffness, weak or wrong springs, or vac diaphragm perished. Repairs best left to a specialist if you can find one, as they will have parts, an assortment of springs and a test rig.