sticky dizzy

[dhla40]

Has anyone had a problem with the advance weights sticking on a marelli distributor?  When I removed the cap the rotor arm would not turn untill I fiddled with it then it sprang back.  On removing the arm I found it was possible for the weight to catch on the edge of its mounting plate on full advance though wether this could occur with the engine running I am not sure.  On bosch dizzys the weights slide on a plate that extends to the edge of the housing and I am cosidering making a similar mod to stop the weights dropping off the edge of the plate.  Any thoughts?

Sean

[Neil Lewis]

Both Marelli distributors I had had very sloppy balance weights.  Basically the pivot holes in the weights had worn badly and that causes the ignition to get over-advanced and, in extreme cases the weights carve a groove in the dizzy cap.  The only real solution is to get some new (or at least less worn) weights.

I fitted some thin washers between the weights and the springs to stop them flailing about; probably the cause of the excessive hole wear.  And a small blob of grease (and I mean small) on the pivot should reduce the metal to metal wear between pin and hole.

Neil

[dhla40]

Hi Neil

Yes my weights are incredibly sloppy, I was thinking of the washer option too but when I have the dizzy out to fit electronic ignition I will try to mount a thin metal plate under the weights to give them something to slide on.

Sean 

[nistri]

Hi,
The weights are supposed to be sloppy. Note the different length of the two springs. I suggest to apply just a little bit of grease to reduce friction. Too much grease gets splashed inside the dizzy cap and creates misfiring (a common problem of overenthusiastic servicing).
Andrea

[Neil Lewis]

The weights are supposed to be sloppy.

Yes but not so sloppy that they flail about and wear a groove in the dizzy cap.  It's the sloppiness which wears the holes oval and that causes them to be more sloppy; a vicious circle!

Neil

[nistri]

Hi Neil

"they flail about and wear a groove in the dizzy cap"

  Are you sure? How can they get through the rotor arm which is firmly fixed by two screws to the dizzy?

I am not sure that the ignition can be overadvanced by loose weights when the car is running normally on the road. At standard engine speed the influence of the weights on advance is lost, right?

Of course, if the weights are badly worn, I agree this is not good for engine performance. I might also suggest that the distributor could be worn with a large degree of axial play (up and down): this should be within specs (see manual), otherwise ignition firing is erratic. The cure isd to fit shims of the correct thickness.
Regards, Andrea

[Neil Lewis]

Yes you are quite right, but flailing weights can easily break through the thin plastic skirt on the rotor arm (it goes brittle with age) and then they can come into contact with the dizzy cap.

The two spring shave different tensions (springiness)  loop on the thicker (stronger) spring is elongated to allow the weights to move a bit on the weaker spring (at slow engine speeds) and, once that's been taken up, under the tension from the bigger spring.  That way you get two advance curves with maximum advance at about 3000 rpm.  The curves can be tuned by fitting springs of different rates but I wouldn't recommend that unless you've got a rolling road to play on and lots of test equipment!

Sloppy pivot holes will inevitably mean too much advance at full speed which means the static timing will have to be retarded.  That then means the timing is not right at idle.

I've only played with all this so I'm no expert, but my rally car's 1300 engine was reckoned to be pretty good.  Mind you, it had lots of other subtle mods too...

Neil