Dodgy Distributor Rotor Arm

[melinx]

I've just discovered something on my  'K' reg. 80,000 miles 2.6 Diplomat that I've never seen before in nigh on 50 years of car maintenance

The rotor arm has a black plastic filling in a recess on top of the arm, between the centre connector and the connector on the end of the arm.

I correctly guessed that this filling was encapsulating a suppressor resistor connecting the two brass segments.

The black plastic looked a bit 'crumbly' for about 3 mm next to the centre connector and checking with a meter showed no connection between the two brass segments, no matter how high a resistance range I selected

A spare rotor arm from exactly the same model and year gives a 500 Ohms reading

Digging out the 3 mm of charred plastic and probing the recess with a needle connected to the meter probe gives a 500 Ohms reading to the outer brass segment, so I guess that arcing across a bad connection has charred the encapsulating plastic until it became visible from the outside, producing a gradually increasing gap

Although the engine seemed to be running OK, I can't imagine that a gradually increasing 120 thou' gap introduced into the ignition HT is going to be any help at all

Maybe worth checking ?

[melinx]

I got my new rotor arm today in its GM/Adam Opel packing and it is exactly the same as the spare that I have been using

The original has the Bosch logo and part numbers embossed on it, whereas the other two have no markings at all and the supressor resistor in them is double that of the original ( I don't consider that to be significant at the currents involved )

The outer brass segment on the original is about 40% wider than the other two, so will the replacement cope with the extremes of advance/retard

I note also that the outer segment on the new one is 0.6 mm further out than the original. so I guess that they do wear down with use in the same way that the plug gap widens; this will further reduce the voltage available at the plug

It's possible that GM/Opel are no longer using O/E manufacturers for their spares, so why should we pay their inflated prices when we can get non OEM parts at about 25% of the GM parts ?

[melinx]

The outer brass segment on the original is about 40% wider than the other two, so will the replacement cope with the extremes of advance/retard

Now that the rotor has had enough time to show where the arc is occurring on the brass segment, I can see that at low revs it is barely adequate, with the majority of the arcing right up to the tip of the segment ( I very rarely go above 3000/3500 rpm )

To cut down on the width of the brass segment is not just penny pinching, it's hundredths of a penny pinching.

I'm not amused

[chris]

I bought a distributer cap last year from GM.
Sorry cant remember all of the details but at the time I considered the fit to be less good than the old one and I ssem to recall it wasnt Bosch.
Like you I wasnt impressed especially considering we can get variable quality gear anywhere and go to GM for the reassurance of the correct high quality part.

[melinx]

I bought an Intermotor distributor cap a darn sight cheaper than the Vauxhall part and I'm perfectly happy with it

[Pedro]

I know what you mean about the "filling" stuff!

First time I saw it was when I fitted a new rotor arm last year, and thought "What the __________"

I really think that VX are repackaging Intermotor parts into GM boxes too - and probab;y have bneem fopr a few years! I don't think they expected old Carltons and Senators to still be on the roads of Blighty by now!!!!!