Diagnose my distributor rotor damage.

[Rollin]

I'm doing the basic servicing and checks on a W123 Mercedes and removing the distributor cap revealed this damage to the rotor.

I don't have massive experience with car mechanics so was wondering what causes this to happen? Is it just wear and tear or a problem elsewhere in the ignition system?

I'm also interested in what improvements I may notice on changing this and the distributor cap? Car seemed to be running OK beforehand.

It may be difficult to see on the photo, but it appears there's no connection between the rotor centre contact and the outer one.

[E-bmw]

What does the distributor cap look like inside?

I have seen similar damage with the centre pin missing from the cap causing sparking from the underside of the king lead connection to the rotor conductor.

[Rollin]

[Turn7]

Rotors and caps used to a disposable item years ago, change them and move on...

[paintman]

Treat them as a service item. Same goes for the plug leads.
Replace both & move on.
Where possible use genuine parts, not cheapie aftermarket rubbish as there's some utter crap around.

Edited by paintman on Friday 17th May 21:04

[GreenV8S]

That composite design is interesting, and I wonder why they did that. Anyway, the conductor has apparently failed so the rotor arm will need to be replaced. If that was me I'd replace the cap at the same time.

[Rollin]

I've replaced the cap and rotor. I was interested if this is the usual failure mode of the rotor, or whether something else will need attention.
I replaced all the leads late last year. The metal attachment under the rubber sheath just pulled away from each cable with a load of corrosion dust present. Car was still running with them on though.

[GreenV8S]

That much corrosion suggests that the boots weren't sealing very well, or the wires themselves were breaking down. The boots should seal reasonably well to the spark plugs and to the distributor. A light smear of dielectric grease can help them seal.

Hard to guess why the rotor arm failed. Maybe it developed a crack, and the resistance caused local overheating that burned the gap bigger. I wouldn't worry about it unless you see similar failures repeating.

[E-bmw]

Probably been in there since new, throw away as above, they are disposable service parts.

[Auntieroll]

The failure the OP shows is/was quite common back in the day. Lucky to catch it in time, before the spark shorted out to the dizzy rotor shaft ! I always carried a spare rotor as a similar failure to the above was one of only 3 enforced stops in over 400k miles in my old 230 TE. ( other were the fuel pump relay and camshaft breaking in two !)
Loads of cars used a similar rotor , the encapsulated component is a resistor which is
Intended to (at a guess) reduce EM interference and /or increase the intensity of the spark.
As other experienced posters have said caps, rotors and leads need changing regularly ,using ,as advised good quality replacements in order to keep both reliability and performance .