500SEC Bent rotor arm after 50 miles

[grober]

Nothing lost by trying out a new bosch rotor arm with a BOSCH distributor cap. Looks as if you have the correct coil and transistor unit and wiring for your car then. Can't see how a faulty coil could lead to overvoltage if the primary and secondary coil continuity and impedance check out. Which leaves the transistor switching unit- MERCEDES never divulge the internal circuitry of these boxes but I note its got a lid with screws- might be worth a quick internal visual check? all else fails and the arcing continues a swap to the newer smaller design [ same part no] of transistor switching unit shouldn't break the bank?

 

[Gear1275]

Sounds like a wise way to go to me!
I will do a few miles and see how it looks. I don’t see it being the coil either. I have rechecked the timing too and that’s spot on (TDC at idle with no vac advance) and the vacuum advance is fine (checked with vac pump, holds vacuum and visually moves to advance timing) still got a slight little miss at idle tho but not anywhere near as much and when I put it into gear it drags the revs down and to 550 and makes the miss feel worse as it’s under more load.
Doing the box oil and filter and checking vac line to gearbox module on weds.... then maybe a smoke test to confirm no vac leaks that I can’t find by looking at all the lines in depth...
Thanks again for your help, it’s been super helpful.

 

[Larkone]

Have you thought about replacing the HT lead between coil and distributor - low cost and a possible cause of the issue as well as the misfire

 

[Gear1275]

I checked all of the leads for resistance and they checked out (1kohm) and they are only a few years old. A set of leads won’t do any harm tho, I agree. I will look to get a set priced up Monday...

 

[spike60]

I have a June 1985 500SEC which starts and runs well aside from being a bit lumpy on cold idle. Let me if you want me to check any part numbers etc for comparison though you seem to have plenty of info to work with. Aside from what looks like a dealer fitted immobiliser the car appears standard.

 

[Gear1275]

It can’t do any harm if you want to put some pictures up

 

[Gear1275]

It can’t do any harm if you want to put some pictures up

 

[spike60]

I took some pics but i'm not sure there's much point in posting them. I have the same control unit as you with no sign of any ballast resistors aside from the heater one. Coil, cap and rotor all seem to be Bosch, cap 9 290 004 565 and rotor arm 1234 55 2337. I can't see a coil number and the cap one is difficult to read, if it's important I can post the pics and see what you make of it! The car pre facelift and I was told it was a Lorinser prepared car from new, if this was only cosmetic or affected other things I don't know.

 

[spike60]

Sorry, typo on the rotor arm number, should be 1234 33 2337.

 

[Gear1275]

Mini update...
So far so good!!
Rotor arm has no burning at all and the car is running sweet!
Thanks again for all of your help