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MG MGB Technical - Really Weird Rotor Destruction

It wouldn't start yesteday. Just cranked and cranked. After the normal (knee-jerk) check of the carbs..I popped the distributor cap. Cap was in new condition as it should be as it and the rotor have only 1500 miles - but, the rotor was destroyed. The metal lead from the center top of the rotor appeared melted and the bakelite plastic close to it appeared slightly melted. The metal detached without much effort.

The dizzy is a 45D Aldon, using points, a 6AL MSD box and MSD coil and MSD helicoil wires. Champion plugs....

Do you think the old rotor had a hairline crack that caused arcing?


installed new rotor, fired right up.....

rn
RN Lipow

RN,
I don't know if there is any connection, but a friend in our club mentioned yesterday that there has been a rash of rotor failures due to a bad manufacturing lot.
David
David

Where you using the MSD setup previously with other rotors? Maybe the output was too much for the stock Lucas component, or as suggested, this one wasn't made of "tougher stuff".
Andrew Blackley

What a coincedence!

I have a friend with a MSD-equipped Honda Civic
that went through a similar experience 2 days ago.

The MSD was working fine for many months, then
suddenly it had blown the coil (- it looked like
somebody had burned a 1/4" hole through the top
insulator with an industrial laser); and fried the
coil wire connector, cap and rotor.

My guess is that these things are very intolerant of
dirt or carbon soot, etc., and have to be kept very
clean in order to avoid shorts.

For MGB - there was indeed a bad lot of Lucas
rotors made a while back. Maybe you got an NOS
rotor (New, Old Stock). Typically, they develope an
internal electrical short through the bakelite - and
the spark current is grounded onto the distributor shaft.

Having both MSD, and the bad rotor, probably
made things worse for you.

Before you haul everything out, maybe you could
try another cap and rotor from, say, Bosch or
Borg-Warner.
Daniel Wong

thanks for your responses...this rotor was recently purchased with the 45D from aldon...i have used the same set up with a 43D dizzy (MSD, wires, cap and MSD coil) before...just switched the rotor...perhaps that takes care of it.



"For MGB - there was indeed a bad lot of Lucas
rotors made a while back. Maybe you got an NOS
rotor (New, Old Stock). Typically, they develope an
internal electrical short through the bakelite - and
the spark current is grounded onto the distributor shaft."

dan, I think that's what happened...

thanks again for your prompt and erudite responses.

rn
RN Lipow

Hi all.

A couple of years ago I suffered a sudden total engine failure in my Morris 1000.

There was an internal short in the rotor arm which was totally undetectable to the naked eye.

I kept it, and used to fit it as a security device if I was leaving the car for a few days.

Don
Don

I had a similar experience with a Range Rover a few years ago. The engine had started intermittently missing and coughing and spluttering, so I changed plugs, then points, then plug leads and finally dizzy cap to no avail. Then the engine stopped completely halfway up a short but steep hill! Called the rescue people and they changed the rotor arm, turned the key and that V8 sounded beautiful!!! I had spent about fifteen pounds on parts and the cause was a three pound rotor arm. Felt silly and learned a lesson!
G Webb

RN,
The melted rotor condition is likely created by a gap that has formed between the cap and rotor contacts, often when the carbide bead falls out of the underside center of the cap, or the brass spring (contact) of the rotor is incorrectly touching (or missing) the contact on the cap. The resultant gap causes an arc which is extremely hot. The rotor could also be pushed onto the dizzy spindle too far.

Tyler
tyler

You can also step in the deep doo-doo by leaving the ignition key on while a battery charger is connected.
Dan

RN

There has been a problem over here with rotor failures also. Coincidence or probable cause??
Regards
Roger
Roger

This thread was discussed between 06/10/2003 and 07/10/2003

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