Originally Posted by Slickriffs
Trying to run down a rough running engine. Changed plug wires..No help.
Pulled the cap and noticed 2 things.
1) Black gease on rotor center
2) one or two brass terminals have a rough burned look
I'm assuming the black looking grease is a lube for the rotor contact? I should know since I'd be the one who put it there..but that was 15 years ago..grease looked filthy...
Is it normal to have only some terminals burned looking? If not what causes it? Too much play in distributor?
You didn't say what year, make, model you're working on ... but 15 YEARS??!!!
Give that poor thing a complete tune-up would ya!
Cap, rotor, wires, plugs, fuel filter, air filter...
I'm going to assume that this mid-70's or newer with HEI / Duraspark ... 8mm plug wires?
Think of electricity like water. It always follows the path of least resistance.
If the plug gap has widened, or the distributor cap / rotor contacts are corroded or the wires have too much resistance, the spark will look for an alternate route. Take the rotor right off and hold it up to sunlight. My guess is that you'll find a hole burned right through the rotor to the distributor shaft!
If you have suspicions about the distributor shaft / bushing being worn out it's quite easy to check. Grab a hold of the distributor shaft and try to move it lateraly. If you can see/feel/hear it move ... it's time for a new dist. (Very few shops overhaul distributors any more. They're becoming an R & R item.)
There is usually no grease used at the rotor contact, just a carbon brush. The blackening is probably caused by the spark arcing and breaking down of the brush or even the rotor itself.