Distributor rotor button freeplay?

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72Dart360

72Dart360

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I have a MSD distributor in my 360 with missing at idle. The tach just jumps around from 1000 rpms to 1200. For a long time I just payed it no attention because at the strip or when cruising at 55 which is about 3,000 rpm theres no problem with engine miss. The other day I was making a adjustment to the advance springs and noticed that the rotor button could be moved about 10 degress or so.(without moving the advance arms). It seems there is slop, as if the distributor/oil gear drive was worn. I havent taken the distributor out and looked to see if the slot is worn yet. Just wanted to see if someone has heard of such a thing. Maybe its just in my head and something else is the matter. thanks for any advice
 
Take a look at the burn pattern where the spark jumps from the rotor tip to the cap terminals..Are they centered, or way of to one edge? I found a brand new (part of a dyno'd Indy crate motor) that the cap or rotor was not indexed properly. I modified the cap to get the burn centered in the terminals. It helped a poor idle condition. You may want to verify the advance limiting bushing is still in place, also look at the bushing and oil pump drive in the block. I pull the drive out, and if there is any wear/taper/scratches, replace it and the bushing. It can be a little tricky with the engine together in a car, but you need to make sure not to drop any oilight bushing bits into the oiling system, and that the new bushing isnt too tight on the drive after installing.
 
I agree with Moper that you need to take a look at the distributor/oil pump drive shaft. If it's OEM the gear is not pinned and tip is not hardened. This could be causing your problem. You can get a good one from Mancini Racing for around $30.
 
thanks for the advice, i'm getting ready to go out and pull the distributor and gear. I'll let you know what i find.
 
Pulled the cap off and the firing is dead on. Pulled out the distributor and there is a little wear in the gear where the shaft sits in. I talked to a friend with a 340 and he has the same slop but no problems. I'll just live with the idle the way it is. As long as I keep running in the 12's at the strip, I quess it'll be okay.
 
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