rotor only turns half way around

[bugt]

Yesterday i was going down road about 60mph when all of a sudden i got a couple of backefires and then coasted to the side of the road. after checking fuel,and spark which at the moment seemed to be fine .i tryed to start her up again. she wouldnt start. I pulled the cap off ,jumped the starter so i could watch the points and to my suprise the rotor would turn half way around then stop then when the motor kelpt going around the rotor would start again then go again half way around . is there something simple here or am im going to hear split the case. never seen this . has any body had this happen before and why.

[helowrench]

I would start by pulling the distributor, the you can watch the dizzy drive to see if the problem persists in the drive.
also, attempt to turn the drive itself, since it should not be able to.
thirdly, with the dizzy out, inspect it, and ensure it rotates freely.

Edit: I forgot to addreess an imortant issue. Check Marc's post below.

[Clonebug]

Try reseating the distributor.

Sounds like it is moving up and losing the engagement with the drive.

Loosen the clamp on the distributor and push it down farther into the hole to get a better grip.

Then reset your timing and try again.

[Marc]

Yep, sounds like a classic case of a distributor that climbed out of its hole a little, causing the drive tangs to disengage from the slot in the pinion gear. If you're lucky it was just a loose nut and all you need to do is push it back home (rotating the rotor as you do to feel the spot where the tangs line up) and set the timing like Clonebug said. Fortunately, because the slot is offset slightly it will only go in the right way.
Sometimes the clamp and/or the bolt are bent, making it impossible to get the distributor all the way in. You'll either need to replace it or straighten it out (a bench vise and two pliers work nicely).
IMPORTANT! Any time the distributor is out, DO NOT rotate the crankshaft unless you are pressing down on the pinion. If it climbs up and out of mesh with the brass gear on the crank, the gear will be damaged and that DOES require splitting the case to fix.

[helowrench]

IMPORTANT! Any time the distributor is out, DO NOT rotate the crankshaft unless you are pressing down on the pinion. If it climbs up and out of mesh with the brass gear on the crank, the gear will be damaged and that DOES require splitting the case to fix.

Marc
Thank you for reminding us all especially me about this.
I had forgotten this caveat.
You can turn it one way but not the other without risking this but i cannot remeber which way is safe.

[ONEBADBUG]

If there are no spacers under the drive, it will machine itself down until the distributor doesn't turn anymore.

[bugt]

thanks guys for the replys. have not had a chance to check dis. yet almost scared to now. when i was buy the road i pushed the dis. back down into the slot . but again the motor turned all the way around but the rotor only turned a little around as i kelpt turning the motor at a certain point the rotor would turn a little more. i think maybe the dis came up while going down the road enough to let the shaft moveup enough to damage the brass gear. does this sound like something that could happen.if the dis is in the slot then the rotor should turn around with the motor right . will try the suggestions given ,but i think im going to find i got a messed up brass gear. will post when i find the cause. thanks

[bugt]

HEY GUYS Dont be stupid like me and make sure your dist. clamp is tightend like it should be or you will have to split the case on a 2000mile motor because the shaft moved around and chewed the teeth off the brass gear that turns the dist. you can bet your a== it want happen again sorry for the vent

[Steve Arndt]

HEY GUYS Dont be stupid like me and make sure your dist. clamp is tightend like it should be or you will have to split the case on a 2000mile motor because the shaft moved around and chewed the teeth off the brass gear that turns the dist. you can bet your a== it want happen again sorry for the vent

Doh! Sorry that happened, but you will remember this lesson forever.

[Clonebug]

Go distributorless and never worry about it again......

[Marc]

thanks guys for the replys. have not had a chance to check dis. yet almost scared to now. when i was buy the road i pushed the dis. back down into the slot . but again the motor turned all the way around but the rotor only turned a little around as i kept turning the motor at a certain point the rotor would turn a little more...

It's unlikely that it came out far enough to damage the gear, since it only takes about an eight of an inch for the tangs to come out of engagement and kill the engine. There's a small spring in the end of the pinion gear which is always exerting pressure to push it down; if the clamp is loose, that contributes to the ejection of the distributor, but it has to come out a good bit before the spring no longer pushed the gear down.
Because the slot is offset the distributor will only fully seat when the tangs are lined up correctly, but there may be a tendency for them to catch on the slot when ~180° out of alignment - that can cause erratic motion if you didn't truly get the distributor all the way in, much more likely than a damaged brass gear.