318 Duster won't keep timing

I have a 1973 Duster with a 1968 318 engine. Here's my problem:

I set the timing according to specifications. I drive for a while then later when I try to restart the car, it won't start again until I have reset the timing. Once it is reset, it starts right up.

-I recently (as in a couple years ago) changed the timing chain
-The air gap for the distributor is in spec
-The engine block is a 1968 and is set for 1968 specs (this caused some frustration earlier)
-carburetor is new

Any additional suggestions from you guys on where to look for the source of this problem?

is the distrib clamp bolt tight? I cant think of anything besides this that would let the timing change.

I just checked it to be sure and it's tight..

Had an aspen w this problem. Several things I found- dist bushing had play, timing chain slack, slipping dampner, and worn cam. Every single time I drove it the timing had to be reset, so I got pissed and yanked the motor and replaced w refreshed one so I could drive car and diagnose engine out of the vehicle....got a spare laying around?

Also, every time I set the timing, it had to be set ahead, because once you tightened the clamp on the dist down, the timing mark would move. Actually watched it happen while friend tightened bolt.

Electronic ign conversion or are you meanin point gap?. If point gap next time (actually with either one) BEFORE you crank it see what the gap is & you might pull (& GROUND) the coil wire & crank it & see what the timing light shows for initial. Any possibiblity it ain't a timing issue & something else is causing this (heat soak etc). I would go over the dist innards from head to toe tho.

Is there any consistency in the amount of timing that is off? Is it retarded or advanced? Do you have to reset the timing no matter if the car is cold or still hot/warm? Last, have you ever checked the timing before you shut it off?

Is there any consistency in the amount of timing that is off?
Not that I can detect

Is it retarded or advanced?
The factory specification for 1968 is 10 degrees advanced. When the timing shifts after operation, it appears to be retarded. Because I have to advance it to put it back to spec.

Do you have to reset the timing no matter if the car is cold or still hot/warm?
The timing only shifts after it has been in operation, so warm.

Last, have you ever checked the timing before you shut it off?
I haven't tried that yet.

The car is electronic ignition. I've changed the cap and ordered a new distributor, hopefully this will help.

Vacuum disconnected when setting timing?

Check the gear on the distributor,is it tight?

gear on the distributor? There is no gear on a small block distributor, nor a big block for that matter. There is one on the slant 6 though.

If the gear on the intermediate shaft was loose, which is where the gear that drives the distributor is actually located, then the oil pump would be failing too. Has the OP seen oil pressure issues?

this deal ain't makin any sense, we're missing something here. I cant wait till we get to the bottom of whats going on

I stand corrected.
I should have stated distributor drive gear.
"it appears to be retarded. Because I have to advance it to put it back to spec.
This is with a timing light?How does it run when you start it with corrected timing and how long?
Distributor bolt is tight but is the distributor itself tight?

Good point, bolt could be bottoming out before the clamp tightens down on the distributor.

Other thing that's been floating in my head, and it's way out there, is a broken distributor shaft inside the housing.

If the shaft was broken I would bet it would be a whole lot worse,under acceleration or high rpm the timing would probably slip beyond runable.

Does your timing chain have all steel gears ? or the plastic coated ones ?

I've seen this happen once on a car where the intermediate shaft gear and the gear teeth on the cam were almost totally worn away.

Pull the distributor and look at the tang. Also pull the intermediate shaft and check for wear.

The vacuum is blocked when setting timing, so yes.

It is tight.

I agree, it would be undriveable if the shaft were broken.

The gears are all steel, no plastic.

The gear looks OK from what I can tell just removing the distributor. I have not had the opportunity to remove the intermediate shaft as that would require removing the cylinder head. This will probably be my next step if replacing the distributor doesn't remedy the issue.

I do set the timing with a timing light. It runs fine when the timing has been newly set. Once completing a short drive, maybe fifteen or twenty minutes, I stop the car and it will not restart. This is when I discover that the timing is again off. It does not do this every time, however.

How far off & which way? same amt each time when it does do it?

How are the return springs on the mechanical advance? Both in place? And is the shaft free-not rusted-stuck like?

My thoughts too. The only place where something like this would be likely to happen is in the mechanical advance mechanism.

R.

X3, there is no way what is happening is happening unless the distributor clamp is loose

A friend had this issue, the part inside of the distributor that is supposed to MOVE was stuck.

OP , take off the distributor cap and grab the rotor and turn it , it should move fairly easy a small amount and then spring back when you let go.

Agreed, twist it CW/let loose/see if it retracts all the way. Then as needed open it up & good visual inside

Have you determined if the distributor housing is itself moving under the clamp after your drive?

I did this and it moved fairly easily and sprung back into position when released.

It appears that the distributor housing is secure when the bolt is tight.


I have changed the rotor and cap. Tomorrow the new distributor will arrive and I will update the thread when I have completed this and tested it. I did drive the car today and upon running, stopping, and restarting the timing did not shift this time. However, as I said earlier it is sporadic.

with it being hit or miss it'll take some time to see if the new dist takes care of it. If desired send the old one to me & I'll figure out what was wrong with it & if you want it back just pay the shipping. On the new one you might note: what springs are in it, the # on the plate and the # on the can arm (& what the orig one had). EDIT when the timing does shift, how much and which way ???

When the timing shifts, I have to advance it to put it back in spec; so it is retarding when it shifts. At this point, I honestly couldn't say that it shifts an exact amount each time consistently, only that it is sufficient to prevent the car from starting.

Ok so on the occaision when it wont start you turn the dist a slight bit CCW then it starts & then when it starts & you check it with your light & the marks are where they were before? (Marks the same as the last time you checked/reset it?)

Did you guys miss this one?

Sounds to me like either the dist has surface depressions where the hold down sits, or something isn't as flat as its suppose to be. As he tightens the hold down, its pulling the dist back to where someone really cranked the hold down to.

I had a 360 one time where the block at the distributor was not cut flat. Every time you set the timing, and tightened the clamp, it would return to the original setting. I ended up replacing the dist, the hold down bracket, and making a soft shim for under the dist!

Even after that, the idea the timing is retarding itself enough for the motor not to start is something I'm having a hard time dealing with. I suspect there has to be a timing chain issue. I've dealt with that before as well, but that is a story for another time. Gene

Gene I did! I was wondering what kind of voodoo we was dealing with

I saw that but it was somewhat confusing to me.

Why would someone set timing, lock down the distributor, see that it moved and leave it like that ... assuming he even checked it afterwards?

He did say he changed the chain a couple years ago in the original post ... or did you miss that ??? ... so unless he put a crappy chinese piece of junk in there, or has driven 100k miles in that last 2 years, then the chain may not be the issue ... but stranger things have happened.

I saw that. I can think of very few things that can retard the timing on a running motor enough that it won't start, short of a timing chain.

Guess that brings up the point that the issue might not be ignition timing at all. Maybe he has a defective lead between the dist & the coil and the act of moving the dist is moving stuff just enough its making connections again. I suggest he look at the wiring where it enters the dist and be sure its not shorting to ground at the connection. A different dist would cure that issue. When it won't start, does he have a spark?

The issue may not even be ignition related at all but could be a low oil pressure issue that cranking the motor is temporarily solving. Gene

Rusty don't even think about vacating without informing us what it ends up being!

Ha Ha! As soon as I get more info, I will be posting in the thread, don't worry!

-RD

Have you checked to see if the guts of the distributor are loose? We know the shaft is working. You need to check the pickup coil.

Also, clamp that thing down and don't let it move when you tighten it.