Rough idle turned to crank then ka-thunk

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71drtswnger

71drtswnger

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So i went from what looked like a semi common issue to one i can't info on. My dart was stuttering then dieing then would die at idle even while moving but only after warming up. I checked all the basics fuel, spark, distributor, battery voltage. But i couldn't find the issue but now when i crank it over it'll crank but stop with a thunk but if i take the cap off the distributor i can crank till the battery dies. So to me it seems like bad timing but I'm lost and don't want to cause more damage than might be there.
 
Post some photos of the inside of your dist cap and the rotor
 
Here you go

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Have you DONE anything to it immediately previous? EG the dist looks might clean is it new? Did you change the timing?

If you have not moved the timing I would attempt to check it. Sometimes you can pull the coil wire and leave it "lying" near the top tower so it has to jump spark. This sometimes will relieve the kick so you can check timing.

If you cannot do that attempt to check static time. Bump the starter and hand crank it so the timing marks are about where the timing should be. Examine the rotor tip does it point to either no1 or 1/2 turn away? And examine, the pickup coil core should be aligned with the reluctor tip

You may have broken a distributor drive gear or slipped a timing chain

I don't know about "all" but many slants use a plastic distributor gear
 
I replaced the cap and rotor when i bought the car about 3-4 years ago and never had issues till recently. And i did put the engine at tdc and the rotor is about a 1/4 turn from cylinder 1

Snapchat-73751576.jpg
 
Rotor looks a bit burnt or has had contact.

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And there's a bit of grease looking smudges on it and the inside of the cap.
 
The rotor and cap did have some "welding" marks but i didn't see it as a huge issue and my hands weren't the cleanest when i was handling it
 
I had a small block that developed a misfire on my way to work 50 miles from my house.

Nothing I did fixed it. Had it towed home.

At home with more tools and test equipment. Nothing to explain the problem.

I grabbed the original dist that had been in a box on the shelf since the 80s and popped it in. Fired right up and ran like a champ.

The dist I pulled had about 1/4" of up and down movement on the shaft the rotor sits.

I also noted the the rotor had a bad circle on the contact and the center pin on the cap was disintegrated.

I came to the conclusion the rotor was moving up and down enough to make and break contact to the cap causing the misfire.


Just something to look at.
 
Looks to me like it's time to pull the dist and inspect the drive gear. If that is OK time to evaluate the cam timing

Any idea of the miles on the engine or work that has been done?
 
From my understanding the engine had a teardown and rebuild abt 19 years ago and as for miles i can't be truly certain but it's been a daily driver since 79 and the odometer according to the previous owner rolled over 3 or 4 times
 
Well I'm gonna come around from the other side.
What if the engine flooded to a stall, and one cylinder happened to have a lot of fuel in it. That would cause the crank to go "thunk" trying to compress the fuel.
But as the engine sat, the fuel drained into the oilpan, and then it cranked fine.
Now, having washed all the oil off the cylinder walls, the tired old engine can't make enough compression to fire up on.
This explains all your symptoms including the original rough running.
I mean; what if.

If that is what happened;
the cure could be as easy as to fix the carb, oil up the cylinders, and probably to drain the oil.
 
Wouldn't i have had trouble starting (before the thunks started) due to the rings not being expanded and not creating compress due to gaps
 
Time to do some diagnostics. 1st, if the timing marks are on TDC, and the rotor points where it shows in the picture, and the wires are in the cap as the factory installed them (#1 being near the locating tab on the dist) the timing is way off.
I would pull the plugs, and move the damper back and forth while watching the rotor on the dist. See how far the crank rotates before the rotor moves. This will give an indication of the timeing chain condition. Also pull the dist and check the gear. If those look OK, time for a compression test.
 
In picture #6 with the welding on the tip of the rotor, I see black stuff on the top of the rotor. It could be a smudge, but it also may have tried to arc back to the distributor shaft.
 
Also don’t discount the magnetic pickup.
They can cause all kinds of weird things to happen.
Just because it makes a spark doesn’t mean it doing it when it’s supposed to.
 
Charrlie_S said:
Time to do some diagnostics. 1st, if the timing marks are on TDC, and the rotor points where it shows in the picture, and the wires are in the cap as the factory installed them (#1 being near the locating tab on the dist) the timing is way off.
I would pull the plugs, and move the damper back and forth while watching the rotor on the dist. See how far the crank rotates before the rotor moves. This will give an indication of the timeing chain condition. Also pull the dist and check the gear. If those look OK, time for a compression test.
Click to expand...
I thought slantys did not have chains
 
Demonracer said:
In picture #6 with the welding on the tip of the rotor, I see black stuff on the top of the rotor. It could be a smudge, but it also may have tried to arc back to the distributor shaft.
Click to expand...
On the blue any darkness is grease but the tip itself did have some carbon build up evenly across the tip but no sign of arcing on the contactor
 
Charrlie_S said:
Time to do some diagnostics. 1st, if the timing marks are on TDC, and the rotor points where it shows in the picture, and the wires are in the cap as the factory installed them (#1 being near the locating tab on the dist) the timing is way off.
I would pull the plugs, and move the damper back and forth while watching the rotor on the dist. See how far the crank rotates before the rotor moves. This will give an indication of the timeing chain condition. Also pull the dist and check the gear. If those look OK, time for a compression test.
Click to expand...
I'll have to give that a look but if all checks out how would i go about doing a compression test
 
TrailBeast said:
Also don’t discount the magnetic pickup.
They can cause all kinds of weird things to happen.
Just because it makes a spark doesn’t mean it doing it when it’s supposed to.
Click to expand...
I can take a look at that but i have a feeling that the dist is the problem seen as it is clock about 90 degrees from were it should be
 
71drtswnger said:
Wouldn't i have had trouble starting (before the thunks started) due to the rings not being expanded and not creating compress due to gaps
Click to expand...
I read the OP which states prior troubles.
However, my post, as stated, is
"What if."

And I said nothing about "rings not being expanded, and not creating compression due to gaps." That must be your interpretation.
The missing oil I am talking about, is to be
1) firstly, on the ring lands, sealing the rings to the pistons. and
2) secondly, on the cylinder walls, left there by oil-ring design, for the specific purposes of sealing the rings to the cylinder walls and
3) lubricating the working edges so the daym things last 100,000 miles.
4) the gaps are nearly meaningless in this grand scheme of things.
 
71drtswnger said:
I never noticed a plastic timing gear in my boredom searching I've done so that a new one for me
Click to expand...
Just to be on the same page, yes the nylon timing gear on the bottom of the Distributor shaft is known to crack, thru one of the Roll-pin holes. I've taken quite a few Ds out that were cracked in this way. It seems that when they get old, they get brittle.

As to timing chains and slantys;
I have never personally rebuilt a slanty. I usually just replace them with 318s lol. However, I have had in my lifetime, replaced two slantys with rebuilt units, for the specific purposes of increasing fuel economy. Unfortunately, I must never have been any good at tuning slantys, cuz all my tuned 318s got better hiway fuel-economy than even the best of my slantys, lol. Altho, there was this one hi-compression slanty that I had built for me, that could have maybe been a runner, had I tried harder........
 
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