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Timing mark jumping around

Dartman72

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Working on a 1967 Dodge Coronet RT clone. It has a 440 with Chrysler electronic ignition. Its my buddy's car and he has had for 20 years and never done anything to it. Previous owner rebuilt the engine but we don't have any specs for timing. I put new plugs, wires, rotor cap etc. I didn't know what it was timed to so before moving anything I put my timing light on it to get a bench mark of current time. At 3500 RPM with all the advance out it looked to be 25 BTDC. The problem is the timing mark jumped all around. I'm used to seeing the timing mark in a steady position. The light would be at mark and then jump 20 or more degrees and just kept cycling this way. I really don't have confidence in my settings. I can't get the light and mark to simply stay on position. The engine seems to run OK but I've struggled to get it timed and running right ( idle under 1000 RPM / easy start after hot). To get to idle properly I advanced to 36 BTDC but that appeared to much as it was difficult to start after warming up. I've backed it down to what I think is 32 Degrees. My question to this group would be 1. Why is the timing mark jumping around and how do I fix? 2.How do I determine proper timing for this 440?

Thanks
 
How loose is the hold down clamp when you're revving it? Should only be "loose" enough to adjust the timing, meaning still snug, but not loose enough to move on it's own.

I'd check that first, but aside from that could be a possible balancer issue.

At idle, stock(ish) 440's often like somewhere between 10-18 BTDC, 34-36 all in at 3000rpm. I'd set it to 36 degrees with a dial-back type light, while revving to 3000rpm, and whatever the timing is at idle is your base.
 
Check reluctor wheel has no movement or is canted on the main shaft. Also if you have dial indicator check for run out. Many articles on reluctor wheel issues. Secondly are springs on advN e shot or one is broken off?
 
Encountered what I determined as a carbon-clogged valve on mine causing a weird vacuum reading and timing light flutter. Got lucky maybe, trying the trick of old marvel oil to the oil and fuel running it for a a hundred miles or so..
 
Distributor shaft bushings causes shaft to wobble and timing to change. Snake oil sounds like he said same thing.
 
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May not hurt to check the timing chain for slip if all else fails. The others have posted something to look at,chain slop can cause problems. Keep us posted .. very curious.
 
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If you have to replace timing chain, use a double roller one from a reputable supplier. They do not stretch as much as factory one, keeping your engine in proper tune. Stretched timing chain is most common cause of fluctuating timing. It is possible that someone has installed centrifugal weight springs that are too light in the bottom of the distributor.
 
and then there's the infernal nylon teeth on the cam sprocket.
 
36* of idle timing suggests a cam of some duration/overlap. And it is NOT excessive if that is what the engine wants. There are different ways to get the reqd timing. The easiest way is to use manifold connected vac adv with an adjustable VA unit with the spring set to the softest setting [ Allen Key fully CW ].
See MVA benefits below..

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I had the same thing...the timing was jumping all around. I had my original Mopar distributor rebuilt by a member here. I touched nothing else. It solved it 100%.
 
OK lots of stuff to explore here - thanks! I'm going to start simple and move on from there. So distributor first. I'll pull that and make sure things are good - may just replace. I get the sense that the problem is electrical or electrical variation caused by mechanical movement. The timing light just cycles from right on mark to 20-30 degrees off mark consistently. When I rev the engine the mark moves but the cycling continues and moves with it. If I didn't have the timing light on it you'd have no idea it was doing that. The engine seem steady and smooth it's just the D**** light is jumping around giving me no confidence in my settings.
 
Pull the cap and twist the rotor see if it moves. It should , once you let go see if it snaps back to position.
Also like posted above try to move the distributor shaft side to side.
Also put a socket and breaker bar on the harmonic balancer bolt.
Turn the engine a small amount and see if the rotor turns at the same time. If you have a decent chain it should.
Just for the heck of it toss a different timing light on it.
 
Have to ask check the reluctor gap on all 8 points? The upper shafts bend alot.
 
Check the damper to tdc.
My mechanical advanced springs were very worn causing similar problem.

I did replace with a new dizzy and timing was dead on.
 
Any chance you are using a dial back timing light? Notorious for this issue.
 
You might want to check the harmonic balancer. Old style balancers had a bonded polymer insert. With age, the insert will deteriorate and flex or even separate causing the inner and outer pieces to shift. One quick way (although not the most accurate) is to put a socket on the crank bolt and turn the crank slowly. Make sure your belts are tight. You've got to get a good close view of the balancer. If the polymer is weak, you should notice a slight difference between the inner and outer piece moving in unison.
 
Working on a 1967 Dodge Coronet RT clone. It has a 440 with Chrysler electronic ignition. Its my buddy's car and he has had for 20 years and never done anything to it. Previous owner rebuilt the engine but we don't have any specs for timing. I put new plugs, wires, rotor cap etc. I didn't know what it was timed to so before moving anything I put my timing light on it to get a bench mark of current time. At 3500 RPM with all the advance out it looked to be 25 BTDC. The problem is the timing mark jumped all around. I'm used to seeing the timing mark in a steady position. The light would be at mark and then jump 20 or more degrees and just kept cycling this way. I really don't have confidence in my settings. I can't get the light and mark to simply stay on position. The engine seems to run OK but I've struggled to get it timed and running right ( idle under 1000 RPM / easy start after hot). To get to idle properly I advanced to 36 BTDC but that appeared to much as it was difficult to start after warming up. I've backed it down to what I think is 32 Degrees. My question to this group would be 1. Why is the timing mark jumping around and how do I fix? 2.How do I determine proper timing for this 440?

Thanks
Check the weights and springs inside the dist and put a little lube where the weights ride
 
Good idea thanks. I'll try in the spring when I get back to the garage I love :) - suffering through the winter where the sun shine's and the golf balls disappear on a regular and frequent basis!
 
If you can find someone with an old Sun distributor machine you could have them test it out of the car. Isolating it that way will tell you if it’s the distributor or something with the engine. Too much end play or sloppy bushings in the distributor will cause timing variations, so will worn or sticky centrifugal advance components.
 
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