I was timing my engine the other day, and I noticed that the timing mark was varying 3-4 degrees from where I set it. The engine was at idle (~700 RPM) with vacuum advance disconnected and the line from the carb plugged. I set timing for 10 BTDC as best I could, but the timing mark was varying between 13 and 7 degrees.

I've never really seen this before... What should I check? Or maybe it's my timing light?

Thanks.

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- Dan in Simi
'74 Dodge Dart Custom

hello,
you might not want to hear this,but sounds like a worn/stretched timing chain. pretty common on high mileage engines.
Anybody got any other thoughts?

regards,Rod

What (exact) distributor are you running?

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一期一会
Too many people who were born on third base actually believe they've hit a triple.

Just reading the heading before clicking on it I was thinking timing chain. I'll second that diagnosis. If 10 people can give the same conclusion, then it must be so.

To check to see if your chain is good or bad, remove the distributor cap. Turn the engine in the normal dirction to where your crank timing marks line up to TDC. Then turn it in reverse direction while watching the distributor rotor (with the cap off of course). As soon as you see the rotor start to move, stop rotating the engine. Look at the timing marks. This gives you the slop in crank degrees.

If it's under 6*, chain is probably still servicable. If it's between 6* and 8*, the engine probably still runs accepbably, but you should replace it. If you have over 8* of slop, you'll wonder how it ever ran after getting the new chain installed.

Get the chain and gears. The crank gear will require a puller to remove. Many of the slants got the silent cam gear with the plastic teeth. They were junk and prone to failure.

Mike

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Recognized by US Federal Courts as a Fuel Economy Expert!

A sloppy timing chain can certainly cause this symptom, but it is not the only thing that can do it, so let's figure out exactly what's going on before you start buying parts and taking stuff apart, eh?

A broken or missing distributor mechanical advance spring, or the single flimsy spring that comes in the Mopar Performance distributor, or a worn point cam on a points-type distributor, or a wobbly distributor drive pinion, or a distributor drive pinion installed with too much end play, will cause the timing to bounce around at idle. Much easier to repair or replace the distributor than to do the timing chain.

MPGMike's test for timing chain slop (watching the distributor rotor as you rotate and counterrotate the engine) is a good one.

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一期一会
Too many people who were born on third base actually believe they've hit a triple.

I saw the same thing exactly on my 1980 Aspen - even after I installed a Cox steel timing chain set. I replaced my distributor with an OEM new, not rebuilt - unit and this went away completely. Had you asked me before, I would have told you it was probably my timing chain. However, my timing at idle always varied a few degrees, even when the car was new. So it may very well be excess play in your distributor.

Mitch

Thanks for the tips - I will try MPGMike's test tomorrow and proceed from there.

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- Dan in Simi
'74 Dodge Dart Custom

Another test to do (while you are coming up with the answer to the question of what distributor you're running, which has now been asked and gone unanswered three times...so how 'bout it?) is to grasp the distributor rotor and twist it firmly clockwise. You should encounter light and then heavy spring tension, with a definite "detent" feel at the start of the heavy tension, and the rotor should spring briskly back to its original position when you let go.

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一期一会
Too many people who were born on third base actually believe they've hit a triple.

I didn't know there were different types of distributors; I assume it's the stock distributor for a '74 model. It does not have points that I can see; it has a magnet and a 6-splined cylinder for the stock electronic ignition.

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- Dan in Simi
'74 Dodge Dart Custom

yes, but i think he is looking for a tag number.

sb

Trying to turn the rotor by hand, it will turn clockwise only a few degrees with little to no resistance then it will stop turning, even with considerable force. So I guess I may have found my problem.

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- Dan in Simi
'74 Dodge Dart Custom

Yup, you might have found the problem. Sounds like you might have a broken mechanical advance flyweight spring. "Bump" the engine with short bursts of the starter motor or turn it over by hand until the distributor rotor points straight up (12:00 position), then remove the hold-down bolt and pull the distributor out of the engine. You can then easily remove the pickup plate and carefully inspect the flyweights and springs. Can't recall whether the toothed reluctor needs to be removed from the distributor to remove the pickup plate; if it does, it simply pries upward with two screwdrivers. You will need 0.006" and 0.008" brass (nonmagnetic) feeler gauges to set the pickup-to-reluctor airgap on reassembly.

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一期一会
Too many people who were born on third base actually believe they've hit a triple.

I'm pretty sure it does need to be removed. But, I thought there was a clip on the shaft inside the reluctor, that you have to use a skinny needle nose to yank out, before you can slide the reluctor up? Theres also a small metal dowl pin there, don't loose it. There are screws on the side of the housing for the advance pod and for the plate.

Yep two screws on the side of the body to remove the vac. adv. pod (use screwdriver to gently rock the pod arm out of its hole in the pickup plate, then two more screws to remove pickup plate, but you have to use two large slotted(not phillips head) screwdrivers to gently pry up on the reluctor and don't lose the dowel pin...the hairpin peirre refers to only needs to be removed if you intend to remove/replace/modify the governor plate... you can still easily swap springs using a scratch awl or probe and some dexterity without removing the governor or the weights from the body...


-D.Idiot



Now oddly I tryed to do this exact thing on the 1973 distributor in my Valiant, the lightly springed distributor in the Hpak duster, and the stock supersix distributor in my parts pile, and couldn't get any of them to do what you say it should do, until on one parts distributor without the vaccuum advance pod installed it was slightly easy, then really tough then it snapped right back again...

Good advice.
My timing mark was dancing around at idle too. I wasn't losing sleep over it but I had the motor out last weekend anyway to change the rear main seal and changed the timing chain while it was out.
It still dances. (the original chain was worn so it wasn't for nothing)
I guess I'll check out the distributor using the recommendations in this thread.