Stretched timing chain causes ignition timing problem?

In one of the fairly recent Car Talk podcasts the caller had a 69 Ford Mustang w/302 v8 and 2B carb. Engine was misbehaving, stalling at idle. Warm/cold no difference. Carb tested good, choke function tested, good. I was interested in this topic b/c the engine is the same configuration as my truck. Ray said the problem could be that the ignition timing was out of spec.

The caller asked how that could happen as the timing was set 2-3 years ago at the last tune-up. Ray said its b/c the timing chain has probably stretched.

I can see how a stretched timing chain could affect the timing, b/c the timing chain drives the camshaft, which drives the distributor shaft, which drives the ignition point breaker cam. But I wouldn’t haved guessed a stretched timing chain would be the most likely cause for out of spec spark timing for this caller. My thinking is that if the timing chain was gonna stretch, that would have happened years ago. I’d have said the more likely explanation is the breaker point gap has changed (due to wear of the surfaces of the points contacts or that little plastic thing that rides on the breaker cam), and that dimensional change has caused the the points to open later or earlier than when it was set at the last tune-up & a resultant ignition timing change.

Which do you folks think more likely for ignition timing change for v8 engines of this era, stretched timing chain, or change in the breaker point gap?

When we are talking about cam in block engines like the 302 small block Ford timing chain stretch has never really been a issue over the years. It is since we switched to overhead cam engines that problems started to arise with timing chain stretch, but as anything in the automotive world. Anything is possible!!

On a carbureted engine you need to remember that there are two different types of timing going on with the engine. Mechanical timing which is set when the timing chain is installed between the camshaft and the crankshaft. Ignition timing is adjustable at the distributor, this is the timing that is normally set when mechanics are “timing” an engine.

Anyways regarding the timing issue, you have some great observations. My first check would be to check the points and condensor. These items are considered wear items and need to be replaced fairly common. If you have an engine like this I would suggest upgrading to an electronic ignition to eliminate these troublesome components.


First thing I’d check is the points, cap, rotor, and then set the timing. Make sure the vacuum and centrifugal advance works. If all that’s good, and the carb’s in tune, then check for a stretched timing chain.

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Informative post, thanks. I think Ray was referring to ignition timing (rather than mechanical valve timing) b/c he suggested the caller take their Mustang to a shop and check the timing w/a timing light.

Ray did ask the caller about the condition of the points, condenser, dist cap, rotor, & high voltage wires. Caller said they were all ok.


But the plastic teeth on the cam gear were notorious for wearing down causing timing problems.

And if you were lucky, it was caught before the plastic pieces falling into the oil pan clogged the oil pump pick-up screen and starved the engine of oil.



Good Point!! Thanks for the correction on that!

Tom said the 69 Mustang was a dog. Not sure why, I’m presuming he didn’t mean to insult my truck … lol … If the 69 Mustang was a dog my truck is even more so, b/c the emissions changes to the design results in major power losses for the 302 between 69 and early 70’s

Retarded cam timing from a stretched chain would sacrifice a bit of low end torque. The ignition timing could be easily set back into spec and maybe even advanced a bit beyond factory spec to compensate somewhat.

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The 69 Mustang got fat. Heavier and a bit larger than the 64 to 68 cars. The 302 cars really needed a 351 to compensate for the extra flab.


Had a 68 cougar with a 302, bought a dwell meter to set points, as points being off in my experience affected timing.

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I can’t speak to a stretched chain but I did have the sheared plastic timing gear though, and yeah pan had to come off too. The other thing though, if the rubbing block on the points was not lubed at install, the block would wear down and screw the points up. Even back then people missed it from time to time so maybe now it would be even worse with people unfamiliar. You got a little pill capsule with grease in it and may not know what to do with it.

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Yep, points cause problems, new ones that are correctly adjusted are the first step, then set the timing, which is directly affected by the points adjustment.


I have had some old Ford V-8s and they weren’t even that old then. They would eat plug wires. The boots would get as hard as rock and would crack. When we changed the wires the engine would not shake or stall. The worst case would be trying to drive through a big puddle with bad wires. A 74 with a weak ignition module (boxy thing) and bad wires would quit and have to dry out before it would start. A stretched timing chain would have no effect on how it would run. On a 69, nothing you would notice.
Cold or hot? Really bad wires. Changing them is always the first step and make sure the plug near the stove is not three times older than the rest of them. Some people are reluctant to replace that one. I have removed the thing to get a new plug in there and then put it back on. It may be different on a 69.

My back plug had a shroud attached to lessen oil fouling. Was blocked off with crud. Had to remove riser assy to get plug out.