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Discussion Starter #1
Hey all,

I was pulling up to the house the other day, just coasting it in, 2nd gear, clutch engaged, no throttle, when all of a sudden I hear a ticking/popping/rattling noise. Now it wont idle without a little throttle, feels like its missing a cylinder, and I'm getting a very consistent "pop pop pop pop pop pop" from the intake/carb. Its not a sporadic backfire, like its coming from multiple cylinders. Its definitely RPM related, and gets much louder (like gunshots) under load or a small rev. Sounds like its coming from the same cylinder, in my inexperienced opinion.

What do you good people think the issue is?

I advanced and retarded my timing a few degrees (well, i actually just turned my distributor back and forth a bit) and the popping continued. Keep in mind that the engine was running normally before this happened while I was driving. It would be pretty difficult to accidentally cross plug wires while the vehicle was moving:winks. I would hypothesize that there is a burnt valve, or broken valve spring or something, right? It was a warm day, about 112 F, and I was probably driving home in lower gears (last day of school, I was excited) than necessary. The only other thing I can think of is that my carb runs really rich, but its never been a problem. Just smells sporty.

If I did burn a valve, how difficult would it be to just ditch the old heads for a refurb pair of GT40s? Or even (please don't hate me) a pair of those cheap Chinese heads? Can I do it without removing the engine? Am I looking at new cam, pushrods, rockers, and lifters? Or would you just suggest a valve job? Keep in mind that I want to learn about the car, but I'm young, have little money, and Its my daily driver.

1966 Coupe
289
4 Barrel Holley
Edelbrock single plane
nameless HEI ignition (works pretty well)
longtubes
Toploader 4 spd

Thank you so much in advance.
 

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Hi,
Have you removed the valve covers for a peek at the valve action (engine idling)?
Are all of your wires in good shape (cross-fire?)?
Have you a vac gauge to check the engine vac at idle? If not, get one. hey can reveal a number of engine maladies.
Yes, the heads and cam can be changed with the engine in the car.
Good Luck!
 

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Hello Rycallahan,
You are very fortunate to have 2 GREAT responders on this.
These guys know what they are talking about.

Very likely a valve related issue as they mention BUT
I like to start with the SIMPLE stuff before going to far.

I would double check and make certain the wires are attached to the distributor
cap and the spark plugs. you would be surprised at the little POPPING sound
that can come from a spark jumping from a loose wire on the cap. They MAY look seated BUT make certain they are all tight.
THen after checking the SIMPLE things - -likely time to look under the
valve covers as suggested.
Seems ODD that things would start that suddenly unless is was a simple
issue like a plug wire loose or off.
Just my 2 cents BUt please continue to post and we can provide more
ideas.

Print Dad
 

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Discussion Starter #5
I really appreciate the replies, everyone. I agree with Print Dad in the fact that one should always start off simple. I will start off by taking a look at the condition of my ignition system.

Kenash, you mentioned crossfire. My entire ignition is only about a year old, but I heard that if the wires are positioned wrong, they can set off each others spark plugs. What a concept! This is induction crossover, correct? How can I check for this? Will holding the wires in different positions diagnose the problem? The ignition does tend to look like a dead octopus sitting on the engine.

Thanks again, everyone.
 

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Take it one step at a time and the simple things first as stated above,,you can check to see if your wires are jumping spark by looking under the hood at night while the car is running,,move the wires around a bit at the same time,,
 

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Agreed...1st check the ignition system (including ensuring the rotor has not detached itself from the shaft) and if all is well, timing chain....sounds like it stretched and jumped a tooth or 2...
 

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When an exhaust lobe goes flat you will get a pop back through the intake tract as the exhaust can't get out any other way! Or an exhaust rocker arm broken, stud broke, pushrod bent?
 

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Discussion Starter #10
It's a bent pushrod. Now what?

Well everyone, I checked all the "simple" stuff, and found nothing. So, I pulled off a valve cover to find that the #6 exhaust rocker had removed itself from its valve. The pushrod is completely bent, right were it contacts the rod guide. Valvetrain looks completely stock, although the springs may not be.

The tip of the valve looks a little mangled for obvious reasons. What would happen if I just stuck a new pushrod in and set it back up? I know it would wear out real quick, but lets talk hypothetically. Does anyone know the stock pushrod length for a 1966 289? Im not super excited about removing the head(s) out here on the street with the dust and heat.

Anyone have any solutions or advice?
 

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I would put it back together with a new pushrod and try it. it could be as simple as the nut backed off of the rocker arm and went south from there....
 

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If you didn't hear any valve clatter before the problem and taking into consideration that a push rod/valve seems damaged, I would check to see if the timing has slipped. Remove the cap and check no. 1 cylinder in relation to roter position. Mine slipped once and I bent three valves.
 

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Burnish the top of the valve stem, at least and don't expect it to last. Pull one of your other pushrods and measure that. Expect to do a valve job soon. Unless the rockers were loose, you may have something else going on that bent the pushrod.
 

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Discussion Starter #14
Too much damage?

Thanks again for the replies. Every single one of you has been helpful. I love these forums!

Heres are some pictures of the valvetrain right after I removed the valve cover. I know its hard to see, but the tip of the valve looks a little "smeared" off to the side. there is also an oval shaped wear pattern on the tip of the rocker that extends off the side of it. Does this look too damaged to salvage temporarily?

IMG_1742.jpg

IMG_1746.jpg

It aint pretty like I'm sure all your motors are, but it was working pretty good up till now.

Another issue was that after I was checking the ignition, it just flat out refused fire any cylinders. There was is still a spark on the wires I checked. This is strange because it was running even with the down cylinder. This could be due to messed up valve timing, like some of you have mentioned. Also, is it strange that all the valves in this bank appear to be closed? No? Oh well, Ill figure this one out after the valve issue is remedied.

Thanks again!
 

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Is that a groove worn into the rocker arm shaft?

If so, it has to be replaced and it is pressed in. (May be time to pull the head and head for a machine shop. You'll more than likely have to do it to replace the valve anyway.)

Also, you state it's a 66 mustang, but those heads look like 65 heads since there are small pushrods holes (which require hardened pushrods) and the rockers themselves are not rail-type rockers.
 

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Discussion Starter #17
Interesting observation. I'm not sure if that groove is intended to be there or not. It looks pretty clean to be worn in though. What holds the rocker off the top of the stud boss? Is it the shoulder at the base of the threads on the stud?

The engine was rebuilt one or two times, the details of which I am unaware of. It could have taken on a different cylinder head somewhere.
 

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Discussion Starter #18
This sure looks like a classic case of a slipped timing chain.
Jetjock, what kind of damage or signs should I look for as symptoms of a slipped timing chain? Its interesting how only one valve would take damage. I will be sure to see if I can check my valve timing.
 

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Jetjock, what kind of damage or signs should I look for as symptoms of a slipped timing chain? Its interesting how only one valve would take damage. I will be sure to see if I can check my valve timing.
It's happened to me before. My chain slipped and punched a couple of valves. You can easily check it out by marking on your distributor where no. 1 and no. 6 are. Remove the distributer cap and turn the harmonic balancer clockwise until the timing mark is at TDC and see where the rotor points. If it's not in the region of one of those two cylinder marks then you timing has slipped.
 

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ryan, get a pushrod,(go to autozone and get a melling MPR-279) install it, adjust the valve, crank it. and BTW, it does NOT need to be a hardened pushrod! ;)
 
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