Valve Timing on 67 Mustang with 289

A friend of mine overhauled his Mustang and at times it idles smoothly and at other times idles rough. It has a valve job, bearings, rings, points, condensor, cap, wires, plugs, rotor etc. Vacuum during cranking is 2 inches and 16 running which seems low. He did not replace the timing chain as he said the marks on the sprockets lined up and the chain wasn't excessively loose.

The intake pushrod just starts to open when the mark on the balancer is at TDC. This seems late to me. The Ford manual does not give a spec.

Why does it run smoothly sometimes and rough other times? We tried a known good carburetor and coil to no avail. What are the symptoms of a chain that has jumped one notch?

...if he's a friend of yours, he's no doubt an imbicile and shouldn't have been messing with the engine in the first place.

You may want to check the distributor shaft bushing, if it's loose and wobbles, the ignition points have a tendency to be unstable. grab ahold of the rotor after the cap is off and see if she wobbles.It may not be the problem, but if everything else was done and this may have been overlooked...I have a 67 Mustang project too. But mine is in a hundred pieces. Best regards!

By noting the position of the timing mark on the damper vs. the position of the pushrod, you have documented a timing problem. Now you have to determine whether the damper ring has moved [and the relationship between the pistons and the valves is actually correct], or whether there is a problem in the timing chain.

To determine whether your timing mark on your damper is correct, Google "positive stop method" + "TDC"...this will determine exactly when your piston is at TDC, and whether or not there's an error in you damper timing marks. If there's an error, these guys can repair it:

http://www.damperdoctor.com/

Then with a correctly marked damper, check where your intake valve is in relation to TDC. If your cam still appears to be significantly retarded, tell your buddy that he needs to suck it up and replace the timing chain and gears.

Anytime you do an overhaul on a smallblock V8 and don't replace the timing chain and gears, you're doing a "half-fast" overhaul, and are at best postponing the day when the engine will let you down. Is the price of a chain and gears worth bent valves and pushrods, or perhaps sticking a valve through a piston top? Call it insurance, replace the easy stuff, and walk away KNOWING that those parts are good, rather than guessing.

P.S.: The poor vacuum readings are a sure clue that the valve timing is off, Sherlock.

Buzzman,
Thnks for the reply. I have already found TDC on the balancer. When should the 67 intake open? Is this measured with .050 lift or something less. Why would it idle smoothly sometimes and not others? Is the 289 free wheeling or will valves hit pistons in it?

I find it tough to believe that an engine that needed an overhaul didn't neet a cam drive. Most later model 289/302's would have had nylon top sprocket

Fords used to be REAL bad for slipping the damper. DEFINATELY make yourself a positive stop out of an old plug, and determine TDC. VERY easy

You install the stop, and gently wrench the engine around until the piston hits the stop, then make a temporary mark under TDC on the timing tab onto the damper. Then rotate the opposite direction until it stops again, and make a second mark under TDC This will give you two temporary marks, and TRUE TDC will be halfway between.


Also, late (ignition) timing or a vacuum leak can cause low vacuum.

Tom 43, mine runs like that and I have replaced the timing chain/sprockets and damper and lastly, the distributor. I've come to the conclusion that it's sticky valves. Doesn't do it running down the road.

EXCUSE ME!!

If you can't behave yourself, then just GO AWAY!

Finding TDC on the marks on the damper is different that using a positive stop to find TRUE TDC. And I only threw that tidbit in because you want your point of reference--TDC, in this case--to be accurate, in order that your conclusions about the problem will also be accurate. If TDC on your damper is 20 degrees off from true TDC, using the damper-indicated TDC mark for a reference point will ALWAYS result in inaccurate results.

And most of us know that, at TDC, BOTH the intake and exhaust valves for that cylinder should be closed. ANY other outcome is evidence that the engine is out of time [cam timing, as opposed to ignition timing]. While radical cams that cause "rumpy-rump" idling will have more overlap than a stock cam, by TDC even the most radical cam should have both valves closed.

As far as using a dial indicator and a degree wheel to determine whether the intake valve is opening where it should, unless you have the manufacturers' spec for that particular camshaft, you're only guessing. Even if the engine is "stock," the 289 hi-po [271 HP] engine used a different cam than the standard 289...so without knowing exactly what cam is in the engine, you're just urinating in the wind.

And using a degree wheel and a dial indicator is basically useless, if the timing chain and gears are suspect...primarily because the results may not be repeatable on a consistent basis. Sounds like you've read a HOT ROD or CAR CRAFT magazine sometime in your life, but only vaguely understood the subject matter.

EGR or brake booster intermittent vacuum leak.

At TDC on the non compression stroke, the exhaust valve will just close and the intake will just start to open on an engine without a wild cam in it. If the intake just starts to open at TDC and the Exhaust valve just closes, the mark on the damper will be in the right place. Check the EGR or the dist. advance.

hmm..intermittant ? Well first thing I'd do is verify TDC on balancer . YOur intake valve opening is of no concern , unless you are degreeing a cam . Once TDC is verified . Check ignition timing , watch it, does it change as engine idle goes into it's fits? If so check dist bushings. I have seen some valve adjustment problems on these . If you are on the edge of the adjustment limit it may be hanging a valve open slightly , would account for low vacuum and rough idle . 16 inches depending on the cam is not out really terrible . But if it's all stock, could be higher . I've raced small blocks for years,if it was here in shop I'd have it figured out in less than a six pack ! lol What year is this motor ?

Tom, intake opening should be (start) at about 36 degrees BTDC. However if cam timing were the issue it would be a constant problem. The issue is most likely a sticky advance plate, or sticky weights. Good luck Dave

....you don't know Tot4.3 very well. He put the jerk in jerkoff

Talk to me baby! I LOVE it when you misspell words like "imbecile".

Not likely cam timing of the problem comes and goes. What the guys say about sticky / worn ignition parts sounds likely.

Thought I would share the goofy situation I ran into on a relatives 302 Maverick.

He had that short lived aluminum / nylon cam sprocket that shed all the nylon and slipped the chain retarding the cam.
He replaced the timing set and could hardly get it to run, hard to start and would stall at low rpm. I told him he had to have installed the new timing set 1 tooth retarded, because thats exactly how they run with late cam timing.
He absolutly swore he had double checked it and the marks did line up.
I thought "yeah right" and tore the front of the engine down in my shop.
THE MARKS WERE LINED UP!!!, but something about that new cam sprocket looked odd.
Normally on a SB Ford cam sprocket you can draw a line from the center of the sprocket, through the dowl pin to the mark on the edge of the sprocket. On this one, the line through the sprocket center and dowl hole missed the mark by 1 tooth !! The guy who drilled the dowl hole at the factory got it 1 tooth off in the drilling jig !!.
Other than that, the sprocket was perfect, so after comparing another old Ford cam sprocket to make sure I was right about the cam,dowl pin and crank all being in the same line, I reinstalled the misdrilled new sprocket 1 tooth off from the indicated mark. It ran perfectly, ran that way until it wore the car out.
Normally a guy doesn't think to look for crap like that, but it did happen, atleast once. :0)

....is that the end of the world? Glad for you that you recognized the PROPER way to spell it. Must be from reading it on the diagnosis from your doctor.

very common on higher mileage SB Chevys. I drove a ford school bus that had the same issue, pionts would close and she'd backfire when they opened back up. Kids loved it

While I agree that politically, ttt is an imbecile, here is not the place to point that out. If the thread was started out as OT, then the derogatory comments about ttt's politics, orientation, lifestyle, etc would be pertinent to the conversation. But since this started out as a question about ignition, timing, or whatever the problem at hand is, I will confine my remarks to that subject: Check out the distributor, carefully, look for slop in the bushings, make sure the drive gear is intact, and the pin that holds it on the shaft is tight, too.