Engine: 259 Engine 'shudders'

[(S)]

Working on a '62 259 with an Auto Trans. It has sat a few years with no air cleaner. Owner said it did run... I assumed at the worst a compression check would show a rusty valve/ valve seat or something. It does run, but something is not right, it shakes and vibrates, so we tried the following:

Intake runners were not rusty, changed the intake manifold to be sure. inside the valve covers were clean.

Checked the fuel system/ new filters flushed the tank, checked the carb, even tried a spare. Checked for vaccum leaks, checked for proper voltage at coil. new points, Adjusted valves, ran compression checks- all were right near each other, checked for excessive crank endplay, checked the flex plate....

We did do spark plugs and wires. After one test run we did see 2 plugs were white/yellow more than the rest. The car runs ok, no signs of burning oil or water.


I have seen one run kind of like this, but it had a tapping noise due to a backed out pinch bolt. This feels more like something way out of balance like a miss fire, but we did do a lot of checking for that.

Any suggestions would be a good. Plans are to tear it down, and check it very carefully, for proper clearances, rod orientation etc but tips are always helpful.

[RadioRoy]

The spark plug wires for number 3 and 5 cylinders should not be run where they look like they should logically be run. That's to eliminate crossfire. It may not be as much of a problem with modern wires, but it was with the old wires.

The plug wire that runs alongside number 1 should go to number 5. Likewise, the plug wire that runs alongside number 7 should go to number 3.

[(S)]

We've done quite a few, the routing is not the problem in this case..

[PackardV8]

New cap, rotor and condensor?

jack vines

[64Avanti]

You didn't mention the results of the compression test. Crossed plug wires?

[doofus]

How does it run if simply revved up or held at steady 2000 rpm?noises? try removing a plug wire, one at a time to isolate a single cylinder while running.is all this happening while in gear or neutral? try putting in gear and holding brake then giving gas to 4000 momentarily (Stall Test). Luck Doofus

[doofus]

How does it run if simply revved up or held at steady 2000 rpm?noises? try removing a plug wire, one at a time to isolate a single cylinder while running.is all this happening while in gear or neutral? try putting in gear and holding brake then giving gas to 4000 momentarily (Stall Test).how is coil polarity. could be bad resistor wire. Luck Doofus

[t walgamuth]

Sticky valves are a possibility.

[Mrs K Corbin]

Does it pop?

[JoeHall]

Valves too tight. Likely the exhaust valves are closing up. Adjust the valves, and set the exhaust valves on the loose side of the specs !

[jackb]

"Sat for a few years"... ?? Anything is possible, especially with an open intake..... Had similar symptoms with a 41' Commander. What does the oil pressure look like ? Mine would peg 70+ lbs at startup, then idle @ 5lbs. After a several starts, the rumbling would go away, then after ~ 8-10 startups, gone completely. Ended up using 1 qt / 100 miles. Did a complete rebuild...

[StudeRich]

I think I have narrowed this down to a very off center Converter Housing, a Con Rod backwards or on the wrong side or some "other" out of balance condition. Vibration Damper Pads are there and in tact.
We are about out of ideas on this one.

It is as found, so you never know what the poor little Car has been through, but we have done our best to check the logical causes.

However I have never had one with the Rods miss-assembled or tried to do that to know if it is even possible, but if it IS it sure WOULD Vibrate a lot like this one.

Valves are all at .026 Cold, compression is a very even 120 P.S.I. which IS about 20 Low, for a '62 259 but consistent.

Most all tests have been done in Park, the idle is relatively smooth until about 1200, just off idle when it starts dancing.
I am pretty sure a loose Front Engine Mount would not shake that much without some internal out of Balance condition.

[50pete]

what's the vacuum like? had worn cam lobe once, thing shook like crazy!

[GrumpyOne]

Check for bent push rods...

[jclary]

What about mechanically worn distributor weights/springs, etc.? If the distributor has been neglected, poor lubrication, etc., and sloppy worn components are dancing around, no amount of fine tuning the gap on the points, plugs, or adjusting the carburetor, will compensate.