Critic; On a tangent, I also had dealership problems. My 1980 Dodge Omni was diagnosed with an ignition computer problem. Before the repair shop sent it to the nearby dealer, they specifically asked if they had a replacement in stock, and they (supposedly) did. The dealership replaced the Hall Effect sensor and said it was fixed. I went to pick it up, and of course it wouldn't start. I had to drive across town in a borrowed car on a rainy Friday night to get a computer from another dealer to fix the car. I did get some consolation that the mechanic that did the repair was checking the ignition, standing in a puddle. When the engine stopped cranking, the ignition fired and 'lit him up'. And the shop manager went up one side of the dealership service manager and down the other for taking the job without having the computer. I also was told that a couple of other customers that had been referred to the dealership for a failed ignition computer returned to say the computer was not the problem, some other repair had been done. At which point the shop manager pointed to the shiny new ignition computer under the hood. Dealerships don't make profits from warranty ignition computer replacements, but they do from other work.
Yes, I remember that notion in the 1970s, Ratski, where you were supposed to avoid cars that were produced on Monday or Friday. Not usre how you swere supposed to determine that. I also remember the very real sabotage that occurred when workers were unhappy.
My dad told me a story years ago about a guy that bought a new olds but it seemed to be burning a lot of oil. Turned out some of the piston rings were never installed. That one must have been assembled on a Monday or Friday.
I'm not familiar with that particular motor, but since you've apparently ruled out the damper and flexplate, I can't think of anything in crank, rods or pistons that could cause a gradual increase in vibration over a period of several months.
Cranks are typically balanced by drilling holes in the counterweights, and I doubt there are any counterweight eating bacteria around, so that's out.
Rods are either pressure cast from powdered metal (pre-balanced) or forged and ground on the ends for balance. Nothing I can foresee would gradually change the weight of any of the rods. Unless the aforementioned bacteria developed a propensity for munching on con rods.
Pistons are one piece, and unless the rings are slowly disintegrating, I can't see them gradually changing weight either. If they were coming apart, you would hear it or lose power.
I think you would have noticed any loose con rod or main cap bolts when you tore it down.
If a bearing or wrist pin was going away, you would have heard it.
The only thing left that I can think of would be a bent crank, but that seems even more unlikely than the bacteria solution.
Is this an even-fire V6 with offset crank pins, or an odd-fire with straight crank pins? I have seen offset journal cranks crack in the area between the two offset bearing surfaces, but it's extremely rare, and usually causes a lot more problems than just some vibration. And I think you would have noticed if the crank came out in two pieces.
If the problem was with the crank, rods or pistons, you've got me on this one.
My first move in diagnosis would have been to drop all the belts off the motor, and fire it up to see if anything had changed.
I then would stick it on a scope and see if the firing pulses were showing up at the right times.
Assuming that nothing was found, and assuming the engine was running normally, inspection of the flexplate and converter would probably be next on my list. If I suspected the convertor for some reason, I would unbolt it from the flywheel, push it back out of the way and fire the motor again.
Assuming it was still vibrating, I would re-inspect each balance weight location on the flywheel to make sure it was still there.
After that, I would probably try a new balancer before tearing into things any further.
The next step would necessitate tearing down the motor, but with 180K on it, it's probably time for a new one anyway, and it's rarely economical for a dealer to rebuild an old motor, as rebuild shops can do it faster and usually much cheaper.
You might be able to rebuild it cheaper yourself, but only if you value your time at zero $/hr. and aren't impressed with the concept of warranties.
New rings, pistons, bearings, gaskets, seals, grind the crank, grind/replace the valves/seats, bore and deck the block, reface the heads, new valve springs, new injectors, new cams, new timing chain & gears, new oil & water pumps, etc. etc.
Add up all the parts and machining costs, add some $ for your own time, and methinks a rebuilt motor (with a warranty) is probably a better bet.
But I'm still very curious as to what the problem was. Other than it being a Ford, that is...
xti: the motor was running fine, except for the vibration. It was not misfiring. There were no strange noises. Oil pressure and coolant temperature were normal. There was no loss of power. The vibration developed over a period of 3 - 4 months.
I did not check the ignition timing because it is a "distributorless" ignition system, and there is no timing adjustment.
Sometimes flexplates or torque converters have welded on balancing weights that can come off, but that would give you a sudden, rather than a gradual increase in vibration - besides, they replaced them with no improvement.
A quick inspection of these parts usually shows spot weld marks surrounded by nice clean metal that indicates the former presence of such welded weights.
My guess as to a gradual increase would be that the outer ring of the balancer had come loose from the rubber liner and was rotating relative to the crank.
If this is an internally balanced motor, not much would happen if this occurred, however if it is an externally balanced motor, all hell would break loose as it rotated.
The outer ring of these balancers typically have an intentional out-of-balance condition built into them to counteract the natural out-of-balance condition of the motor. There would most likely also be weights welded to the flexplate.
That is about the only way I could think of that would cause a gradual increase in vibration.
Oil on balancer + 180,000 miles = deteriorated rubber. The hint would be the broken motor mounts - that rubber came apart as well. The vibration of the motor probably helped kill the mounts and the balancer even faster than normal.
Another possiblity is that the damper turned relative to the crank due to a sheared key. Some engines don't even have a keyway anymore, although that's pretty unlikely with an externally balanced motor.
I have a 2000 Mustang with 3.8-liter V6 engine and automatic transmission that had about 180,000 miles when it gradually developed a severe vibration. The vibration could be felt with the car parked or while driving, but it was worst at about 1,200 RPM.
I was being sent out of town on a long business trip when I decided to take the car to a Ford dealership to have the vibration diagnosed. I called several local Ford dealers, trying to find one that had a vibration analyzer. In the hands of a trained and experienced technician, a good vibration analyzer can help determine the approximate location of the vibration, and in some cases pinpoint the cause of the vibration.
I dropped the car off at the dealer, and after a couple of days, they called and said that they wanted to replace the engine mounts, which were a little cracked. I knew that the mounts were not the cause of the vibration, but I let the dealer replace them to the tune of $450, so they would proceed with the vibration diagnosis.
I soon found out that the service manager had lied about having a vibration analyzer. They disassembled the front of the engine to inspect the balance shaft and its drive chain. They also replaced the torque converter and flex plate. They were kind enough to only charge me labor for the remainder of the diagnosis, returning the old torque converter and flex plate to the car after they discovered that these were not the cause of the vibration. After they burned through another $400 in labor, they gave me their diagnosis of the problem: they had isolated the vibration to the engine. Their solution was to replace the engine with a rebuilt one, which I thought was not necessary, so when I returned from my business trip, I drove the car home.
I removed the engine from the car, removed the rotating assembly (crankshaft, rods, pistons, flexplate, and harmonic damper) from the engine, and took it to a machine shop to have its balance checked. The machine shop quickly found the cause of the vibration.
Would you care to guess the cause of the vibration, or offer what would have been your proposed diagnostic plan? Did I really have to disassemble the engine?
Focus on Fundamentals consists of 45-minute on-line classes that cover a host of technologies. You learn without leaving the comfort of your desk. All classes are taught by subject-matter experts and all are archived. So if you can't attend live, attend at your convenience.