A friend of mine took his Chevy Impala into a local GM dealer for service, claiming it had a vibration in the engine at certain speeds. The dealer techs confirmed the vibration and also noticed that the oil pressure light intermittently flickered on and off, mostly during idling. This seemed to go away as the engine RPM increased.
The service crew installed a new oil pressure sender, but that didn’t solve the problem. They checked the oil pressure, and although it was very low at idling, it came up enough at higher RPMs to be adequate. The engine ran fine, so they decided to concentrate on the vibration, which only occurred at certain RPMs and didn't change much whether it was being driven or free revved in the shop.
After a week of fruitless attempts to get rid of it by changing the damper, the alternator, the water pump, the power steering pump, and even the flywheel and torque converter, they were no closer to figuring out the problem. They returned the car, with a promise to look at it again once they heard back from GM. A week later, the engine made a horrible racket and died abruptly in traffic. The owner had the car towed back to the dealer, where the service crew tore it down and discovered the reason for the oil light, the vibration, and the sudden demise of the motor.
The crankshaft was broken in half. During initial assembly, someone had forgotten to install the center lower main bearing shell. The cast crankshaft had been flexing up and down at that point until it finally failed.
This entry was submitted by Dave James and edited by Rob Spiegel.
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No, I don't always get the diagnoses correct the first time, but I know an accessory on the engine wouldn't cause erratic engine speed unless it was locking up completely of which is going to burn the belt up. A flat spot on the crank can cause engine vibration and even noise. Anyway, I think a mechanic would know right away if one of the accessories was having a problem by simply spinning the pully with the belt off and feeling for roughness. No doubt, it is a unique problem that you wouldn't expect a new engine to have and probably not the easiest problem to solve since your probably looking for a hair line crack somewhere on the crank.
GlennA, how can we tolerate such ignorance from the service person? If they fail or ignored in tightening the brake screw, what will happens to the passengers. Moreover, most of the service centers are offering one or two test drives at different levels, before delivering the vehicle. This can make sure that your vehicle is in perfect condition.
To OLD CURMUDGEON, you are correct about woulda, shoulda, etc. being moot. The real value of our discussions is that it adds to our knowledge base so that we hopefully don't repeat those earlier mistakes, But, (loud sigh here) human history is littered with repeated blunders, hence fallen bridges, burst dams, and yes, even a few wars.
I think that this happened so many decades ago that it doesn't matter what they SHOULD or SHOULD NOT have done. But, continuing this thread leads me to suggest that the proper plan of attack should have been to call a district CHEVROLET troubleshooter into the discussion, who maybe would have suggested a different plan for attacking the vibration problem, instead of wasting precious time, resources & parts on "maybe" fixes. All the auto companies maintain a cadre of highly qualified supervisory personnel to deal with the esoteric & arcane problems that arise with auto diagnosis.
On a personal note regarding this situation, I had an uncle who purchased a new Cadillac in the early 1960s. The vehicle never ran correctly from day one. With 472 cu. in. under the hood, it should have flown, but didn't. He brought it back to the dealer for service. They kept the vehicle for the better part of a week, testing everything they could think of. Then, they called a Cadillac troubleshooter, who inspected the vehicle. While it was on the lift, with the engine running & a mechanic in the driver's seat, this troubleshooter was under the vehicle observing the operation. As he passed by the rear of the vehicle, he noticed that the exhaust on one side was far more pronounced (volume of air. NOT sound), so he directed the mechanics to disassemble the entire exhaust system all the way to the exhaust manifolds. What did they find? Well, they found a 6 1/2 oz. green COKE bottle stuffed in one tailpipe near the inlet to the muffler. They removed it, reassembled the exhaust system, and delivered the vehicle to my uncle's estate. The family drove the car for several years WITHOUT a hint of a problem! The ONLY question remained, "was it a Monday car or a Friday car?"
Morphing back to the Heathkit, I recall many years ago, my boss said, "We need a two channel, precision DC-coupled scope for product development, so I bought a Heathkit, and you put it together!" At that time we were doing some pioneering work in solid-state alarm and telemetering systems and the 'scope would be handy. Anyway, I built the 'scope, and it worked OK, but ironically it had to be sent to a facility with a precision 'scope for calibration! Between the kit cost, my labor, and the calibration and shipping, we would have saved time and money with a commercial oscilloscope.
Morphing back to engine vibration, it seems the repair guys could have disconnected the external rotating components by unhooking the fan and accessory belts first. This would eliminate the alternator, water pump, smog pump (if equipped), power steer pump, and air conditioning compressor as a vibration source. That would leave the transmission and engine as a vibration source. Then, carefully block the engine, and unbolt the tranny, and run the engine. If vibration remained, it would then be isolated to the engine. If vibration went away, then the trans was the likely culprit. Watcha think?
To xti and OLD CURMUDGEON: Hmmm..... morphed into a Heathkit thread? True enough, but thanks to Design News we have this freewheeling exchange of ideas and subjects, and we've all had a chance to meet, albeit virtually. By the way, I haven't yet tried the suggestions; with our local (Chicago area) weather so nice, my wife somehow co-opted me into helping get our little garden ready for planting, etc. I did find some other Heathkit forums, and one suggested that an LM317 is a better substitute for the unobtainable Heath regulator chip.
John; When you are troubleshooting, do you replace the most difficult and most expensive part first ? I start with possible adjustments, working through the most likely and the most easily replaced parts. Only after the easy and cheap stuff didn't work, would I look at the difficult and expensive stuff. However, that does not mean changing parts for the sake of changing parts = the part must be related to the problem.
Even if one of the tech's was a paranormal, that does not mean that the missing support would have been readily visible with the oil pan off. Monday morning quarterbacking is always easier.
Wow! They replaced a waterpump, steering pump, alternator, and a whole bunch of other stuff before figuring this out? Man, sounds like they took your credit card for a ride. Hope all those replaced parts didn't cost you a cent. Sounds like an afternoon of poping the oil pan off and inspecting the crank and bearings would have solved the question of the day.
As far a crate engines goes, I'd say they have become popular because no body knows how to rebuild an engine and if they do, it's hard to find an engine machine shop.
When your lab is only one scope, one meter, and one homebrew function generator and power supply, the scope is stage center. But this one wasn't working right.
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