GMC Repair: loss of oil pressure, oil pressure gauge, shaft assembly

Question
QUESTION: My 1999 gmc sle jimmy all a sudden all @ once had check gauges light which followed by zero oil pressure. If I press slightly on accelerator the oil pressure gauge goes up but does not stay there. If its cold or running less than 10 miles its ok but run it longer n it drips. There is a little lower rattle on acceleration only if hard acceleration. No colored smoke. I assume crank shaft assembly to change out oil pump, timing chain, bearings etc... Am I correct? If so, how much could I expect this to cost me?

ANSWER: You are correct. You do not need to change the timing chain or crank bearing, but may as well since it is dropped and out of the vehicle. Ask the mechanic to check condition and wear. Ninety percent of the time labor will be your biggest expense. I would say you are looking at about five hundred. You may be able to tackle some of this yourself.

 All you really need is a manual from the auto parts retailer and a basic set of hand tools in most cases. Just make sure to place the rod ends and bolts out exactly how they came off.

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QUESTION: Jimmy is still in my basement for the garage said $1200 or more to drop engine to get @ oil pump and they said lower bearings needs changed and the crank shaft assembly includes all the extras like timing chain n such. I've been out of work n have limited income and am afraid they are taking advantage f me for I'm a woman? It just seems weird that all of these major parts went bad so quick and no warning. I take very good care of my jimmy. Garage kept only 10000 miles a year and oil change regularly. Is it possible for all the oil n bearings to go bad with no warning? As soon as lite came on to check gauges I took to garage and it seemed to have gone downhill since. I didn't notice any rattling anytime b4 the gauge lite came on to check gauge. When it did I went directly to garage and now all this? Is it possible to occur this way?

Answer
For arguement sake, we will say you have 50,000 miles on your Jimmy. when you get into the lower part of the engine, many things can happen here. I am assuming you have a V6 in your Jimmy. You cannot replace one crank bearing. The reason for this is that if you only replace one, you have the other crank bearings that still have the 50K miles on the other bearings. These bearing are actually metal or brass sleeves in the shape of a half circle. The tolerances/clearances from the bearing to the crank are thousandths of an inch. This is extremely critical. If your mechanic does not get this part right, any mechanic for that matter, it will cause you to spend more time and money overhauling your motor.

 This also applies to connecting rods (connects piston to crank). These also have bearings/sleeves in the same manner as the crank. This applies to lifters, rods, injectors, etc. When you have more than one of a part, you replace them all. IE: spark plugs/wires.

 Your mechanic is not ripping you off. You do have to pull the oil pan to get to the oil pump. No mechanic I know looks forward to this daunting task. To answer your question, yes this could happen without any warning.