96 Saturn engine knocking

It could be just about anything. What is the quality record of the engine rebuilder that you used? What warranty did they provide to you?

You really need to isolate the source of the noise using a stethoscope to determine its cause. Could it be an exhaust manifold leak or something else non-internal to the re-built engine?

Bob

Knocking that stops under load is exactly what happened to me - and it was a rod bearing that had spun. Here's what it sounded like at idle:

A tip - don't drive it that way and fix it as soon as possible, or the bits of the bearing that wear away will circulate and cause more damage.

Lane [ lane (at) evilplastic.com ]

Internal noises that sound like lower end problems MUST be diagnosed ASAP to prevent further catastrophic damage. When a crankshaft bearing fails it usually takes a lot with it. DO NOT DRIVE THIS CAR.

Read what the others have said here. Put the car on some planks to give yourself some clearance to work under front. Chock the wheels, you will be doing a lot of running in neutral and your parking brake can fail. Check the easy stuff first, engine and accessory and exhaust mounts. Install a real oil pressure test gauge, position it so you can read it as you start the motor. Make a test log to record some after start tests. Have a real good listen to the motor, try to determine the source location of any noises, if you have knowledgeable friends get their help to listen. Piston and crank failures have pretty distinct sounds, they are usually very sharp and vary substantially when engine speed changes. They even sound expensive. Write down the results of following tests.

Start engine and run @ idle, observe when the oil idiot light goes out and how long it takes for the engine oil pressure to build and what is max @ idle & 1000 & 1500 @ 2000 rpm

Blip the throttle and listen for internal noise with a mechanics diaphragm probe stethoscope (a piece of hose works but is harder to interpret). Listen particularly for sounds on rapidly closing the throttle, this is when the con rod bearings are unloaded and can float loosely, pistons are also free to slap and these sounds are often difficult to distinguish. Record what the oil pressure does as you vary the engine speed and how fast it drops to idle pressure. (rapid pressure drop can indicate excessive bearing clearance)

Examine the plugs and do a compression check.

Have a look inside the valve cover, failed valve train can make strange noises into the manifolds, drop in power is not always large. Use some plastic to catch the oil spray and have a look while the engine is running, use your hose to listen to each valve tip.

Drain the oil into a clean container. Allow to settle and check for coolant as you strain the oil through a cloth, check with a magnet and for other particles of metal or other.

Cut apart the oil filter (use a pipe cutter or a cold chisel, do not use a saw or grinder) and wash the paper in a clean can of solvent. Examine the filter with a magnifying glass. Run the solvent though a coffee filter and check for particles.

Review your results and make sure you have not overlooked something easy.

Remove the oil pan (you may need to raise the motor?) and check the crank assembly and piston undersides, rotate the crank and inspect piston skirts and cylinder bores with a strong light.. Check for loose bolts. Remove bearing caps to check bearing wear surface and crankshaft for smoothness and color. Check bearing clearances with plastigage.

Faulty assembly is always suspect in crank failures. Were the con rod bolts removed? Did YOU check the bearing clearances at assembly? How? Did you torque the bolts dry? or with Loctite? Did you add a litle for mother? Faulty machining many be the cause of the failure but the assembler usually carries the can, consider yourself lucky if a failed bearing does not damage the crank.

Just my .02, Good luck

At the suggestion of a friend, I ran another compression test - it's within spec. I also checked the plugs - couldn't be burning better. Now for the bad news. I listened carefully while it was idling. It seemed to be coming from the head directly above the number one cylinder. I took the valve cover gasket off just to take a look. Start with the easy stuff, I thought. At first I couldn't see anything wrong, but then I noticed one of the bolts holding the timing chain guide was broken. Coincidently, these bolts hold the first cam shaft bearing cap on. When I tried to remove the other bolt, it broke as soon as I put a wrench on it. Must of been cracked.

Any suggestions for removing broken bolts from an aluminum head? I drilled one and tried to use a bolt extractor. It won't even budge. I'm afraid I'm going to twist off the extractor. Should I just get a new or rebuilt head? Maybe reuse the cam shafts? Any suggestions are welcome.

The best way I know of to remove broken bolts is to weld a washer on to the broken bolt. Allow to cool, clean weld, then weld a large nut (or a bolt) onto the washer. Allow to cool before using a wrench to turn out the (now hopefully shrunken) broken bolt. Some prefer a wire feed welder for this job.

Works better than ANY extractor I have ever tried and eliminates the (good) chance that you will drill off center or break the drill or extractor which are hardened and brittle. Works good on hardened bolts and sometimes on broken drills and extractors.

I have had some success with (larger) bolts broken below the surface by fitting a small piece of steel pipe to the broken bolt and then raising the heat and sticking the rod down inside the pipe and welding by sound. Usually takes multiple tries. Caution, do not burn through the side of the pipe.

YMMV