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Old 01-06-2008, 11:13 AM   #1
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Default Spun Main Bearing?

So I have a 96 4.0L Ranger. I let my father use it for about a month while I was at school and now there is a loud knocking sound under the hood and I don't think it's even driveable. I haven't tried nor have I put a stethoscope up to it, which from reading other forums, is what I should do? However, what I'm trying to determine is whether or not my dad's prognosis could be viable. He believes that it is a spun main bearing. SO my question is, what does a spun main bearing sound like? And what does a busted rod sound like? This sound is pretty freaking loud, and there's chemical/burning smell upon disengage.

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Old 01-06-2008, 02:28 PM   #2
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Contact a oil analysis place, get a sample kit and send a sample back to them. Probably cost $20 - $30 dollars and they can tell what is worn by the metals and chemicals in the oil. Or you can get a mechanic .
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Old 01-06-2008, 07:43 PM   #3
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Well, one way to tell the difference between a broken rod and a spun main bearing is a cranking compression test. The broken rod will have zero compression....

But there are other possiblities, and an automotive stethoscope really is the right thing to do first. These are cheap.

Kona, how can oil analysis tell which bearings are thrashed? They are all made out of the same material.

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Old 01-06-2008, 08:03 PM   #4
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Drain your oil into a dish pan or some other clean pan. Shine a very bright light into the pan of oil and see if you see sparkles in the oil. Try blowing into the pan slightly and you should be able to tell something right away. If the oil looks like it has glittery material in it, youve wasted a bearing, or more. If youve broken a rod, the whole motor will be shaking like hell when you run it, and you will visibly see it shaking back and forth terribly. A broken rod will result in a massive imbalance in the rotating mass of the engine, thus casing the violent shaking. Hope this is some help......and that MAKG doesnt think im too far off. Im kidding of course.
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Old 01-06-2008, 09:38 PM   #5
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From my experience years ago, a busted rod sounds like an angry midget is inside your engine with a sledgehammer having a temper tantrum.

A spun bearing sounded like a rifle being discharged in full auto (I think what you guys call a Class 3) inside the crankcase.

Did that help? LOL
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