Spun Main Bearing?

cwcnoles03 · 01-06-2008, 10:13 AM

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.

Thanks

Kona · 01-06-2008, 01:28 PM

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 .

**MAKG** · 01-06-2008, 06:43 PM

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.

fordwheelinman · 01-06-2008, 07:03 PM

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.

Silverado · 01-06-2008, 08:38 PM

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

01-06-2008, 10:13 AM	#1
cwcnoles03 New Member Join Date: Jan 2008 Year: 1996 Make: Ford Model: Ranger EXT Posts: 7 Rep Power: 0 iTrader: (0)	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. Thanks
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01-06-2008, 01:28 PM	#2
Kona Member Join Date: Nov 2007 Location: Interior of British Columbia Year: 1991 Make: Ford Model: Ranger Super Cab Engine: 4.0L Class: 4X4 Used For: everything Posts: 546 Rep Power: 13 iTrader: (0)	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 . __________________ 91 Ranger XLT SCab 4.0L 5 Spd,4.56 gears, Spartan locker ,Skyjacker 6" w Skyjacker radius arms, Deaver G50 r springs, Belltech shackles, Flowmaster 40,Winch, 33's of some sort
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01-06-2008, 06:43 PM	#3
MAKG RBV Technical Advisor Join Date: Aug 2007 Location: California central coast Year: 1991 Make: Ford Model: Explorer Engine: 4.0L Class: 4x4 Posts: 4,643 Rep Power: 21 iTrader: (0)	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. __________________ 1990 VW Jetta GL, 1.8L 8V gasoline engine, manual transmission, painted in oxidized red paint and ponderosa pine sap, unknown mileage. 1991 Exploder, 4.0L, M5OD-R1 manual transmission, electronic BW1354 transfer case, 3.54 gears, 31 inch tires, icky two-tone blue paint with little clear coat, 230K miles. 1972 Chevy C-10, 250 I-6, SM465 (2WD) four-on-the-floor, 3.73 gears in a GM 12-bolt, puke green with a white cab. The "4 wheeled trash can," with x70K miles. x is probably 2.
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01-06-2008, 07:03 PM	#4
fordwheelinman Member Join Date: Aug 2007 Year: 1994 Make: Ford Model: Explorer 4 door Engine: 4.0L Class: 4x4 Used For: DD Posts: 477 Rep Power: 12 iTrader: (2)	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. __________________ 1994 Explorer 4 door- 4L ohv, FACTORY M5OD, working electric 4x4, new DD, awaiting 31x10.50's on black stock wheels 1978 F150- 4x4, 400 V8, C6, 31x10.50x15 adventuro all terrains on stock steels-towing, 33x12.50x15 BFG All terrain on mag 15x8.5, custom in bed gooseneck, waiting on custom flatbed *1989 Bronco II-Converted 4x2 to 4x4 with 2.9 bored .060, ported/polished heads, port matched manifolds, a4ld, man 1350, D28/7.5 4.10's in both L/S in rear: waiting on motor
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01-06-2008, 08:38 PM	#5
Silverado Junior Member Join Date: Dec 2007 Location: Fort McMurray, AB Canada Year: 1998 Make: Ford Model: Ranger XLT Posts: 68 Rep Power: 11 iTrader: (0)	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 __________________ 98 Ranger XLT Regular Cab Flareside 3.0 4X4 310,000KM pain in my ass!
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