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99 Jeep Wrangler 4.0L engine rapping


Tomcat0403
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For those of you who have a jeep or any mechanical knowledge I need some input. My jeeps engine has developed a very loud rapping noise, coming directly from the engine block. I have had lifter noise for the past few years but this is very different. It sounds like a midget is using a small hammer and hitting the engine, and it varies directly with the rpm whether in or out of gear. Oil level is good, recently changed (1500 miles since), oil pressure is good, drives normal, no loss of power, no sputtering, no smoke, no check engine light. The only thing that has been leaking is the gasket around the water pump due to a broken bolt. Very slow leak and I keep it in check and has not overheated since the fan clutch/waterpump took a shit last year.

I have checked the forums for the most part and haven't really found anything which is really surprising.

Any help would be appreciated.

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Very expensive. Once it starts knocking, it usually ruins the crankshaft, and egg shapes the connecting rod. Engine basically need to come apart, crankshaft reground, or replaced, and the bad rod replaced. The engine should be completely disassembled and cleaned, because you now have metal shavings all through it. The oil pump should be replaced as insurance while it's open. You might be better off finding a lower mile used one, or a remanufactured engine.

The other possibility would be a broken piston skirt, which would be pretty close to the same deal, nut would probably mean that the engine block is trashed.

Sorry, but it doesn't sound like a good thing. :(

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Very expensive. Once it starts knocking, it usually ruins the crankshaft, and egg shapes the connecting rod. Engine basically need to come apart, crankshaft reground, or replaced, and the bad rod replaced. The engine should be completely disassembled and cleaned, because you now have metal shavings all through it. The oil pump should be replaced as insurance while it's open. You might be better off finding a lower mile used one, or a remanufactured engine.

The other possibility would be a broken piston skirt, which would be pretty close to the same deal, nut would probably mean that the engine block is trashed.

Sorry, but it doesn't sound like a good thing. :(

This is it here. Sometimes its cheaper to replace whole motor. I wouldn't drive it any more. You run the the risk of the rod coming off completely and it going through the engine block. In any case a new motor would be the cure. Or post it for sale on CL as custom.

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I have to agree with Grapesmuggler and jporter: Bottom end bearing- continuing to running the engine can cause total failure of drivetrain if you are moving and engine locks up - can also wipe out whole engine beyond possibility of rebuild, transmission, u-joints and possibly rear end (that is what happened to me at 55 mph). That is a common engine also used in the Cherokees and Grand Cherokees. Good Luck

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If they have them - Complete engine from Pick-N-Pull down on Groveport Rd. will usually be under $400 with a 30 day warranty (unless they changed warranty recently) Look for a stock suspension cherokee or grand cherokee that was T-Boned - hit in the side (odds are that it was running/being driven when wrecked) Note: the Cherokees are usually urban vehicles that see mild use as opposed to wranglers the get more offroad time.

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I have to agree with Grapesmuggler and jporter: Bottom end bearing- continuing to running the engine can cause total failure of drivetrain if you are moving and engine locks up - can also wipe out whole engine beyond possibility of rebuild, transmission, u-joints and possibly rear end (that is what happened to me at 55 mph). That is a common engine also used in the Cherokees and Grand Cherokees. Good Luck

Also, if it becomes a catastrophic failure (rod through the side of the block) a reman company probably won't give you credit for the core.

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If they have them - Complete engine from Pick-N-Pull down on Groveport Rd. will usually be under $400 with a 30 day warranty (unless they changed warranty recently) Look for a stock suspension cherokee or grand cherokee that was T-Boned - hit in the side (odds are that it was running/being driven when wrecked) Note: the Cherokees are usually urban vehicles that see mild use as opposed to wranglers the get more offroad time.

$400!?!?!? They used to be $99!!!

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Can you pull the oil pan and check the bearings?

Last time I heard this is was a spun bearing, confirmed by pulling the oil pan and feeling the slop on the rod. Pulled the end cap and found the bearing was smooshed down to paper-thin. Used engine was 400.

Edited by Scruit
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