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1996 XJ Timing Chain

H

Hoss79

NAXJA Forum User
Location
Illinois NOT Chicago
Greetings, all! What sort of sound does a Jeep engine make when the timing chain breaks? I was a half mile from home, started my '96/360kmiles XJ, and engine sounded like ballbearings in a meatgrinder (transmission not in gear at the time). Shut engine off, turned on, same. Third re-start, limped it home, engine jiggling...last 50 yards were smooth.

I'm hoping it's NOT the timing chain, but if it is...Does any of this sound familiar? I haven't restarted it, not knowing if there was valve damage. I plan to pull plugs tonight/tomorrow, fingers crossed it's just a couple of damaged plugs.
 
If the timing chain went, it would simply stop running, after the sound of crunching and impending doom of course.
 
A broken timing chain should not damage the valves as the 4.0 is a non-interference engine.

If the timing chain did break, the engine would not run at all.

Is the check engine light on? If so, get a code reader and start there.

As far as the noise you heard, could be a number of things.

I would start with an oil change to see if there is anything floating around in the oil.

Then perhaps check the flex plate to see if you lost any of the bolts. It's probably not, judging by the "engine jiggling", but it's a quick and easy way to eliminate that potential problem.

Pull the plugs and check them.

IF you feel safe to do so, check the compression since the plugs are out.

It is possible the chain stretched enough to skip a tooth. That could make some noise and will cause the engine to run horribly.

Could be a broken connecting rod, broken piston, broken cam shaft, stuck lifter, etc, etc.....
 
Check your key codes. Mine has done much the same a few times for various reasons. Once it was an O2 sensor. The other times a Crank position sensor/sync sensor issue.

Sounds like it is bad enough to get a key code.

Might be something mechanical, but serous sensor issues can also sound really bad.
 
Sounds like a busted rod. Pull the plugs and do a compression test.
 
No Check Engine light. Might be burned out, though, it was on for a few years.

I had the angle sensor changed about 9 years ago, due to a different reason.

All of the breakage options...why would it suddenly run smooth again? Hoping for a plug misfire. It's injected, could be an injector issue. I'll tinker on it tonight, see if anything jumps out at me. Suggestions as to what to look for help!
 
Original_MudButt said:
I would start with an oil change to see if there is anything floating around in the oil.

Then perhaps check the flex plate to see if you lost any of the bolts. It's probably not, judging by the "engine jiggling", but it's a quick and easy way to eliminate that potential problem.

Pull the plugs and check them.

IF you feel safe to do so, check the compression since the plugs are out.

It is possible the chain stretched enough to skip a tooth. That could make some noise and will cause the engine to run horribly.

Could be a broken connecting rod, broken piston, broken cam shaft, stuck lifter, etc, etc.....
Click to expand...

old_man said:
Sounds like a busted rod. Pull the plugs and do a compression test.
Click to expand...

These are good ideas. In my experience electrical sensor or misfiring for other reasons does not cause a marbles in the crankcase type of sound. Has the Jeep had any knocking or other issues prior to this event?
 
When the rod first breaks, the free end swings wildly and hits the block. Soon afterwards, the swinging end of the rod gets broken off and falls in the pan. The motor runs smoother, but has a miss and somewhat lower power.

Either way, that much noise means something came apart. It's time to start looking.

Funny thing is, of all the 4.0L's I've seen throw a rod, it has always been cylinder #5.
 
No, no previous knocks or jiggles of any sort (outside of death wobble, and that's been sorta fixed).

So out of 6 valves, one rod could be busted...If the last stroke (or last several) slammed the valve all the way up, the smooth ending to the short drive could be attributed to the 5 remaining ones working as designed?

Never having dealt with the valves in an engine...Is it a complete pull and dismantle, or can it/they be changed with the engine in place?
 
For a valve to have come loose and banged around in the combustion chamber, then quieted down, it would have had to of busted through the top of the piston. A busted rod is totally different from a broken valve.

Either way, a quick compression check will tell you more than just about anything else. Both a busted rod and a bad valve will both show up. Either one of those pretty much makes the motor scrap.
 
The timing chain in my 96 stroker slowly and quietly ate itself over a few 10Kmi and when it finally went, it was like the typical crank, no-start scenario. Thank Jeep it's a non-interference engine.
 
Last edited:
Pulled plugs-no smashed ends, all evenly worn. Drained oil (dropping pan tonight)-all clean, nothing stuck to magnetic plug end. I had to turn jeep on to back it into the usual oil change position...all smooth.
 
Ran out of daylight, then had other evening business yesterday...I'm down to 3 remaining bolts. I'd like to smack whomever's bright idea it was to put hose looms to the connecting bolts, jeez. Gasket needs changing, anyway. I figured since we're in agreement it was NOT the chain, I would forgo the frontal disassemble.
 
If you take the cap off the distributor and take a note of the rotor position, bump the starter and the rotor has moved, then your timing chain hasn't broken.
 
gradon said:
If you take the cap off the distributor and take a note of the rotor position, bump the starter and the rotor has moved, then your timing chain hasn't broken.
Click to expand...

Friend of mine suggested corrosion on the thingy inside...as soon as the pan is back on, that's what I'll look at (providing nothing is in the pan). I'm easily distracted, :scared:
 
Hoss79 said:
Pulled plugs-no smashed ends, all evenly worn. Drained oil (dropping pan tonight)-all clean, nothing stuck to magnetic plug end. I had to turn jeep on to back it into the usual oil change position...all smooth.
Click to expand...

Just to let you know, the piston can't get high enough in the bore to hit the plugs.

Sounds like pulling the pan is a wise idea. Hopefully all is well.
 
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