Topic: Rattling noise when cold.

[shovelhead]

My 1997 Jeep TJ, automatic makes a terrible rattle when it's cold.  Many times after sitting for an extended period of time the engine is initially quiet, then after about 20 seconds it starts to make this rattling noise.  The noise is almost completely gone once the engine warms up.  Oil pressure when cold is about 50 lbs, hot about 25 lbs at idle.  I've tried using a mechanics stethoscope to isolate the source of the rattle to no avail.  I removed the dust cover off the transmission and checked the bolts to the torque converter, and they are tight.  I removed the belt, and ran the engine beltless, and the noise is the same.  I unplugged the spark plug wires, one at a time, with no change in noise.  All the spark plugs are perfectly light golden brown in color.  I suspect that I have a cracked flex plate in the center where I can't see it.  I posed a video on YouTube here.  Opinions?

http://youtu.be/DO0aXJh46_w

[sharpxmen]

imo piston skirt or connecting rod bearing in that order. Hard to make out from the sound in the video though, could also be a stuck lifter
it's fairly loud to be honest and it doesn't sound like a lifter but it could be the way the camera captures the sound.

[shovelhead]

Would a piston skirt or connecting rod bearing get quieter, almost gone, when the engine is warmed up?  And would the sound change if the related spark plug wire was pulled?
 

[shovelhead]

I think I'll pull the valve cover and see if there's anything obvious there.  I have a reputable transmission shop who said they can tell me by the sound whether it's a flex plate or not, I just have to get it down there.  I did find another video on YouTube of a Cherokee with a cracked flex plate that sounds very similar.
http://youtu.be/Ros1znVrcgs

[aw12345]

Would a piston skirt or connecting rod bearing get quieter, almost gone, when the engine is warmed up?  And would the sound change if the related spark plug wire was pulled?
 

Piston slap would quiet down some when warmed up, sound should change when you pull a spark plug wire. Flexplate generally the sound would change some when you put it in gear, does it?

[shovelhead]

It does get a little louder when in gear, and under load.

[grumpygy]

It does get a little louder when in gear, and under load.

My 2000 GMC Sierra 1500 Has that very same noise.  When  Cold it is loud, drop it in gear and its really loud.  Been going one for about 4 years.  When warm it is so quite I have almost tried to restart it a couple of times.  The way I drive if it was going to come apart it would have a while ago.


  But its piston slap, that year truck is known for that, the skirt is too short.   So to me if it was that there would be others with this noise or your engine has been rebuilt at some time.

[grumpygy]

Have one other after looking at the TSB's.  Are all your exhaust bolts there.  Seems the outer ones are breaking off.

[sharpxmen]

just from your video it sounds louder under hood than under the Jeep, not sure if that means anything for the flex plate or not, if it wasn't going away i would have also thought of a stuck valve maybe, but since it quiets down when warm that doesn't seem to be it. Lifter or piston slap is still my best guess. For the flex plate, common sense tells me it shouldn't go away with engine temp, but who knows. Looking forward to hear what's the culprit once you have it figured out.

[shovelhead]

I recently replaced the exhaust manifold, it had three major cracks, and all the bolts were OK.  When I started it this morning, it was perfectly quiet for about 20 seconds, then the rattling noise gradually started.  After a few minutes of driving, it quiets down again significantly.

[Jeffy]

I would check for exhaust leaks.

[grumpygy]

Here is something to try.

NOTE: Cold engine piston slap that ceases after a few minutes operating time is normal on 1980-81 Jeep 4 cylinder engines.

(1) If noise is not sensitive to engine load, clean engine piston tops and combustion chambers with AMC combustion chamber cleaner or equivalent.

(2) If noise ceases after using combustion chamber cleaner, return automobile to owner.

(3) If noise does not cease, check piston-to-cylinder wall clearance. if clearance is excessive, pistons may be knurled to provide desired clearance. However, if knurling service is not readily available, 0.005 oversize piston and ring sets may be installed to obtain desired clearance.

NOTE: Piston-to-wall clearance should be 0.0027 - 0.0033 (0.0635 - 0.0838mm). Measure piston diameter at the pin centerline 1-3/16 below the piston pin (on the piston skirt). Measure the cylinder bore at a point 2-1/4 below the top of the bore. Cylinder taper should be no more than 0.001 (0.0508mm).

  But has the noise been there before you changed the Exh Manifold gasket.  Mine also had a noise and it was a broken bolt/Stud. 

[sharpxmen]

that's a totally different motor, not normal for the 2.5L or 4.0L TJ (same pistons).

[grumpygy]

that's a totally different motor, not normal for the 2.5L or 4.0L TJ (same pistons).

Actually the piston Slap was listed for a tj when I did find it..  I was just showing the above as a way to check for piston slap.

[shovelhead]

For some reason, I started it up today, and something strange happened.  It started, then coughed and died just after starting.  I restarted it, and now the rattling noise is almost completely gone.  It runs and idles fine, and there's just a faint tick, like a lifter.