Join Date: May 2009
Location: North Carolina
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Rattling noise when running
Got the jeep running and most everything is going well, except...
When I first start it (i.e. cold start) there is a rattling noise that is RPM related. It almost sounds like a loose rocker arm hitting the valve cover (pulled the valve cover and no signs of that and retorqued the rocker studs bolts plush checked all push rods and no slop in those). After about a minute of running or so (plus some revving) the sounds gets noticeably quieter and will disappear when the clutch is pushed in. Let the clutch out fully and the noise is back (although quieter than when cold).
I need to try one more time, but I believe that on a cold start the clutch position did not affect the noise.
The guy that did the exhaust said he thought piston slap. However, this noise is a new development (since exhaust) and prior to that although it wasn't run much, I know it wasn't making this same sound. I'm still firmly in the break-in period on a rebuild (.030 over with new pistons, bearings, cam, 4.0L head). I don't think that piston slap would be a developed issue (if due to undersized pistons).
The only thing I can think of now is a bad throw-out bearing, but I wouldn't think engine temp would have an effect on that (making it go from uncomfortably loud rattling/knocking to just a minor annoyance). If anyone has had one that acted like that, please let me know. It doesn't make sense to me, but could be. It also idles smoothly, no apparent missing and the rattle appears to be coming from near the firewall (not sure top/bottom or bellhousing/engine).
P.S. Thanks for the starting help, ended up being an incorrect gasket between metering block and airhorn.