Posted by Paul on October 08, 2003 at 18:05:42:
After replacing blown head gasket on my "late model" Atomic 4 and running motor around 4-5 hours with no problems, now I'm getting a nasty metal-on-metal thunk type noise at random intervals. The noise appears unrelated to engine speed and if I'm in neutral or forward. Oil pressure and temp are good and the engine doesn't hesitate when noise occurs. I did (with difficulty) remove the side cooling jacket cover and remove significant amount of crud from cooling system (also had transmission cover off) during head gasket replacement so I thought maybe I lost a socket, bolt, etc. in there somehow. Ran a magnet through bottom of engine through transmission cover - no metal fragments, shavings, etc. My initial thought was spun bearing but seems like spun bearing noise would be more constant and load dependent. Neighbor thinks maybe sticking valve so ran "motor flush" for 5 minutes, drained everything and ran with oil/Marvel Mystery Oil combination - no help. Noise just comes and goes but sounds very nasty like something's getting ready to let go. Motor starts and runs fine except for noise.
Anybody experienced anything like this or have any ideas?