So I bought the car not too long ago, with a blown head gasket. Owner neglected the piss out of it. He used water for coolant because it burned so much, took out the thermostat, and used low grade gas at all times. When I pulled the motor out I found the head gaskets were blown visibly in 5 different places. I sent all the parts to the machine shop (including the block halves) and had them inspect. They recommended a full re-ring. Had everything decked straight, cylinders ball honed, pistons inspected and cleaned up, and a compete head job. They said the main bearings and crank looked ok, as did the pistons for a budget rebuild. Rod bearings were replaced for piece of mind. New rings fitted and installed.
Fast forward about 600 miles since rebuild. The engine vibrates substantially in drive. Feels like all the motor mounts are broken, but they're not. No misfires etc. in park or N the vibration is gone. However, there is also a "knocking" noise. Now, this appears ONLY after the engine is fully up to temp, only in P or N, and only at idle. No driveability issues and the noise is gone above 1000rpms. It is very noticeable and slow paced like rod knock, but almost sounds too "tingy" for a connecting rod. Like something hitting against the trans bell housing "ting ting ting". Whereas the 2005 LGT that I had that tossed a rod, had a very distinct "clock clock clock" noise.
I'm wondering I something is misaligned or somehow out of balance, causing the vibration and noise? Maybe a cracked flex plate? Any ideas appreciated, I'll be inspecting further tonight.