6.2 "Death Shake"?

[BobND]

I'm working on a 1984 K-10 6.2, 700R4 . There is an odd vibration at idle. Damper appears good and does not wobble. Counterweight is present on flexplate, which does not appear to be cracked.

Compression is pretty close to 380 across the board.

Exhaust port temperature is very close on all cylinders, measured with an infra-red heat gun.

Loosening the injector lines one at a time does not seem to indentify a definitive weak cylinder.

Besides the shake at idle, it has an unbearable shake the instant the TC locks.

Somewhat coincidentally with the shake, it developed a rear main seal leak (gush).

I seem to recall some 6.2's developing a "death shake" when the main webs and/or the crankshaft cracked. Has anyone experienced this, or does anyone have any other thoughts?

[More Power]

Loose timing chain??

MP

[humding]

I don't like the sound of that. FYI when mine cracked the main webs it ran perfect on idle and the vibration started around 2250 RPM upwards. I initially thought it may be a loose flywheel or clutch so I pulled the gearbox. Everything was OK so I ran the engine without the box and everything sounded & felt perfect. I put the clutch back on the flywheel and repeated again and everything was fine. I then bolted back the box to the engine and again ran perfect. I was sure everything was Ok so put everything back and went for a test drive and the vibration showed up again. It was very bad on pressing he clutch as it was pushing on the centre bearing which was cracked the worse.

[BobND]

That's what I'm worried about. It will probably be a week before I can tear into it.