Well now, got the compression numbers on the vr6 passat that gave up the ghost a couple of weeks ago. Cyls 2,4 and 6 are all around 180 psi (cold engine). Cyls 1,3 and 5, O psi, 60 psi, and 0 psi. >
> Bent valves on 3 and 5? Skipped tooth on timing chain? blown timing chain tensioner? All of the above? Any bets before I take off the valve cover? >
And JRE responded
Sounds like a cam stopped. Ugly if it's an interference engine. A >couple other possible causes: Sheared woodruff key or broken (or >backed-out) dowel on cam sprocket, broken camshaft (esp. if engine ran >low on oil).
And JRE takes the prize on this one. Finally got around to pulling the valve cover and sprocket cover. Rear sprocket had come completely undone and the dowel had backed out to the sprocket cover, and the woodruff key had sheared. The thing was wobbling all over the place. I'm amazed that I got any compression at all on cyl 3.
The thing I'm wondering is how this happened in the first place. Since I've had the monster (2 years) it's been really well-cared for. Plenty of oil and coolant...etc. One weird thing - I found broken pieces of a timing chain tensioner inside the upper sprocket cover, but the tenisoners themselves appear fine. I wonder if maybe somebody replaced the tensioners at some point and rebuilt the head, but didn't torque the sprocket properly...? Freaky.
Anyway, next weekend I get to see how bad the valves look.