[Vwdiesel] Radically Slipped Timing

[Val Christian]

Sandy,

I had a similar but different "failure".  It happened on an 84 rabbit,
which had about 260Kmiles at the time.  I had the head off at 175Kmiles,
and it was serviced and replaced.  On that engine, there is no key
in the camshaft, although there is a keyway.  There's also a keyway
in the camshaft sprocket pulley.  There's a bolt which is torqued to
spec as the timing is set.  But no key.

So I'm tooling home on a hot Friday after work, exit the expressway,
and as I'm turning and downshifting (with the clutch in) I feel the engine
shudder to a hard stop.  I had the presence to not pop the clutch back
out for a restart.  Since the engine stopped so abruptly, it was not
likely that it was starved of fuel or some other reason.  I coasted
off the bridge over the expressway, and got the car off to the side.
I put it into 5th, and rocked the car back and forth, with the hood up.
Heard a clink and felt the stop in each direction.

Called the neighbor dairy farmer who brought a pickup and a tow rope.
Later that evening I had the head off, and saw one bent valve, and a
broken off valve which bounced against the valve seat and
dimpled the piston where the valve hit.  I had two valves installed, and
the others checked.  With a broken rat-tail file, I cleaned the burrs
off the piston.  Put everything back together and it ran fine.

If the sprocket pulley had slipped on the shaft on the expressway at
65MPH, or even while cornering and shifting on the off ramp, the story
would have been very different.

This is the only case I've had of timing radically changing.

Oh, when I reinstalled the head, I decided to go 50% or so over the
torque in Bentley.  Since then, I've overtorqued camshaft sprockets
which are not keyed.  Paranoid.


Val










...> 2. I had a 93 passat in here last fall, that had "quit" due to timing failure.
> It was failure of the "key" that keys the drive sprocket to the crankshaft,
> allowing the sprocket to slip on the shaft and get out of time. It had gone
> far enough that the valves hit the pistons and damaged most of the lifters.
>
> Couldn't figure it out until I noticed that when turning the engine,
> sometimes the T-belt would stay still. I thought the crankshaft was broken,
> but when it was apart, could see the key had sheared. It is not a
> replaceable key, but molded as part of the shaft. Built it up with weld and
> dressed it to fit NEW sprocket, replaced bent valves and busted buckets, and
> off she went. lucky no pistons were holed.
...>
> Sandy