Cam and Injection Timing Suddenly Advanced

[twentyeight]

My son and I were less than a block from home driving a consistent 40-45mph (2000rpm?) when suddenly the vibrations from the engine got louder and we lost a bit of power.

I rolled on home and noticed that the diesel clatter was markedly louder; vagcom confirmed that the timing was significantly advanced. At first I suspected the N108 but it checked out fine. After resetting the timing properly the timing tracks right where it should be.

I then proceeded to pull off the valve cover and found that the cam lock would not quite slide in because the cam was slightly rotated forward. I reset the cam and pump timing and it runs great again. It was out so slightly and I met zero resistance while rotating the engine manually that I do not currently suspect the valve train crashed, but I'll be getting a borescope to check for smoosh marks.

What I can't figure out is how the timing could spontaneously advance itself. It seems if anything slipped, the timing on one or more components would be retarded.

Has anyone seen this before?

 

[Abacus]

I'll bet your crank sprocket is slipping, which is a common issue on these models.

 

[twentyeight]

That was my thought too. I do have a (new) clutched alternator pulley, and to the best of my recollection was not decelerating, but that's the only thing that makes sense. Sigh. Apart it comes again.

 

[Abacus]

I'd confirm static timing and keep an eye on it first to make sure that's it. It should be able to go far enough to shut the car down all of a sudden but will get progressively worse if that's it. It'll show up easily by just checking the static (not dynamic) timing.

 

[twentyeight]

So I'm basically looking for the timing (shown under basic settings) to vary. Each start up, from when it starts to later on (ten minutes of running?), or to vacillate while idling? All of the above?

Assuming the D nose isn't too rounded out, how much risk is there of valves crashing? We have a trip through Northern Arizona and Southeastern Utah planned in couple weeks and it's really, really desolate up there. I can reset timing easily enough on the road, but munching valves would be a pretty big deal.

 

[Steve Addy]

So I'm basically looking for the timing (shown under basic settings) to vary. Each start up, from when it starts to later on (ten minutes of running?), or to vacillate while idling? All of the above?

Assuming the D nose isn't too rounded out, how much risk is there of valves crashing? We have a trip through Northern Arizona and Southeastern Utah planned in couple weeks and it's really, really desolate up there. I can reset timing easily enough on the road, but munching valves would be a pretty big deal.

A shifted crank sprocket will radically change the timing, not just vacillate like you see in vagcom when you pull up the tdi timing graph. The fluctuations on the graph are typical and pretty close to where timing has been set.

When the sprocket shifts it'll change the timing to a completely different place on the graph.

I would not risk a long distance trip if I knew my crank sprocket was moving around. I'd want to take care of that before I left town.

My .02

Steve

 

[mojogoes]

If the crank pulley sprocket location notch has warn slightly it will do as the op has described? I was very fortunate at one stage where there was only a millimeter or two left on my sprocket wheel , by this time i was setting the timing on a daily hourly basis lol.

I remember just afer picking the car back up and turning the ignition off at a fuel station , that the car let out the most loudest ))))))) Bang ((((((( backfire id heard from a diesel motor lol

The sprocket bolt may seem tight but if there is any play in the location notch , under load it can still move especially if the motor has been hopped up with fueling mods.



The slightest sign of unexplained low amounts of power loss as in the car didn't seem to be quite as peppy / fast on that drive! can be the onslaught of the dreaded crank sprocket movement.





P.S. I guess it could also be the wiring to the ip from the ecm or a No3 injector/wiring failing or ip.

 

[Steve Addy]

I kind of wish now that I'd pinned the crank sprocket on my AHU in the B3V wagon. This whole issue makes me very nervous..

Steve

 

[twentyeight]

I wish I had pinned it too… this engine only has ~4000 miles since being rebuilt. I know I got the whole 90° torque angle out of the bolt, but now I'm wondering if the clutch slipped and the engine moved without me noticing. I'm kind of grasping at straws to come up with an plausible explanation at this point. If the cam and pump both moved then it has to be the crank that slipped.

I think I'm going to go ahead and de-tension the belt and remove the crank pulley for inspection. Bora upgraded my shipping and the new sprocket and bolt will be here tomorrow morning (thanks Aaron!). It's only a high of 100° on Friday instead of the 112°*on the day this happened.

 

[twentyeight]

I remember just afer picking the car back up and turning the ignition off at a fuel station , that the car let out the most loudest ))))))) Bang ((((((( backfire id heard from a diesel motor lol

That would almost be worth it to hear!

The sprocket bolt may seem tight but if there is any play in the location notch , under load it can still move especially if the motor has been hopped up with fueling mods.

I almost regret running the 11mm pump at this point. It does run very very smoothly, but if the increased tension on the timing belt means more wear and tear, it's difficult to justify for a road trip machine.

P.S. I guess it could also be the wiring to the ip from the ecm or a No3 injector/wiring failing or ip.

I actually got my scope out and watched the duty cycle on the N108 because I suspected the piston got stuck full advance. I did get a code (00550) complaining about the timing. Just another good reason to keep the MIL off and to promptly check the codes when it comes on.

 

[Abacus]

Every crank sprocket I've installed has never had an issue again, probably because I use the Bentley specs. If you do remove it, just do it right and I wouldn't worry about it again.

 

[Digital Corpus]

300 ft*lbs or torque and low fuel economy from using it and mine hasn't budged from the day I put it back on permanently specs like Abacus has said.

As for how much wiggle room there is, I have successfully dyno'd plus and minus 2 flywheel teeth to advance and retard the camshaft without a problem.

 

[twentyeight]

I got the sprocket off. It was surprisingly easy with a 3-4 ft cheater bar.
Lots of oil. Maybe too much?

There's a small amount of galling on the crank nose. The sprocket looks fine. Maybe my torque wrench is inaccurate at 66ft/lbs? Maybe I should try going to 70ish? (Plus 90° of course)

Photos here: http://imgur.com/a/mMTDC

 

[twentyeight]

The old sprocket had a small amount of play without the bolt tightened. The new one is much more solid. Torquing was more challenging than I remember, but that might have been a clearance issue; the front end was off the last time. I'm hoping that it was just a case of inadequate torque on a worn sprocket (though the bolt was new). Time will tell.

Unfortunately I found the timing belt tensioner bent slightly. This isn't my first timing belt job so but I'm not sure what happened. I have a new tensioner on the way just to be safe.

 

[Abacus]

The crank looks ok, although I like to clean them up a tad.

They're a pain to get off when torqued properly, so that was probably the cause. A few ft-lbs either way won't make a big difference so 70 should be ok, it's not like they require a micrometer.

Curious as to the TB tensioner, you're tensioning it the correct way, right? Gassers are opposite.

 

[twentyeight]

OK, got it all back together. Turned the tensioner to the right (clockwise). The last one was Ben's along the stops as though it was turned backwards, though. I can't believe that I would have yanked on it backwards, so I wonder if that's a symptom?

Anyways, it's running well again. Hopefully nothing more for the next several hundred thousand miles