When I worked at Borg Warner we were designing variable cam timing mechanisms. We talked a lot about "cam torsionals", which is a torque that comes from how the followers ride the lobes of the cams. There is a torque needed to twist against the lobes, but when you reach the peak of the lobe, it actually wants to shoot forward and you would have to twist backwards to prevent that. Picture rolling a barrel up a hill and then cresting the hill - the barrel wants to roll away down the other side. This is happening many times per second while running, and it sets up oscillations in the tension of the belt, or even chain. We only worked with chains.

These torsionals are very high in inline 4 cylinder engines, compared with other cylinder layouts, and I think they are the cause of some of the belt slip we are seeing. It's not an issue of cam or crank inertia, but improperly installed belts, long runs of belt with no idler, and cam torsionals that make the belt jump around a lot.

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Interesting, makes sense. Might be a compound problem with a somewhat worn bearing and an old stretched belt leads to the slippage.

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simply because you got to it in time.

Keep in mind:

oil pressure is tied to RPM

you mentioned that some of these failed at idle and while coasting down.....

with the bearings so far degraded that rollers are flush with the stamping the the rockers, it's possible at low rpms, with low oil pressure on the lifters, with the vehicle making a turn, or taking a bump, that after the valve closes, with the cam lobe pulling away from the rocker, that the rocker could slide off sideways...... but before it gets a chance to "get completely out of the way" of the lobe, the next time around it comes down and hits it sideways, breaking it.


I still don't buy into the "timing belt snapping back into it's original position theory" but lets say for a minute that it's true....

when does it snap back? the rockers are not going to get damaged simultaneously, there going to get damaged sequentially....

At any one time, the valves are doing different things..... if the "impact event" supposedly snaps everything back into it's original position, you would only see damage to valves that are synced, and being a 16 valve motor, in theory the damage should happen in pairs, for example both the intake valves to the #1 cylinder (because they would both be hitting at identical times)


I still think it's soot caused by EGR and ring / valve seal blowby..... and the best way to deal with that by far is a bypass filter....

more evidence of this: you said the exhaust valves are always a little worse. Being a turbocharged motor, there is ALWAYS going to be pressure in the exhaust manifold / exhaust runners, that means that there will always be a little bit of blow-by through the exhaust valve guides / seals... the same steel spends some of it's time in the oil, when the valves up, as it does in the exhaust when the valve is down.

the means that the exhaust valves are going to be exposed to a little bit more contamination in the oil than the intake valves are, hence why their bearings appear to have degraded more...

The other possibility is carbon build up on the pistons due to EGR and PCV mixing together.... but you guys would have all figured that out when you pulled the heads, correct?

I mean you would have seen valve impacts in the carbon (on the tops of the pistons).......

Right.....but then why it the failure happen so suddenly? Maybe if the engine ran longer they would come off, I don't disagree there, thats certainly possible.

But again I ask you, how does an engine go from running perfect one minute, and then the next running like crap the next, backfiring out the intake, misfiring, no power, showing even wear across all 8 exhaust rockers, and showing even wear across all 8 intake rockers, having no rockers popped ONLY by having bearings wearing?


You take issue with my theorey that the belt gets pushed back into time, I agree its odd, I'm not sure thats how it happens, but its still my best idea.

You take issue with the idea that the rockers are all damaged simultaneously, and that it should happen in pairs. I understand what you mean, if the very first time the rockers hit and it "pushed" the belt back, the damage should stop there.....but what if that act takes 1 second. At 750 rpm(near idle) that is 12.5 rev/sec. That means in that one second the engine has turned over 12.5 times. Thats plenty of opportunity for all the pistons to impact all the valves.

Keep in mind:

oil pressure is tied to RPM

you mentioned that some of these failed at idle and while coasting down.....



Again, these are rockers that did not slip off, and haven't physically broken in half.




I don't agree with that. The oil getting pumped through the valve cover is all coming from the same place, I don't see how any valve stem seal blowby could contribute to the bearing way up on the top of the cam.

You could make the argument that because there is a bit of exhaust residual after the valve has opened that the bearings are under more force all the time, and which then since they are all under more force they all wear a bit quicker than their intake counterpart. Which could explain why the exhaust rollers are always worse than the intake.


Lets back up for a minute and look at this situation from the start.

Someone is driving their CRD, all of a sudden it starts running very rough, backfiring through the intake, very little power, etc. We pull the valve cover and find rockers with trashed bearings, ALL the rockers still on the valves, and then using the VM tools we find the engine is still correctly timed.

Right now we have two explanations.

1) An old belt stretched/slipped/jumped/voodooed its way off long enough to cause the damage.

2) Years of wear with soot contaminated oil has worn the bearings, finally causing the engine to run so poorly.


The problem with explanation 1 is that its hard to account exactly how the belt skipped, allowed a little bit of contact, and then slipped back into place. If the engines were always off a little on timing we could buy #1 easier.

The problem with #2 is that is doesn't explain the sudden dramatic failure of the bearings. If we had degraded performance over time that slowly led to a bad running vehicle that would make sense, but when something happens suddenly its harder to explain how something could degrade for so long, show no symptoms, and then sudden leave a vehicle that will barely move under its own power.


You can't see how the belt would jump back into place, I can't see how the slow wear of the bearings would cause such a sudden symptom onset(where there are no rockers off).

It would be different if we had an engine that the timing was off. It would be different if we had an engine with rockers off. But in this case neither are.

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mine was running okay before I pulled it apart... I pulled mine apart because of the head gasket.

at full throttle, I got a lot of black smoke, but now I realize now it's because 2 of my intake valves (one on #1, one on #2) wern't opening....

I even towed a #5000 boat about 100 miles like 2 days before I started wrenching on it....

diesels make their power from fuel, not so much from air..... if it were a gasoline motor I'm sure it would have been way worse on power, but theoretically I was still getting 50% of my air to both those cylinders....

Well then your case is a bit different from all the others I have come across, and I'm not sure what to tell you.


But again I ask you, how does an engine go from running perfect one minute, and then the next running like crap the next, backfiring out the intake, misfiring, no power, showing even wear across all 8 exhaust rockers, and showing even wear across all 8 intake rockers, having no rockers popped ONLY by having bearings wearing?

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I'm the kind of guy that likes to improve on things.... this is bugging me, I want to figure this out and fix it.


if it's the belt interval, great, it's a self correcting problem.
if it's EGR, great, I'm getting an eco tune and installing a block off plate.
If it's something else, I want to improve on it (bypass filter maybe).

if it's none of these, I'm going to fix it, sell it while it's still worth something, and go buy a toyota.....

I love to improve things too, thats why I have been running the EHM, ORM, from day one. My intake is nice and clean.

I reiterate my question because you say you don't buy my theory, and offer your own theory. I have questions about aspects of your theory, and you do of mine, I have tried to answer them as best I can. I am willing to entertain the notion of your theory, hence my questions.

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Yeah, your sudden death point is a very valid one. I honestly have no idea....


the more I research timing belts, the more I learn they just don't stretch. if a used belt is easier to put on, its most likely because it's lost a percentage of it's dimensions to wear.

*sigh*

when you've been tearing these motors down, what did the pistons look like? no carbon, lots of carbon, valve indentations?

oh and what's EHM, ORM ?

Ya the sudden death point is what leads me to think its belts jumping around, I know its an odd explanation, but like I said its the only thing I can figure given the "sudden death" circumstance.

The engines I speak of were not torn down past the longblock, so I cannot speak to carbon buildup other than that there was some carbon buildup (noted from the injector hole).

The EHM is the elephant hose mod, the ORM is the offroad mod. Check out the noob guide for detailed explanations of both(they cleanup a bunch of these issues).

Noob guide:
viewtopic.php?f=5&t=54207

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recorded a quick vid and put it up an youtube.


http://www.youtube.com/watch?v=TEKrfFQdjQg&feature=youtu.be


That's wear man....

That pin wasn't hardened enough, or was made with sub-standard metal....

could oil contaminates have contributed? probably. but at the end of the day, those rockers are poop.

Now was VM aware of this? and have they since improved their process/metallurgy?

That motor is pretty popular in europe and around the world....

found this on youtube as well
http://www.youtube.com/watch?v=8ELktBoWozI

I have seen that "wear" before too on engines with the "sudden death symptom." I attributed it to the fact that the "event" for lack of a better term, was responsible for damaging the bearings, then causing them to wear quickly and unevenly like that. It possible that the wear combined with some other mitigating circumstances, like the belt slip theory, or the valve float theory, could lead to the perfect storm of these sudden failures.

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Go here to see pistons, the #1 piston has carbon buildup due to rocker arm roller wear.

http://www.davidhaggart.com/Autos/VM-En ... &k=SGpDNL2

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It is still strange that rocker failures are not common in Europe, Australia, Russia and everywhere else outside North America. The export market uses less EGR (less strict emission standards) and different spec oils based on average ambient temp. These rockers are used on on VM engines from 2001 through 2007. They might also be the same rockers used in the VM panther engine from 2007-2010. I doubt VM would be able to keep a common failure mode quiet in the service market.

In NA, the rocker wear will become a bigger concern as engines continue to age.

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I see you found my video.

Sent from my Nexus 7 using Tapatalk 2

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That wear is NOT from a single event....



here's a question:

I understand how EGR absolutely craps all over the intake manifold, but how exactly does it contaminate the oil?


Exhaust ---> intake it's a pretty simple route it takes...

I'm planning (in my head so far) a remote oil filter w/ bypass filter and remote oil cooler somewhere between the trans and the diff...

http://www.amsoil.com/catalog.aspx?groupID=56
http://www.summitracing.com/parts/der-15850/overview/


would solve all the world's problems.....

that's IF I decide to keep this thing...
I want proof that it's fixable permanently...

Try this. It may answer your question

http://www.machinerylubrication.com/Read/349/egr-oil-diesel-engines

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good read... even more evidence that bypass filtration and oil cooling is the answer to all the world's problems.





I tow a lot, and overheated to the point where I blew my head gasket....(the start of this slippery slope to expensiveness)

sucking out some serious BTU's from the oil would be good for everything.

I agree, but to be fair it seems that we have more data from the US.....because we have more reporting members from the US, than the rest of the world.......ie we have a sample problem.

For as many of these engines are running around in the rest of the world I don't know how I would ever hear that there was a problem with one.

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hey sam, you run a bypass filter?