S-Prihadi

Gents,

I been thinking, the most common issue with our VVT sprocket which user "defined" as BAD, is when that famous rattle noise happen at start up.
Upon investigation, one will find the locking barrel pin and the cavity for holding that barrel pin has worn out a great deal.
















I have always assumed that this lock only works during engine start, meaning when engine is OFF it locks and when engine running, it will unlock.



Oh boy, I was wrong. When engine is running, and when throttle is at minimum like when you coast or let go of the throttle, this pin actually lock back to its home position again , wow !!!

Here is engine OFF. Exhaust VVT will park and locked at -25* , while intake will park and locked at +33*





Engine start from cold will have higher RPM, ECM strategy controlling it. at 30 seconds into engine start from cold.




2 minutes into engine running from cold and idle RPM has settled down, the exhaust sprockets from various operational angles during higher RPM of first 60 seconds of engine start,
will then go back to its locked position by the time idle RPM has settled to +-600 RPM.
NOTE that both Banks Exhaust angle is not -25* anymore but at -23.20* and -24.78* is because of the adaptation/compensation the ECM is doing, so true angle wise they are actually -25* and would be in a LOCKED state.





Now the on the road test : EXHAUST VVT SPROCKET
See, when I let go of the throttle, this sprocket will go back to home base at -25*. Yes, this VVT test page does not have throttle angle data, but when exhaust VVT sprocket goes to a compensated -25*, that meant I let go of throttle pedal.



The same for Intake VVT sprocket, when I let go of throttle, it will head home to +33*



Below is the actual driving representing the 120 second of VVT Intake and Exhaust activity as seen on 2 graphs above, in a single page VVT test page of Xentry.



.

This means those with stop n go city driving as majority of his car mileage life, instead of a nice cruise control stable highway speed, will have his VVT sprockets locking barrel pin
be worn out sooner mileage to mileage apple-2-apple comparison. That is unlucky me and adding fire to misery, the my lead footed throttle pedal even at highway driving
will accelerate the damage or wearing-out even sooner


To me that sad truth is part of driving $$ expenses, it is not an issue.....it is given, just swallow it.
What I would love to keep track of is, how much "drift" of actuation degrees will a wearing-out VVT impeller or middle blade + the main assy oil gap tolerance will produce ?
I would worry more of my valves hitting the piston if my VVT sprocket goes bad and over or under shoot by much.

So, I think per oil change of 5,000KM, I would need to log the VVT test and observe how it is changing from normal to minor drift. 5 degrees would be a maximum drift I guess.
For those wanting to do the same, this VVT test on Xentry can only be done with a fast C4 ( BenzNinja reccomended one ), it can not be done using OpenPort 2.0 Xentry Pasthru due to slow 1 Hz logging.
I have both types of Xentry so i know.

Also I never yet seen any Launch or Autel or Xtool scanner having this VVT Test page.


This is OpenPort 2.0 Xentry Passthru result when doing VVT Test. Logging or processing speed too slow and I thought my VVT sprockets were bad...LOL











Sometimes data is missing too. See exhaust VVT





Oky doky..... that is the information sharing for today.

ADD, I am attaching the VVT Test log for anyone wanting to see in detail.
549 data points for 120 seconds logging = 4.6 data points per second per PID is the proper fast Xentry logging speed to properly log this test.
3rd party scanner is typical 1 data point per second per PID and probably the same for Xentry Passthru using Tactrix OpenPort 2.0 , even genuine one : https://www.tactrix.com/index.php?pa...ed=1&Itemid=53

.

Chevota

I cant say for certain, since I havent taken VVT apart, but I cant imagine it locking when running. I have always assumed it works on oil psi. Default is locked, oil psi unlocks it. Maybe not but I see no reason to lock when running. Plus timing moves very quickly, so if it locked, it would need to unlock first, and I dont think there is time. Locking only when eng has no psi makes perfect sense. That cam timing is normal for idle mode, and the exhaust may vary in cat heating mode. My idle mode can extend to 2krpm. Cat timing in idle mode changes Ex from the normal -25 to -15. Then there are normal and cat timing outside idle mode with it again trying to force -15 on the Ex and 36 on Intake for longer than usual.
These were bugging me because it pops in and out of cat mode all the time, so I set cat mode to be the same as normal mode, except when the engine its actually cold.

S-Prihadi

I agree you are right to say that that locking barrel pin is not actually locked, as it is floating off oil pressure when engine is running.
However, the degree value when the VVT is at home base.....which is also a locked position, puts the barrel pin above its locking cavity ready to go down ( has a spring ), anytime oil pressure is lost/reduced.
What I am curious to know is, how many millimeters upwards does the barrel pin need to stay afloat to be in zero contact with its cavity, to prevent significant wear.

If we see on different MB engines, the cavity is of a different shape/design.
Example this version of cavity has a nice sloping assist. Let say total cavity depth is 5mm, the actual lock capable cavity is only like 2mm and the 3mm is the slope.
So perhaps this cavity design only needs barrel pin to lift off 2mm and if not enough lift to full 5mm, that slope can assist, but with extra friction as cost.
Below is from M271 engine.




This design is different, it sure looks like maximum lifting up distance of the barrel pin is a must and there is no slope to assist. Let's say this one need a full 5mm lift of the barrel pin to unlock.





This one shows the barrel pin when the impeller/vane is at home position, toyota engine but same working principle. This one has return spring assist to send impeller/vane to home base degree/position.





The shape of the barrel pin and its cavity is like a bolt door lock action.


A kind of design which is so scary to visualize, for something which moves a lot and fast and only using oil pressure to lift off the "bolt" aka barrel pin.


The higher the lift off of the barrel pin above its locking cavity, the more sealing area is lost to support that oil pressure as the hydraulic lift up force.

One of the VVT sprocket will fail faster than the other one, I forgot which exactly.
Since the camshaft sprocket has inertia when spinning one direction, the VVT impeller/vane which oppose that spin direction will need to work harder....something like that.




.

Rickman30

The material is a standard non-hardened soft steel. There are rebuild kits for the M278 and others, that utilize a hardened stainless steel plate and tool steel pin. No one has confirmed if these will fit the M276 engines. I did see where a gentleman tag welded with stainless steel the plate then used a CNC to reshape the hole back to original shape and just flipped the pin to the unworn end.

I would like to do both my intake adjusters as the problem doesn't appear to affect the exhaust. Mine only rattles once every couple months or more. I've owned a year and have heard it 3 times. Even the chain rattle is only after the car sits for a week on cold start does it make a little noise only heard if door or window is open. I hadn't thought about it locking while running, as it is controlled by oil pressure, the pressure reduction strategy has effect on the pin/plate wear for certain.

If I was healthy enough, I would do this myself, save the CNC, but I will end up paying to get the bank one changed and the secondary chain tensioners as well as checking or replacing the check valves in the heads.

But I'd feel better with a harder steel than pay $1k for soft steel.

I took a cam capture on startup with my Thinktool Pro, I does show bank one intake adguster floating more erratic indicating pin not locked, bank two was smooth. And both showed tensioner oil pressure pump up as well

I tried to add captures but Apple is not friendly. Will try to get wife's laptop working, she hasn't touched it since she retired 3 years ago.

Again, Thank you S-Prihadi. Once again a wealth of knowledge shared.

S-Prihadi

This video is very informative.

At some point in time, MB made some revision. As such, by design, the plate with the locking cavity for the barrel pin is on purpose design differently for IN and EX.

Exhaust valve has to fight combustion pressure when it has to open, while intake valve is in fact assisted by minor "vacuum" when opening.
Combustion pressure is expected to be easy 700 PSI or more. That is a respectable pressure to overcome.









So the 63everything.com selling custom plate with the locking cavity design being the same for IN and EX, I find it strange or it isthe very earlier model of M156 VVT design.
https://www.63motorsports.com/m156-s...sters/p/stage1





This XF Motorsport youtube channel, shows one of his intake VVT worn out so bad, it sure looks like exhaust VVT cavity of newer design as what Tasos showed.



I am certain MB has gone thru a few revisions on their VVT design.
Below shows the XF Motorsport M156 is having the EXaust VVT without the slope assist.







=====================

This is from my friend M271 EVO engine. Built year 2010.
I just teardown it today for knowledge sake. It is the same, EX cavity have the slope assist where IN cavity has no slope.





The intake ( LEFT ) is the one showing wear.
This small wear alone can produce that rattle-knocking sound during cold start of after 30+ minutes of engine shut down.












There is a spring too. This spring helps to overcome the retard bias torque of the valvetrain.









.
The spec of the M271.860 EVO engine. EVO = Turbocharged
Oil pump is not a 2 stage design. It is the simple one, higher RPM = higher pressure.


The VVT spec


I could not find Introduction Manual for M271 non EVO, which is the supercharged one.
Usually there we will find the information on its VVT operation in greater detail on earlier edition of the engine.


So be careful when seeing the "slope" on the plate with the locking cavity. It could be MB newer design or a wear pattern on older engine looking like a machined slope

juanmor40

@S-Prihadi , are you aware of this issue https://mbworld.org/forums/c-class-w...ml#post8201503

S-Prihadi

That is the beauty of American market
In my country, nahhhh.......... them MB Indonesia wont entertain you.

Chevota

Seems to me that spring eliminates the need for the feed ramp for the pin. If there was no ramp it seems to me the problem would go away. So help me understand why the version with the spring has a ramp.
Even without the spring it seems to me that ramp is way over kill, and basically causing the problem. What am I missing?

Rickman30

Everything I've found, the "Ramp" is wear, it should not be there. That is where one would Tig weld with stainless rods and machine it back to factory condition, if repairing damage rather than replacing the adjuster.
The spring is when oil pressure drops after turning ignition off and oil control valve returns to rest position and ensures it locks into place for the next startup till oil pressure resumes.

Simplified explanation, others can give exact technical explanation.

Rickman30

Not all dealers are helpful, some want to do just basic maintenance and lite warranty work on new to three year old cars. I was quoted $1200 just to tell me if one of my camshaft adjusters was making noise...

S-Prihadi

So next mystery to solve is :
Did MB actually made that ramp/slope on purpose for Exhaust VVT at some point when they keep updating the P/N of the VVT sprocket on their engine lines ?
or simply its a beautiful worn out pattern ?

Do note, there are 2 kinds of VVT sprocket when it comes to how the oil control valve is positioned.
M156 oil control valve is not in the middle of the VVT sprocket, where M271, M276 and M278 has the oil control valve residing at inner diameter of the VVT sprocket.

M156. Item 230 is the oil control valve for VVT which is a combo duty. It is oil valve with its own actuator.




Our M276 or M278 oil valve is a stand alone oil valve only, the so called magnet or actuator is separate. I guess this model of VVT some will have that spring.






I used 20x magnifying glass to inspect the nice slope/ramp of the M271 EX VVT and that is not a wear pattern, that is a nice machined slope as explained by Tasos.
If anyone done VVT sprocket replacement in great numbers like 100+, Tasos of Dubai is one of them.

Rickman30

Out of all the pictures I’ve manage to come across it was obvious the ramp was wear. it doesn’t mean that some may have been purposefully made with a ramp as you have stated, and an experienced installer would obviously know better that I. I can only go by information at hand, and you have provided more for the puzzle. Here is one site providing rebuild and upgrade kits for some of the VVT adjusters, It has some clear pictures of the lock holes in question. One thing I noticed was a relief slot I assume is for oil to escape when pressure is absent, engine off, and not impede spring pressure of lock pin.

https://www.63motorsports.com/m156-s...sters/p/stage1

That being said, I don’t know everything, but I am trying to learn, and appreciate any help or "constructive" criticism. I say that as some feel the need to correct common terms being used or complain of the lack of technical details in "layman's" explanations.

Thank you S-Prihadi, information is good, but is nothing without experience and explanation.

S-Prihadi

I got M276 3.0 turbo video on its intake VVT teardown, it would be the same general design as M276 3.5NA.
It has a spring too like M271

On other M276 VVT vidoes, it is always the intake VVT too which is the bad one.















This M276 3.0TT intake VVT wear is worse than my friend's M271 Intake VVT, based on the locking cavity.
My friend's M271 do not yet have the DTC for the camshaft angle out of whack, only very loud rattling noise at cold start up.









Since there is no google translate on this particular video, I do not know if this intake VVT also rattle upon cold start up or not.
I would think it would.

The problem is worse than simply rattling at start up.
The VVT internal wear already to a level where target angle can not be achieved.












====================


I took a deeper look at the M271 VVTs, since now I know it is 99% identical for its internal to M276, except the size.
This 4 cylinder in line M271 VVTs has rattling noise from intake VVT too, but both get replaced and so are the oil control valves and chain tensioner. The magnetic actuator was kept as is.
I could not re-assemble back the INTAKE VVT, its spring pre-tension is too strong, so I did not re-assemble it back . I can only install 1 bolt and the other 3 were off target.
The EXHAUST VVT spring pre-tension is not too bad, but still need to fight it if I want to re-assemble it back as in having all 4 bolts able to be inserted and tightened.





All photos below is perspective : if the VVT is seen from flywheel/rear towards front of engine/pulley. So the engine rotation seems CCW and not CW.





From photos below, that is what I mean by INTAKE VVT spring tension is so strong, while EXHAUST one is not.
This VVT is about 20 degrees of movement , CAMshaft degree. The INTAKE VVT spring is "pulling-out" the locking barrel pin that much, probably 15 degrees or so.
I use the bolt to mark where the locking cavity is at.











Below illustration is : if seen from in front of engine pulley towards flywheel.





So the intake VVT is under approx 50% spring tension when it is in locked position, while the exhaust VVT is like 5% under tension only.

When in COLD start at 30C / 86F, the INTAKE VVT is locked by ECM up to 2 minutes until idle RPM settle down to +-600 RPM.
The exhaust VVT is the one being variable operation from cold engine start. Max RPM for cold engine start on my engine is 1,350RPM.





Without going into the wear and tear of VVT in terms of its limit for internal oil leak-rate which will be the root cause of failure to maintain target angle,
I think Intake VVT strong spring also play a part in accelerating the wear on the locking cavity and the locking barrel pin too.

This is the direction of travel of the intake and exhaust VANE in respect to the VVT assy or the plate of locking cavity, I marked as WORK
The plate with the locking cavity belongs to the main VVT assy, the one with the timing teeth.








When engine is running, the power mover of VVT complete assy is the main VVT body with the timing teeth. The timing chain is the prime mover.
This one :



Seeing the Xentry data where INTAKE VVT is locked at +33* during engine start, imagine the load the INTAKE VVT locking system has to endure.
01. There is a strong spring to "pull" the locking barrel pin away or out-of from its cavity.
02. There is spinning inertia of the VVT itself in the direction also stressing the locking system.

A is also the rotation of the engine
So before oil pressure build up enough to flood C chambers and offer hydraulic force to help INTAKE vane to stay locked at position B, the INTAKE vane have to endure main toothed assy A rotation pushing on it,
while at the same time the spring wants to rip off locking barrel pin from its locking cavity too. Quite a stressful duty.



So the ratting at cold start up is almost always from INTAKE VVT and not EXHAUST VVT.

EXHAUST VVT direction of work is supported by the direction of inertia and is supposed to be unlocked anyway, and having that slope/ramp assist it has a much relaxed life
during engine start up. So here I can say with certainty, if you tear open a brand new M276 exhaust VVT current version, that slope/ramp is on purpose there by design and is not
from wear. It would have cavity wear someday, but INTAKE VVT will suffer first.



Now, aside from surface tolerance of VVT components still within spec and does not allow too much oil leak and causing VVT to deviate too much from target angle,
what if the oil control valve itself has worn out to such an extend that it can not flow the oil enough or stop the oil enough ?

Ability to stop oil flow means it allows the locking barrel pin to stay pushed down by the super small spring at one side of the chamber where no oil supposed to be at
or else the oil will cause lifting up of locking barrel pin from oil pressure and unlocked itself when it should not.
While on the other or opposite chamber will have oil in it , to enforce pressure to keep the vane from moving and in return it helps the locking barrel pin too.




The "compression blade" of the VVT vane. This is like piston ring to a piston.






Some ECM has the ability to show how many % duty cycle is being fed to the magnetic actuator which control the full mechanical oil control valve, but M276 MED177 ECM does not have that data.
MED177 ECM only has target angle and achieved angle of VVT. Duty cycle is easy to get from any DMM having duty cycle or using a scope.

Good thing I tear-open the M271 VVT assy. Now that I know it will be very difficult to re-assemble this device ( INTAKE one worst ) if ever I get itchy and tear-open my own VVT
I seen some people use air pressure to lock/unlock VVT locking mechanism. Perhaps that is how the OE assemble this, special oil or air based assistance to push the VVT vane to be in locked
position before they can tighten the 4 bolts.

I think this is another reason why only M156 VVT replacement locking cavity plate is easily available, it has no spring to make re-assembly difficult.
If M157 the VVT seems to be like M278 and that means its basic design is like the M276 too.









Master Tasos has confirmed, M157, M278 and M276 uses the same VVT design.



So I guess to data log VVT wear and tear once per year or 5,000KM for me, aside from doing the Xentry specific 120 seconds VVT test with CSV file log, perhaps logging duty cycle of the magnetic actuator is a good idea too.
If the duty cycle goes up too much, 3 possible wear and tear scenarios are in progress.

.

S-Prihadi

hahaha..... I know what you mean

S-Prihadi

This is oil pressure build up data, but my COLD is only a warm 30C / 86F oil and ambient temperature.
In a 10C / 50F ambient or oil temperature, it would be slower to build up oil pressure.

I would put 10PSI as minimum oil pressure to assist VVT to do its work, at idle RPM.


Albeit the 2 stage oil pressure valve on my engine is not defeated yet during this data capture, the ECM during a cold start will not make 2-stage oil valve reduce pressure. That is the given ECM strategy.

Note, I should have added 1 more data point up front where RPM was still zero. So you guys need to add 0.2 seconds ( 1 data point ) to see how late the above 10PSI oil pressure is reached.





NOTE : When engine is already hot, the 2 stage oil pressure valve will be activated to REDUCE oil pressure, even during initial engine start.








So if I add the 1 extra data point or 0.2 seconds.
During COLD engine start at 30C / 86F, VVT will get 12.14 PSI by 4 second. During HOT start it will be in 3 seconds to hit above 10PSI.
However, the oil pressure sensor location is at Bank 2, where the engine oil filter is at, at engine block test port for oil pressure, so there could be a slight extra delay for the oil to actually
be at above 10 PSI if for Bank 1 VVT system. This is also probably the reason most common issue one finds in utube with Intake VVT is at Bank 1 being the one to be rattling first.





Oil pressure sensor location




Not the most fun install location if your engine is 3.0 Turbo with aftercooler like mine.

S-Prihadi

I was looking at Utube, using the search "camshaft rattle cold start"
Basically all manufacturers , even the conservative Toyota, will have the VVT locking pin issue.

I came across a unique video, it is about Ford.

It is unique because Ford made a drastic change for their VVT.
The techy also mentioned he has the rattle with the INTAKE VVT and his tear-down unit, a used one as example is the EXHAUST VVT
He also tear-down the new INTAKE VVT and exactly the same issue, he need to figure out how to fight the spring upon re-assembling it or he will have to eat it ( pay for it )

I think we all must accept that this VVT is like a manual clutch car, the clutch disc it has a fixed service life.
As with GDI carbon built up, it will happen, but some engine has less of it per say 50,000 miles driven and drive-ability issue will happen at much higher mileage for engine with better
carbon build up management. Toyota and Ford now is already using GDI + Port Fuel Injection combo to reduce this carbon build up.

Anyhow, I took a look at my 2018 EPC to see how many P/N updates has my VVT gone thru. It is 3 times already.



Since the VVT on my engine is the gen1, new P/N is the Gen3 but looks exactly the same.
On my engine , gen1 vs seller's gen3




What I can't yet phantom is, why is FCP Euro selling this genuine VVT at insane price ? US$924 is more than highway robbery by MB HQ.
Since the number is different compared to my EPC, I think this is a Gen4
https://www.fcpeuro.com/products/mer...mer-2760503200

INTAKE - RIGHT - BANK 1
On engine >>>>>>>>>> A276 050 20 47
EPC P/N generations :
A276 050 20 47 Gen1
A276 050 32 00 Gen2
A276 050 37 00 Gen3 CURRENT per EPC 2018
A276 050 52 00 Gen4 at FCP Euro