M276 timing components replacement
 

Has anyone torn into the timing components of a m276 (m278) engine yet? At 253,xxx miles I've changed the timing chain tensioners but just every now and then I get a heckuva rattle. It cranks and runs fine. I get the following codes:

The pos of exh cam bank 1 deviates from the specified valve. Implausible signal.

The pos of intake came bank 2 deviates from the specified value. Commanded position cannot be reached.

The first code is not there all the time but the second is. I just purchased a GL450 to have as a spare car (needed three rows to haul grandbabies). This will give me an opportunity to get the GLK in the shop and break it down to see what is up. It is now at 253k miles, uses no oil and has always had 7500 mile oil changes using Mobil 1 changed hot:). Based on what I've read I'm thinking at least the intake on bank 2 cam adjuster needs to be replaced. Once you remove the covers you can see if the adjusters have issues while turning engine over by hand. I'll start there over the next few days.

I'm thinking with the type chain design they should be good for 300k miles. Any thoughts on that. There is a kit you can purchase off ebay that has all the timing components, new tensioners, chains, guides and all four cam adjusters. I have not decided if I'm going to go with something like that because I'm assuming it is made in China. The cam adjuster from MB is $1000/each:eek:
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There is a kit you can purchase off ebay that has all the timing components, new tensioners, chains, guides and all four cam adjusters. I have not decided if I'm going to go with something like that because I'm assuming it is made in China. The cam adjuster from MB is $1000/each:eek:
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never had 1 of those apart but as complicated as it is, i would never cheap out on the parts. dealer or the oe brand vendor only.

Is it possible the lower chain tensioner is the source of the noise. That would mean the whole cover comes off in order to inspect.

The cam adjusters on those engines are absolute garbage. If you've got 253k on them you're WAAAAAAAY ahead of the curve.

There is a TSB (Xentry tip) that calls for installing a check valve to reduce rattle on startup. Do you have it?

Yes check valves are installed.

Thanks for replies. I'll eventually break it down to see what is up.

Your timing chains are stretched at that mileage, they are only good on average to 170k miles, take the upper cam covers off and show a picture of chain tensioner piston , may be extended too much

Got the covers off. Everything is lining up fine. I did find one of the cam position sensors connectors loose and I may have had a leaking intake gasket. Not finding anything out of line in regards to timing. Bank 1 tensioner is sticking out further than bank 2.

Here are tensioners. Bank 1 extends out more than bank 2.

The fault code was on bank 2 cam timing not at desired. Also I was getting an out of range high indication on the intake manifold pressure.

Before I started disassembly it threw a check engine light, rough running and smells rich running. Misfire on 5 and 6 and the intake manifold pressure sensor was showing a number higher than spec at idle. I did find a cam position sensor connector may have been loose and one of the intake manifold gaskets had a tear in it (possible leak).

All of the timing marks are lining up. Once the cam hold tool arrives I'll pull cam covers to see if I can tell anything else about it.

The fault codes came up once the wife stopped (engine running at idle) after having been on the interstate running fine at around 80 mph for about an hour.

I'm going to proceed with replacing the cam adjusters and all the chains and tensioners. hopefully it will make it another 200k miles:).

Yes the pictures show your chains are stretched enough to warrant replacement, did a car with same issue, i measure the tensioner stick out 10mm approx, thats enough, on a 278, my own 104 wagon engine with 225 k miles showed 12 degrees stretch, had low torque but high reving power , after changing it lots of torque returned

I had a good day on it today but unfortunately found the #6 cyl intake cam lobe closest to firewall worn. I'll get the passenger side valve cover off tomorrow.

surprised to find this
 

I stay on top of the oil changes using Mobil 1 0W40. This engine has 253k miles on it averaging between 70 and 90 mph for most of that time. I've been changing oil at around 7500 mile interval.

rear lobe on #6, or last lobe on intake, bank 2.

This was only lobe like this. I wonder if a failing cam actuator could possibly have caused low oil flow to this lobe?

I meant to mention this is not that much of a job but there is a lot of stuff in the way that has to be removed to get to what you are working on.

Cyl 4 also had issues with the cam lobe/roller. I got the front timing cover off and it looks like I am going to need to pull the heads to replace timing chain/guides. I would have come out cheaper finding another good, used engine.

This engine makes me like the 1998/99 E300 m606 that much more:rolleyes:.

I've been reading a lot of stuff about the 276/278 and was disappointed to find out that the oil pump is manipulated. I've never been a fan of variable flow oil pumps and have seen cam issues on BMWs that had this set up. It is done for energy savings is what I understand.

I'll be pulling the heads this week. Seems they have to come off to change out the chains, guides, etc....

If someone could please post the torque specs for the head bolts it would be much appreciated. I've got an older copy of WIS and it does not have this application on it. I have got a newer copy coming.

tia

I'm thinking that a combination of a bad cam adjuster and a variable flow oil pump is what damaged the cam and three rollers. If anyone knows how to disable the variable part of the oil pump and could post it I'd appreciate it. I don't want my oil pump to back down for nothing.

Finally starting to go back together.

Got heads bolted back on this afternoon and noticed the rear lobe on the exh cam was boogered up some so I ordered another cam. I'm not that impressed with this engine. Am I being unrealistic comparing it to the 606 in longevity? I don't care if it is a gasser I would not have expected to see the cam lobes chewed up some.

No, you're not in my opinion.

The variable displacement oil pumps are used in quite a few engines nowadays and, like you, I've always been a little queasy about their adoption.

I've noticed on the oil pressure gauges of more modern cars when at high-speed the oil pressure gauge is showing half scale readings. I kind of like looking down and seeing the oil pressure gauge at 80-90 PSI full scale readings like my 98 Dodge truck with the Cummins engine.

Of course there's no way to definitively prove the variable displacement oil pump was the cause of your cam wear, but I'd certainly say it's a possibility. When the engineers are calibrating the operation I'd guess they're more concerned about extracting an extra 2/10's of an MPG to comply with an EPA fleet mileage requirement than they are about the owner of the car 300K miles in the future.

As I recall if the sensor that measures oil pressure fails the pump is supposed to default to full-flow, maybe you could just unplug the right sensor and force it into full displacement?

Thanks Tim.

I should fire it up sometime today.

I think it is the combination of the cam adjuster going bad (maybe allowing more reduced oil pressure to cam. and then the oil pump reducing flow may have led to what I'm seeing.

It was the lobes that had the indications on it. The cam bearings looked fine.

Just finished up. No more cold start rattle:D. Starts, drives and runs out good with no cam timing fault codes. I ended up replacing both cams on bank 2 and about four or five of the roller followers. I purchased the ebay kit for the four cam adjusters, timing chain(s) and guides for $860. I could not bring myself to purchase four new MB cam adjusters for $1000/ea is reason I went with ebay kit.

Should be good to 400k now.

My next step is going to be to see if I can disable the variable oil pump system. I'm thinking to hook the scanner to it, watch the oil pressure, disconnect the connector that to the oil pump solenoid and see if pressure stays up the entire drive.

I'll let y'all know what I come up with.

Can anyone provide a definitive answer regarding whether the oil pump defaults to "normal" flow/pressure or to the "reduced"flow/pressure when the oil pump solenoid is disconnected?

I can't imagin them defaulting to the reduced flow/pressure but you can't tell these days.

I disconnected and covered up (to protect) the connectors to the oil pump solenoid. Road test and only fault code was this system had electrical fault/open circuit. I'd rather my oil pump stay at the higher rate.

interesting
 

I'm probably going to hook it back up today. The mpg has dropped a good bit since running it unhooked. We have, for a very long time, averaged at least 24 mpg, running it for a few hundred miles since I disconnected it I'm down to 20.x mpg.

I read one time how much hp an automotive oil pump uses up and it was higher than I would have ever imagined.

I did a quick run to the MB dealer (150 mile round trip) and averaged a little over 22 mpg. I hooked it back up after getting back. I'm still on original O2 sensors so if I don't get back to 24 mpg after hooking them back up I'll change them out to see if that will help.

Keep in mind that lower ambient temperature will impact fuel economy. Since you've been off the road for a while these late December temps may be to blame....

As I recall it's supposed to be something like 4-5% power savings? Pretty significant savings when you're chasing corporate MPG requirements.

I also seem to remember from hydraulics that pressure relief by-pass valves generate quite a bit of waste heat.

If properly done it seems like variable displacement oil pumps are worth the trouble.

That was my conclusion too Tim.

Now with that said, and I'm going to put it out there for anyone else that ever has to pull cams from the M276/278, go ahead and replace all of the cam roller/followers while it is opened up. Easy to do with the cams out.

The cam was not damaged at the bearing surfaces (indicating no loss of oil) it was damaged on the lobes. That was either caused by the timing adjuster being worn out jacking the cam around or the roller/follower going bad. I did find indications on a couple of the roller/followers where there was no cam lobe damage.

Hey, read the whole thread. 253k all those issues and still tanking along, amazing. Gives me hope. I have a 13GLK with 136k, and even after new adjusters and tensioners (with check valves already behind them) I've still got the rattle at startup, from chain stretch I surmise. However idle at startup is much improved with the new adjusters.

Did you really have to pull the heads to swap chains? And did you ever find a video or instructions for the entire procedure? I saw a video on YouTube with the front of the motor, covers taken off all the way down to the crankshaft. Made it look like it was possible without taking the heads off.

She still going good? How many miles did you go with the rattle? I know the slap will eventually screw the adjusters. It's a shame there's not a ratcheting tensioner in there to save from this much work.

Heads have to come off. At 274k miles now. Did a 3000 mile round trip ride to El Paso in May. Still runs good and averages 24 mpg.