ML350 3.5L Balance Shaft Failure
 

What a surprise!.. Wife's '06 ML350 had intermittent CEL. Last year, dealer replaced cam / timing position sensors. Problem continued to occur with CEL coming on even more frequently. NOW, they tell me that the Balance Shaft has a bad gear and it is deteriorating. 73K miles. Thank goodness for extended warranties. Finding from other web site threads and blogs that MB USA is not consistent with the treatment of customers... some customers are bearing the full cost of the repair while others are being offered "good will" discounts. Appears there had been a service bulliten out for 2 1/2 years on this problem with no sign that MBUSA is stepping up to cover a known fault. roughly 10 updates to the bulliten adding vehichles to the list.

Any other Shop Forum members experiencing this? Not exactly the kind of news one expects when you take your late model Benz in for a CEL... "Oh Mr. Customer, we have to take your engine out and apart.... 5 days and $5K later... good as new"

And... What's to prevent the replacement components from wearing out the same way?... ie...is the problem "really" a faulty crafted part or is it a design issue?"

Finally. what other 06 models have the same 3.5L installed? the R, E, C classes ?

The first run of production motors had a balance shaft gear that was too soft, and in turn the chain would wear it out prematurely. The new updated balance shaft gear has not shown any isssues.

Please explain what a balance shaft gear is. Never heard such a term before. Are you referring to a vibration dampener?

Its the gear that is mounted to the balance shaft. the balance shaft helps smooth out the v6 motor (believe it is a 90* V6, due to the modular construction) by using a counterweight. The gear is driven by the timing chain.

Not just ML's but all MB's equipped with the M272/M273 series engines from 2005-08.

That is 1 of many reasons MB now suggests a maxi mun oil service of 10K miles as well.

Worn gear replacement
 

I just had this done to my 2007 GL450, under warranty thank heaven! :eek:

It was a shock to visit the dealer and see my *new* GL sitting there with a gaping hole in the engine compartment! :eek: :(

Thankfully, they really took their time and the tech working on it was a senior tech with experience. They had already done a few of these. They replaced a few other items there as well, everything covered, including all the solenoid units. I took a look at the engine afterwards with a critical eye and things looked really good, nothing out of place.

I asked the tech if there were any stray bolts left at the end, he just gave me a look...:D

Talk about a massive job for a tiny part. He showed me the worn gear, the teeth were visibly worn, substantially so. The engine appeared to be in excellent shape otherwise, everything clean and no signs of wear.

Oh, and they also fixed my wouldn't-stay-shut coin tray. :P

C.

Are the shorter intervals supposed to help prevent wear on this part?

Any more insight on the M273 I should be aware of Doc? TIA.

Got the wife's ML back today... so far so good. The rap sheet i 5 pages of R&R this, R&R that, plus a list of every sleeve, seal and bolt you can imagine... Also replaced Oil Bump & pick up tube, balance shaft (of course), chain tensioner, cam plugs, valve timing solenoid units, every fluid that flows through its veins.

QUESTION - what's up with filling the engine with Mineral Oil, running, draining then changing the oil again and replacing the Mineral Oil with typical Synthetic ? just curious what's special about MO?

Finally - what would happen if one did not have this issue resolved?

Using regular "mineral" oil is FINE...but oil change interval needs to be 5K miles not 10K!

Also in cold weather you might need to run lighter weight oil.


The timing chain can jump & bend all of the valves! Plus you wouldn't pass your emissions test.

Exact same here, it's obviously the same procedure at all dealers. Same parts replaced, etc. They also did the multiple oil changes. I'm guessing that they do the initial quick run and drain to flush out any contaminants that may have entered the engine during the R&R. Hence the use of cheap oil. Since they are only using that oil change as a flush, why use full synthetic? Makes sense to use cheaper oil. Then they verify operation and no codes and then fill up with the proper oil and filter.

On one hand, it's sad to see such a beautiful piece of engineering in pieces! On the other hand, the engine gets an early mid-life inspection and you get all fluids changed (like compressor oil, refrigerant, antifreeze, etc.).

Here is what the offending part looks like and comparison pics:

Here is a link to the attached TSB document for your viewing pleasure:
http://www.motor-talk.de/forum/aktion/Attachment.html?attachmentId=681441

Thanks Darktech, useful info.

Ahh the wonderful M27X balance shaft issue. I haven't had one in awhile so I'm probably due to get one. It's kinda like playing russian roulette when you get a m272/3 engined vehicle with the check engine light on. You have to ask yourself, "Do I feel lucky today?" and hope that the fault code turns out to be for just one of the cam adjuster solenoids and not the the fault codes-o-death, 1200 and 1208, indicating constant adjustment.

Anyways for anyone wondering the vehicles I've seen come through needing this have been mostly 2006-7 models but not limited to that as MBDOC said. ML350, R350, C230, S550, GL450 just to name a few. My experience has been limited to 2 GL450's and one ML350.

I've got two at my shop right now, an ML and an R Class. It looks like two of my guys will be busy for the next few days. :D They're both out of warranty, but I'm sure MB will help out.