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Balance Shaft Sprocket

41K views 54 replies 24 participants last post by  jbanks15 
#1 ·
Hi All. I recently bought 2005 SLK350 privately in UK. All is good but have read about Balance Shaft Sprocket problems on this engine. Car has done 42,000 miles with full MB history. Should I be worried about this issue? Appreciate your comments. Stuart.
 
#2 ·
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#3 ·
Yes this is somewhat common on a certain range of 272 engines. However i can say from personal experience i've never seen an slk affected by this in the past 6yrs. It tends to be the heavier cars, not sure if its conicidence. I've personally done gl450, s550, e350, sl550, r350, ml350 but never a c-class or slk. the v-8 (273) has an idler pulley rather then a balance shaft. Usually if the car is in good shape and frequents the dealer for service they will good will the engine job. I've never done one customer pay, they've always been under warranty or goodwill. I've also never seen any engine damage occur from this. <- unless the technician is stupid. haha. I wouldnt worry too much about it.
 
#5 ·
My EML came on a couple of weeks ago, it has now been diagnosed as having a worn Intermediate shaft. I originally took it to a Mercedes Spec, who have let Merc look at it, to see if they agreed that this was the problem. They have now confirmed that this is the case and after two attempts at a warranty claim they have declined to do the work under warranty! Even though the car has full MB service history and only 42k!
 
#8 ·
No warranty on the car unfortunately. I took it to a Mercedes Specialist who gave the car to a Mercedes dealer to confirm their diagnosis. Once this was confirmed they contacted MB UK to see if they could cover it under warranty, this was refused on the first and second attempt. Car is on its way back to the Specialist who are going to carry the work out for me.

There was no warning, just driving to work and EML just came on!
 
#14 ·
OK, Just had a phone call from the Indie doing the work. Job is now done. I am yet to collect the car... will not be until Tuesday as I am away at the moment, however he did say that there seemed to be aprox 3-4 teeth missing from the balance shaft gear. They also said that the shaft its self it very worn!

Once I have collected the car I will let you know if there are any audiable differences.
 
#15 ·
Balance shaft sproket problem M272 engine numbers affected

I am interested in this problem because it is an interesting metallurgy failure -rather like the piston ring problem on 2005 SLK350's.I am hoping others will chime in to correct/add to what I found.
You can find lots of info if you google "M272 balance shaft failure" .It will also give info on a Class Action suit related to this. Interesting that the V8 M273 engine which has the same sprocket but not the balance shaft(V8's are inherently well balanced unlike our wobbly 90 degree V6).

The symptoms of this sprocket problem are initially "valve train clatter" .Eventually a MIL code is set- 1208 or 1210.Sometimes the problem is misdiagnosed and the culprit is the purge valve chattering.

The best source I found was:
MB DTB S-B-03.03/08i dated October 24 2008. -lots of tech details and photos.
Repair kit part number is :repair kit is A2720300013 w/o replacement of oil pump.Repair involves more than simply replacing one sprocket!
Repair takes over 30 hours because engine needs to be removed and front of engine stripped.

The cause was 'soft metal' (actually a failure to correctly heat treat powdered metal) being used for "SOME of" the balance shaft sprocket on earlier M272 engines.
M276 engines do not have the balance shaft because they are inherently balanced 60 degree v6 (not unbalanced 90 degree V6 like M272)

The problem can affect all M272 enginesup to engine number :(272.942) 30468993. The last 8 digits are what matter .Those I put in parenthesis merely identify the engine type/application.This means if you have an '07 or earlier,you'd better check your engine number.The number is on the front of the left cam cover but is difficult to find read. Your MB dealer can tell you the engine number from your VIN.
Although there are some press reports of goodwill repairs,most enthusiast forum contributors dispute that.
Mercedes Hit With Timing Chain Issues on 2004-2006 V6 and V8 Models | The Truth About Cars

Mercedes seem to have been late to learn the lessons of GM's ill-fated 90 degree V6 engines(according to some).Such sources would cite the change to 60 degrees for the current V6(M276) which is a chrysler developed design:
"Mercedes did something absolutely masterful, and only those who pay close attention realize that something changed from the 90 degree M272 V6 to the 60 degree M276 V6. The M276 V6 is Pentastar derived and other than the fact that the V angle changed which MB does document they make no mention of the change, and in fact to most it appears to be a direct injection version of the previous V6. "

BMW are planning a new 90 degree V6?
The Spun Bearing: The Case For the 90 Degree V6 (With Reservations)

I hope others will correct factual errors and add to the information to help those with balance shaft sprocket failure.
 
#33 ·
M276 engines do not have the balance shaft because they are inherently balanced 60 degree v6 (not unbalanced 90 degree V6 like M272)

Mercedes seem to have been late to learn the lessons of GM's ill-fated 90 degree V6 engines(according to some).Such sources would cite the change to 60 degrees for the current V6(M276) which is a Chrysler developed design:

"Mercedes did something absolutely masterful, and only those who pay close attention realize that something changed from the 90 degree M272 V6 to the 60 degree M276 V6. The M276 V6 is Pentastar derived and other than the fact that the V angle changed which MB does document they make no mention of the change, and in fact to most it appears to be a direct injection version of the previous V6. "
The only V6 engines that are "inherently" balanced are a flat 6 (Porsche) or a straight 6 (BMW). A 60 or 90 degree angle bank will require balance shafts or other measures to compensate for the harmonic engine vibrations. However, it is true that the 60 degree V6 is mechanically easier to balance that the 90 degree, the 90 degree V6 can and is made just as smooth in the case of the Mercedes, through engineering.

A 60 degree bank fits more easily in an engine compartment that the 90, and the engineering is less involved for smoothness. The only problem is the engine is taller. The higher hood line in the 3rd generations allowed the use of the 60 engine.

Why the higher hood line? Styling? Pedestrian safety? Oh and the Buick V6? Give me a break. Isn't that the company that went bankrupt and couldn't design an ignition switch that would stay on!:frown:
 
#16 ·
Well, our 2005 350 SLK 66,000 mi. is undergoing the balance shaft replacement as I speak. The initial replacement went smoothly, no warranty coverage all on me. But then the computer wouldn't reset. Now I find out the MB kit that that they have developed for this "hardly ever" problem had un matched sensors. Fortunately on the front of the engine so it doesn't have to come out again. So MB is sending new ones and the car sits.
 
#19 ·
Now I find out the MB kit that that they have developed for this "hardly ever" problem had un matched sensors. Fortunately on the front of the engine so it doesn't have to come out again. So MB is sending new ones and the car sits.
My mechanic pointed out to me that my sprocket has not been fixed because I still had the original sensors. This may be of interest for people who bought their vehicles second-hand and are wondering if their sprockets have been replaced yet. The sensors are easily viewable from the engine bay.
 
#18 ·
I never heard any valve train noise prior to my balance shaft replacement.

That's an interesting note on the sensors -- two of mine didn't work afterwards either, I wonder why. My self-diagnosis involving these sensors says they're more than simple hall-effect sensors.

I did read somewhere that the ME somehow knows the position of the engine at startup, prior to rotation. I wonder if these sensors provide that.

They surely are more expensive than your typical hall sensor.
 
G
#20 ·
I am seriously considering a 2006 SLK350 with 36k miles - engine # 272963 30 220877
When I see the car again, where are the sensors located on the block or heads?
Is there a picture or a thread that provide additional info?
Thanks.
 
#21 ·
They're on the heads -- facing the front. Sorry I don't have any pictures. There are larger actuators with three bolts each, and smaller sensors are held in by a single bolt each. It's pretty easy to see the sensors, but seeing the part numbers will be difficult. They're pretty easy to remove, especially the intakes. From my experience, disconnecting these sensors will likely cause a code the next time you restart; once cleared it will go away permanently.
 
G
#23 ·
M272 balance shaft sprocket wear

Thanks to all for the info and help - I have now done extensive search about this problem and discovered a class action lawsuit filed in NJ about two years ago against MB for not owning up to a defective part. An MB service bulletin was also issued.
Engine SNs for this potentially "soft metal" sprocket included the 2006 SLK that I have considered purchasing, so I'm probably backing out, even though nothing was shown on the AutoCheck report for service. Would CarFax have been more accurate??
:(
 
#29 · (Edited)

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#30 ·
I wouldn't dismiss a car merely because it's in the range. While the issue is a major one if it occurs, only a small proportion of cars ever had the problem. My car, an '06, is in the range too. The more mileage on the car, the less likely it is to have the problem. A one-owner car with 36k on it might be considered more at risk than one with 89k, as mine was when I bought it last year, because this issue manifested itself earlier rather than later. None of the pre-purchase evaluation services will catch this; it will only show that a service was done at a particular time and mileage. And picky owners may have the car in frequently during the warranty period for various niggles; a lot of service visits shown is not in itself an indicator of major mechanical problems. If you like the car, buy it and negotiate extra warranty coverage for this specific issue if you can.
 
#31 ·
The sprocket issue is much like being genetically predisposed to having a certain illness.

While there is a small chance that you will be ill chances are you will not. It is no reason to avoid doing certain things or to live your life as you want.

Enjoy your car for what it is, maintain it the best you can, and if you are genuinely concerned about this issue (as unlikely as it is) then budget in anticipation for it.
 
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