SLK/R171: Broken valve spring.
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2005 350 SLK
Broken valve spring.
I recently bought a 2005 350 SLK with 123 000 km on the clock. I normally refrain from purchasing vehicles with more than 100 000 km, but heard from friends that these are reliable cars and the engines can do 500 000km without being opened. After doing another 4 000 km however, it left my wife stranded next to the road with a total loss of compression on one cylinder. After dismantling the engine it was found that a valve spring had broken. The total cost of repair is in the order of ZAR 50 000. I am now utterly disgusted with the reliability of these engines, as I ownwed a few other Mercs in the past without any engine problems. Can someone tell me if this is a common trait with the 350 V6 engines, or was the valve spring inferior in the first place?
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2010 SLK350
I've not heard of this issue either - on any m272 motor from any chassis.
That said, the 2005 SLK350, being the introductory year for the m272, is rather susceptible to odd ball problems like this, stuff that MB probably knew about, and revised in one of the ten dozen revisions that have been made to that motor over the years.
Just for archival sake for the thread and forum --- the valve spring that is specific for the 2009-2011 SLK350 ONLY, is approx 20lbs stiffer than any of its predecessors. This was done in order to handle the increased rev limit of the m272.969 in those 3 years of the SLK350. So, if someone had to change valve springs - I highly recommend purchasing them for the 272.969 version of the motor. You'll need new valve seat retainers as well, considering the spring is also conical in shape, versus cylindrical. The base is wider in diameter. All the other related parts are fine replacing as-is as needed.
That said, the 2005 SLK350, being the introductory year for the m272, is rather susceptible to odd ball problems like this, stuff that MB probably knew about, and revised in one of the ten dozen revisions that have been made to that motor over the years.
Just for archival sake for the thread and forum --- the valve spring that is specific for the 2009-2011 SLK350 ONLY, is approx 20lbs stiffer than any of its predecessors. This was done in order to handle the increased rev limit of the m272.969 in those 3 years of the SLK350. So, if someone had to change valve springs - I highly recommend purchasing them for the 272.969 version of the motor. You'll need new valve seat retainers as well, considering the spring is also conical in shape, versus cylindrical. The base is wider in diameter. All the other related parts are fine replacing as-is as needed.
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2010 SLK350
Here is a picture I snapped of regular m272 (272.960-67) valve spring versus the 272.969 valvespring found in the 300+hp 7200rpm 09-11 SLK350.
Tested @ 20lbs stiffer, and as I already mentioned - conical design w/ larger seat.
Tested @ 20lbs stiffer, and as I already mentioned - conical design w/ larger seat.
Last edited by RedStripe; Apr 22, 2012 at 11:32 AM.
