Broken valve spring.

joslowe · 10-13-2011, 02:15 AM

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?

To remove this ad, register today or login if you already are registered!

Johnsct · 03-07-2012, 11:10 PM

In all my research for R171 350's, I haven't seen this problem. It doesn't seem to be a common issue. Sorry it's happened to you.

roadtalontsi · 03-12-2012, 01:06 AM

ive never heard of or seen a broken valve spring on a 272 or 273 motor, balance shaft or chain idler pulley - ya.

RedStripe · 04-22-2012, 12:21 AM

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.

RedStripe · 04-22-2012, 02:15 AM

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.

04-22-2012, 02:15 AM	#5
RedStripe Banned Garage is empty, add now Join Date: May 2011 Posts: 182 Drives: 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. Attached Thumbnails Last edited by RedStripe; 04-22-2012 at 11:32 AM.

Thread Tools	Search this Thread
Show Printable Version Email this Page	Search this Thread: Advanced Search
Display Modes	Rate This Thread
Linear Mode Switch to Hybrid Mode Switch to Threaded Mode	Rate This Thread:

03-07-2012, 11:10 PM	#2
Johnsct Member Garage is empty, add now Join Date: Jun 2007 Posts: 91 Drives: 2006 SLK280	In all my research for R171 350's, I haven't seen this problem. It doesn't seem to be a common issue. Sorry it's happened to you.

03-12-2012, 01:06 AM	#3
roadtalontsi Member Garage is empty, add now Join Date: Oct 2007 Posts: 115 Drives: 93' turbo supra	ive never heard of or seen a broken valve spring on a 272 or 273 motor, balance shaft or chain idler pulley - ya.

04-22-2012, 12:21 AM	#4
RedStripe Banned Garage is empty, add now Join Date: May 2011 Posts: 182 Drives: 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.

Currently Active Users Viewing This Thread: 1 (0 members and 1 guests)