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Old 01-09-2017, 02:59 AM
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M156 - Trashed Hydraulic Bucket

Found this bucket while disassembling an 2008 CL65 with a M156 motor... the engine was undergoing a renewal of camshafts and hydraulic buckets due to a pre-existing factory defects with the cams and buckets.

Obviously the bucket will be renewed but take a close look at the top of the valve stem that utilized this bucket... the head is rounded. Can this be used, as is, or does the cylinder head need to be pulled and the valve renewed?

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M156 - Trashed Hydraulic Bucket-dsc_4782.jpg   M156 - Trashed Hydraulic Bucket-dsc_4779.jpg  
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Old 01-09-2017, 07:57 AM
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It's done.
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Old 01-09-2017, 10:07 AM
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Location: Conway, SC
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Looks like it's time for a valve job.
Mercedes Benz Master Tech - Retired
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Old 01-09-2017, 06:18 PM
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It is hard to tell from the pic if the valve stem tip is concave or convex.

In any event, the wear looks like it is entering the top groove of the valve lock so there is a real risk the locks will fail.

What is the "pre-existing factory defects with the cams and buckets" ?

As to what caused the failure, I vote for that lash adjuster to have collapsed, engine run with a tapping valve and the fatigue broke the bucket through / hammered the valve tip. ( Remember, the lobe contacts the outer diameter of the bucket first leaving the center unsupported. )
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Old 01-10-2017, 02:14 AM
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The visible portion of the valve stem is convex in shape. If you look closely at the bore from which the faulty bucket resided you can see a small little "bump" just outside of the bucket's bore in the region of the curved machined surface. That "bump" is actually a small metal ball that served as a spring loaded oil check valve within the bucket. When the bucket self- destructed that ball was released and somehow was imbedded in the metal of the cylinder head.

Early M156 motors had problems with improperly hardened camshafts which resulted in accelerated lobe wear and faulty hydraulic bucket design that resulted in premature oil leakdown.

A M-B TSB is attached; M-B released redesigned buckets and camshafts but then there was the issue of the cylinder head bolts suffering from accelerated corrosion and failing prematurely. The M156 was a basket case of issues which makes owning an early version a risky proposition. There was an attempt at a class action suit several years ago, which apparently didn't go anywhere.
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File Type: pdf S-BN-05.20 20b - 23 Jan 09.pdf (325.7 KB, 152 views)
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Old 01-10-2017, 02:33 PM
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Join Date: Feb 2007
Location: los angeles
Posts: 707
Your lucky , i did a repair last year with the same issue, only it dropped the valves, which in turn destroyed the piston and block , broke chunks off the crank the bill was $27,000 , recommend you replace all lifters , pull that head replace the 1 valve , replace cam , all buckets

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