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#1
03-06-2010, 01:41 PM
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Interesting cam/chain failure
A buddy mine towed his car over to me. His 300SD quit while doing low speed around town driving. Pulled the valve cover off and this is what I saw. I have seen cam failures but I think this one is a bit different. It looks like the rocker retainer came off, then the rocker slid on the shaft and locked the cam. You can see the cam snapped near the center the the front cam towers are broken. I don't think those towers broke due to the pistons smacking the valves. What it looks like to me:
Cam got locked, and as the cam twisted I think the chain was strong enough to where it actually ripped the towers upwards until the chain and cam snapped. You can see the left side of the towers are higher than the right like it was lifting/rotating. What will be interesting to see when I get the head off is whether there was valve/piston contact or if the lifting of the towers prevented the rockers from actuating the valves.
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Last edited by vwkess; 03-08-2010 at 10:17 AM. 
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#2
03-06-2010, 01:43 PM
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A shame as this was a very well maintained one since new... look how clean that valvetrain is!
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#3
03-06-2010, 02:08 PM
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What year is the car? There was a recall on some early 617's for cam problems. Can't remember the exact details.
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1977 300d 70k--sold 08 1985 300TD 185k+ 1984 307d 126k--sold 8/03 1985 409d 65k--sold 06 1984 300SD 315k--daughter's car 1979 300SD 122k--sold 2/11 1999 Fuso FG Expedition Camper 1993 GMC Sierra 6.5 TD 4x4 1982 Bluebird Wanderlodge CAT 3208--Sold 2/13
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#4
03-06-2010, 02:12 PM
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It is an '84.
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Last edited by vwkess; 03-08-2010 at 10:17 AM.
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#5
03-07-2010, 08:32 AM
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BTW, last service he did was a valve adjustment about 5k miles ago. I wonder if the retaining spring wasn't accidentally knocked loose during this. Something to double check!
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#7
03-07-2010, 08:51 PM
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I have seen very similar damage from broken chains, but not the same. I have never seen a broken chain cause a rocker to walk off the shaft like that and lock itself against the cam tower.
 The chain was replaced 40k miles ago; it did not break at the master link.At any rate, I pulled the head off and there is no valve or piston damage... no contact was made on any of the cylinders. Looks like when the towers did break it lifted the cam enough that the valves weren't actuated. Lucky!! I think when he did the last valve adjustment he accidentally knocked that retaining spring loose when installing the valve cover. I know that is something I will be more careful with in the future too! So it is off to a storage unit for now until my buddy figures out what he wants to do. Maybe I'll end up picking it up 
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Last edited by vwkess; 03-08-2010 at 10:19 AM.
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