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  #1  
Old 04-23-2010, 11:42 AM
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Need opinions on possible engine damage.

All I wanted to do was stop an oil leak on my 1994, S350 TD (213,000 miles). I took the car to a non-dealer but experienced Mercedes mechanic. The "bad head gasket" was quickly identified as a cracked head (a well known design flaw in this engine). I had the mechanic check for bent rods and cylinder wear. Everything checked out fine. I said go ahead and replace the head.

Several weeks later I get the car back. It went 70 miles before "blowing up". The #1 intake valve dropped into the cylinder and broke up. Parts blew back into the intake manifold and went through the #5 cylinder. Obviously, major damage.

The mechanic rebuilds the engine on his dime (of course). Several weeks later I pick up the car. It goes 550 miles and blows up. This time it looks like the #3 cylinder had a valve being struck by the piston. The engine had a ticking sound like a bad lash adjuster, but it was not loud. Anyway, the disk/puck that the cam pushes against shattered, the cam broke, at least one cam journal mount broke, and that's what was apparent with just the valve cover off.

My question is, doesn't all this trauma to the engine have a high probability of causing unseen damage to things like the crankshaft, main bearings, rods, and anything else that's an internal part of the engine?

Also, the new head was setup by a shop that specializes in diesel engine work. On the first failure, they claimed the valve dropped because a "spin" weld on the valve stem just below the point where the valve keepers engage the stem, failed (act of God, not their fault). Anyone got an opinion on that?

The same shop assembled the second head. They haven't responded yet to the latest failure.

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  #2  
Old 04-23-2010, 11:48 AM
rrgrassi's Avatar
mmmmmm Diesel...
 
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"Act of God", yeah right. Poor workmanship is what it sounds like to me. the "Act of God" claim could be feasable if the engine was damaged by a weather or geographical event. Valve stem failure would be caused by poor manufacturing, or an "Act of MAn"

Sounds like they did not check and double check everything.
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70's Southern Pacific #5608 Fairmont A-4 MOW car

13 VW JSW 2.0 TDI 193K, Tuned with DPF and EGR Delete.

91 W124 300D Turbo replaced, Pressure W/G actuator installed. 210K

90 Dodge D250 5.9 Cummins/5 speed. 400K
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  #3  
Old 04-23-2010, 12:06 PM
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I'm with RRGrassi on this one. They were supposed to identify the problem and fix it. blowing up 550 miles later is too close to be a coincidence in my book.
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  #4  
Old 04-23-2010, 12:32 PM
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What an unfortunate sequence of events to happen. It also sounds like it is going to take quite an effort to get this all sorted out. Hope it all goes well.

At least there was no direct intent to mess things up. Other posters are right thought that an act of god does not quite cut it. Things can go wrong unintentionally. Thats why insurance exists.

Residual damage is also an interesting posssibility as you mentioned. There is not much happiness in an event like this. There now probably is enough money involved to need someones insurance company inputs unfortunatly. The safest action on their part would be to replace the long block with an exchange rebuilt. At todays costs they may be able and attempt to write the car off.

By the way this may be an opportunity to install the almost bulletproof 3 litre lower block in comparison to the 3.5 litre as well. In my opinion any opportunity to do that is very worthwile in my opinion. This whole situation just might have an upside. That does not in any way mitigate the stress of the event at this point much of course.
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  #5  
Old 04-23-2010, 12:35 PM
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While part do fail it actually sounds like the Camshaft Timing was slightly of allowing some contact with the Valves.
There is also a possible that the first Time one of the Valve Keepers was not in good and came loose.

Also the Valves are only allowed to protrude a certain amout from the cylinder head.

Speaking in general with a Cylinder head is re-surfaced and the Valve Seats are reground. The Valve Stems will be taller (height) in relation to the inside top Deck of the head. The Hydraulic Valve Lifters can only compensate for a certain amount of Valve Stem Height.
To correct this on other Engines you grind the end of the Valve Stem to make it shorter.
Or in some American Engines they have shorter Pushrods you can buy.
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  #6  
Old 04-23-2010, 12:43 PM
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Quote:
Originally Posted by Diesel911 View Post
While part do fail it actually sounds like the Camshaft Timing was slightly of allowing some contact with the Valves.
There is also a possible that the first Time one of the Valve Keepers was not in good and came loose.

Also the Valves are only allowed to protrude a certain amout from the cylinder head.

Speaking in general with a Cylinder head is re-surfaced and the Valve Seats are reground. The Valve Stems will be taller (height) in relation to the inside top Deck of the head. The Hydraulic Valve Lifters can only compensate for a certain amount of Valve Stem Height.
To correct this on other Engines you grind the end of the Valve Stem to make it shorter.
Or in some American Engines they have shorter Pushrods you can buy.
Good point, the head should be measured to see if they took too large a cut if the head was resurfaced. I think very little is allowed as most members know.

There may have been direct involvement both times if it was over done. This is just a thought. Only measuring would verify it. It is the heads rebuilders responsibility to check a used head for deck clearance allowance.Before resurfacing. I suspect they just may have taken too much material off it themselves to true it up. Just a possibility. In no way a certainty.
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  #7  
Old 04-23-2010, 01:22 PM
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As to your question: I would be concerned about the rods that were associated with any piston that was involved or hitting valves. I don't think I would worry about the bottom end unless debris somehow got into the oil system and circulated.
As to your issue: Sounds like the machine shop shaved the head too much, the head was installed with improper valve timing or the valve length (as mentioned prior) was improper for the setup. Inertia-welded valves have been in use for many years and while they do fail at the union of the two parts, it's almost always the result of an impact with the piston. Also, IIRC, the union is close to the head of the valve and not, as the shop stated, below the valve spring keeper grooves. Unless the MB valves are constructed totally differently than the domestic stuff I'm familiar with.
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  #8  
Old 04-23-2010, 01:33 PM
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To the best of my knowledge, the cracked head "well known design flaw" was corrected long before the 1994 model year. I bring this up to question the experience of the mechanic, if it is not accurate (comments?).
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  #9  
Old 04-23-2010, 03:26 PM
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The mechanic is supposed to check the quality of the machine shop's work. Perhaps they will buy & install a crate engine of your choosing.
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  #10  
Old 04-23-2010, 03:28 PM
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Eitherway, this is thier responsibility to fix, and get fixed correctly.
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70's Southern Pacific #5608 Fairmont A-4 MOW car

13 VW JSW 2.0 TDI 193K, Tuned with DPF and EGR Delete.

91 W124 300D Turbo replaced, Pressure W/G actuator installed. 210K

90 Dodge D250 5.9 Cummins/5 speed. 400K
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  #11  
Old 04-23-2010, 03:36 PM
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My guess is shaved too much material off head, raised compression as well as chance of collision, with any slop in the chain / tensioner. Let me guess, no new chain went on?
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  #12  
Old 04-23-2010, 04:07 PM
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Actually, I asked that a new timing chain be installed. The mechanic installed it at his own expense. A nice gesture.
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  #13  
Old 04-23-2010, 04:46 PM
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Something is certainly amiss. Would seem to me that the mechanic? and the machine shop need to be buying and installing and warranting a new motor for you.

At this point Id opt for them buying the new motor and having someone who knows what they are doing install it.
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  #14  
Old 04-23-2010, 07:50 PM
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IF, they agree to take financial responsibility, they will likely reference the value of the car, and consider it totaled / offer to buy you out as that is cheaper than a good reman engine. Good luck.
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  #15  
Old 04-23-2010, 08:26 PM
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What a sad sequence of events. My sympathies. To my knowledge, God does not work on diesel engines. His time is mainly taken up with earthquakes, tornadoes, volcanoes, impregnating virgins and helping football teams.

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