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  #1  
Old 11-09-2007, 11:59 AM
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86 560SEL what happened?? :(

My 86 560SEL w/ 64K miles was running smooth as silk. Was sitting or a few days. Went out to drive it, started it up and it sounded terrible. Made loud knocking sounds but ran smooth, oil pressure gauge all the way up at 3 bars. I turned it off and now it won't even turn over!! Turn the key, everything lights up, turn key to start and just a hear a clunk. I've had a little trouble with the neutral safety switch, but could always jiggle the shifter and get it to start.

I'm worried the engine locked up from the terrible clunking sounds when I started it before.

Haven't gotten it to a mechanic yet. Obviously will need towed.

How could an engine that was so smooth and quiet just all of a sudden make such knocking sounds?

Could it be something simple or should prepare for the worst?
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  #2  
Old 11-09-2007, 12:29 PM
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Sounds like the timing chain ate a plastic rail guide and then the chain jumped out of time and the valves hit the pistons. A standard way of failure for these engines. Expensive to fix at this point.
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  #3  
Old 11-09-2007, 01:24 PM
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If that were the case, would it still run? The car started up fine and I let it run for a couple minutes. It didn't run rough, just made a loud knocking sound. Engine wasn't shaking or anything like that.
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  #4  
Old 11-11-2007, 03:36 PM
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Quote:
Originally Posted by dpetryk View Post
Sounds like the timing chain ate a plastic rail guide and then the chain jumped out of time and the valves hit the pistons. A standard way of failure for these engines. Expensive to fix at this point.
That was my first thought also, the plastic rail guide disintegrated or broke.

It ought not to have happened at just 64,000 miles, but then 21 years without having had it changed is a LOOOOOONG time on the original one.

Mileage and time causes the original ones which are white, to become root beer brown, and over time and mileage they develop hairline or big cracks, and eventually they let go. There is no set way to tell, on the 560, it varies engine to engine, but the best bet is to change them along with the chain and tensioner at 100,000 miles (typically driven in 10-12 years)
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  #5  
Old 11-14-2007, 01:25 AM
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Yikes
My mechanic says wait for the rattle

Not feeling very comfortable here...

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  #6  
Old 11-14-2007, 09:39 AM
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If you "wait for the rattle" you are really taking a chance...many times "the rattle" is the first and last thing you will hear as the chain jumps time and the carnage begins inside the engine. 10 years and/or 100K miles...when you hit those numbers it is time for a new chain, tensioner, guides, etc.
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  #7  
Old 11-27-2007, 01:46 AM
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91 420SEL LH Cam jumped time, bent exhaust valves. What's the cause?

I bought a 91 420SEL a few years back and gave it to my son to use while he was going to law school. It had 200,000 miles on it and the timing chain had never been replaced so I order the parts and was waiting to take it into an independent shop to effect the change.

Before it was done, the car was driven by my wife (a school teacher, no less) and she returned it to the garage. It sat for a couple of days before I tried to start it and it wouldn't. It turned out that the LH exhaust valves bent on the startup attempt and it seemed to conform to that described elsewhere in this thread. I pulled both valve covers and found the inner upper chain guide on the LH side broken and the exhaust valve rockers out of contact with the cam. There was no damage to the RH side.

The timing chain, tensioner and upper guide rails were replaced and the LH head reworked by an independent shop. The car ran perfectly for 15,000 miles. Then it failed to start when my son ran into a bank for 15 minutes. After it was towed to a local MBenz dealer, the failure was determined to be the ignition control module (by substitution) and it was replaced with a used one from eBay.

Two weeks later the 420 failed again while running. The failure occurred while running at moderate acceleration (34-40mph) with the engine warm. A clunk was hear, the engine began to lose power and it stopped completely and would not start. This time, I had it towed to my home. After checking the obvious, I pulled the LH valve cover and found the exhaust valves not returning with the rockers dropped off for the exhaust valves. I also saw a small chard of plastic (about 3/8" polygon) on the ledge of the chain cavity and took a picture of it.

Could one of the new guides have fractured? Or, could a piece of the old guide rail been left in the engine? With a mirror and light, I could see no evidence of any missing parts or damage to the new upper chain guides. I called the independent shop, got sympathy, but no plausible explanation of what could have happened.

Over Thanksgiving weekend, I disassembled the top end of the engine. The timing chain guides were indeed intact, the timing chain was still in mesh. I turned the engine to TDC using a socket on the crank. The RH cam was in time, but the LH was off, late about 12-15 degrees (the tower mark on the left cam tower is somewhat ambiguous). The LH cam had indeed jumped time as suspected. I checked the distributor rotor position as well and it was in time.

Why? I removed all three plastic rails. They were in perfect condition. I removed the hydraulic tensioner and rail. The plastic tensioning rail, too, was in perfect condition. In fact, everything that had been renewed a year and a half earlier was in perfect condition and installed properly. I removed the LH head to have a valve job done on it. But, the problem of why it occurred keeps nagging me and I began to remember the admonition of the definition of insanity. So I went to this website.

I've read the speculative posts, most of which don't make sense to me. The lack of oil pressure on start up doesn't apply here because it failed the 2nd time while the engine was running. Besides, what engine designer in his right mind would rely on holding hydraulic pressure through a check valve for extended periods to avoid catastrophic engine (interference) damage? Too, the tensioner is preloaded with a mechanical spring and this failure wasn't at start up, but at moderate running speed. (I noted that Mercedes has increased the mechanical tension on the replacement hydraulic tensioner such that a longer bolt has to be temporarily used to draw it up). Worn sprockets? No evidence at all. Brand name disloyalty which should be punished? No, replacement tensioner supposedly was Mercedes; likewise for chain and plastic upper guides. Low oil? No, it was recently changed and was less than a half-quart low. Failure of the oil pump? Could be, but it would most likely be catastrophic, not intermittent; dropping the pan shows no apparent problem with the pump or the oil pump chain.

Improper repair? Well, there was some evidence of some minor things done poorly like two o-rings in an injector holder due to improperly cleaning the old one out of the cavity, but nothing material to the fault of jumping time. The car passed emission tests shortly after the first repair and subsequently without problems. However, I don't know that the engine was in perfect time after the repair, but I doubt that it was marginal.

This timing chain problem with the 420/560 discussed herein has far too many instances for anyone to have found the true cause and it seems endemic to this engine design. (I have a 76 MBenz that has over a million miles with the same time chain; likewise a 300TD with 375K miles with the same timing chain and I have never had a GM engine timing chain fail. Replacing a double-row steel timing chain every 100,000 miles as preventive care sounds ludicrous, because it is. Speculation about oil check valves preventing chain slap on start up may be true, but if it is so, the engine designer should be shot. I suspect something else is going on that preconditions this engine for timing failure on startup or while running. At least in the instant case, I know it is not "chain stretch" or "broken chain guides" or "worn sprockets" or the other transplant diagnostic, whip-the-messenger-boy catchalls.

As coach Bear Bryant remarked, there's just too many failures on this side of the field.

Why just the LH side? It's the first in the series, for sure. But if it were due to a worn crankshaft sprocket (which has one half the diameter sprocket of the cams, thus less teeth in contact, and would be the first sprocket to encounter a slack loop upon failure of they hydraulic tensioner), all three (LH cam, RH cam and distributor) would slip time - not just the LH side. There was no evidence of bearing seizure on the LH cam or towers and the cam turned freely as it should.

Now, I have no reason to advance this new conjecture other than that the others fail to satisfy the instant case fault phenomenon, but here goes: What if the so-called timing chain/guide "failure" was a symptom rather than a cause? No post that I have seen in the past two or three years offers anything but speculation about how this failure actually occurs. I did see some pictures on one site whereby a reconstruction of the broken guide could run under the LH cam and act like a broom handle in a bicycle chain. But has anyone been able to reconstruct simulation of this catastrophic failure?

The theory that a piece of a broken rail is carried up over the top of LH sprocket works against gravity since it would be on the inside, not the outside, of the chain. The break of the tip of the LH inner chain guide is plausible, but such was surely not the instant case. Besides, this instance does not have any damage to the upper LH guides, inner or outer. So how did it slip time on the LH side and leave the intermediate mechanism of the failure intact?

I've looked into the dynamics of chain design and it may be ignition related. The load on the chain varies (pulsates) as it pushes down the valve springs and it reacts to change in load. I'd like to see a strobed picture of a chain running under load whereby the ignition is interrupted to see if failure could be simulated. (Bear in mind, the MB inline diesels, which use mechanical injection and have no immediate shutdown, don't have this problem, though they use the same type of hydraulic tensioner and chain. Sure, chain "stretch" will affect diesel valve and injection timing, but they don't have any where near the incidence of catastrophic "chain failure" of the 420/560 gas engines. Could it be that such an event as an abrupt ignition cut off creates a "traveling wave" that presents a whiplash loop that invites the first loaded cam to skip a tooth and/or also breaks the plastic guide rail (if it's embrittled with age)?

This engine ran for 200,000 miles on the original chain, so why did it fail with only 15,000 miles on renewed OEM parts? What could the repair shop have done wrong (or failed to do) that could have caused this second failure? What quantifiable specification was violated?

I'm going to take off the front cover and take photos while I'm doing it to see if I can forensically determine the cause, but would appreciate any insight those that have been there may have.
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  #8  
Old 11-14-2007, 12:45 PM
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Quote:
Originally Posted by CamelotShadow View Post
Yikes
My mechanic says wait for the rattle

Not feeling very comfortable here...

If money is an issue, yeah just wait for the rattle then you have to change it. It could last for a few more years.

If you have the money I'd do it right away, since chances are they are original...
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  #9  
Old 11-14-2007, 01:01 PM
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what about my 84 300SD w/ 210K and my 85 300SD w/ 240K? do they have the same issue?? are u saying i need to have them torn down to have the chain, tensioner and guides replaced as well?
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  #10  
Old 11-09-2007, 01:29 PM
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I think your going to find out that your 560 didn't have 64K on the clock. Have you tried turing the motor over by hand?
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  #11  
Old 11-09-2007, 08:26 PM
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It checked out with autocheck.com when I bought it with 53K. Also, service stickers and books would support the mileage represented.
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  #12  
Old 11-09-2007, 08:32 PM
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Did you inspect the engine for visible damage?

T- chain will sometimes knock a hole in the valve cover.

Perhaps an ancillary component failed- belt or pulley?
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  #13  
Old 11-09-2007, 10:52 PM
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Nothing appears amiss.
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  #14  
Old 11-10-2007, 10:57 AM
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here's an account of exactly what happened...

i got in the car, turned the key and started engine. shifted into reverse. HMMM... engine sounds different. shifted back into park. opened door. WTH?? sounds like a really bad valve tap but more clunky than that. opened the hood. car still running. everything looks ok. got back into the car. pressed gas to speed it up just a little, like maybe 2500rpm. still same sound. hmmmm... i better turn it off. turned engine off. tried to restart. turn key, just hear click. wiggle shifter cause i've had it not start a couple times cause it didn't seem to be in park correctly. just hear click. thought, oh f...

got into my trusty 85 300SD w/ 238K and went to office

560 sitting in the same place since then
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  #15  
Old 11-27-2007, 04:07 PM
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Quote:
I have a 76 MBenz that has over a million miles with the same time chain
What model?

Seems from reading these boards that for every m117 failure, there are 20 m116 (420) failures.

Never hear much about 450 or m100 t chain failures. or at least i don't.
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