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  #1  
Old 12-29-2003, 12:49 PM
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Timing chain on a 420 SEL

Hello friends,
I recently bought a very nice MB 420 SEL which had only 87K. It's in mint condition. I have 90K miles on it now. My major concern is replacing the timing chain. As many people say, I don't get a clacking noise when I change the oil. However, when I start it in sub zero temperatures, I do hear a clacking noise upon start for about 2-3 seconds. Is that noise coming from head lifters due to not getting oil at startup or the Timing chain slapping? Please advice.

Thanks
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  #2  
Old 12-29-2003, 04:43 PM
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usually the timing chain tensioner will cause this. Pull the covers check your guides cause you may as well do them and the chain at 100000
m
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Martin Ingram
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2005 320 CDI
2006.5 VW Jetta TDI
1991 560SEL (179000 Sold)
1972 280SEL 4.5 ('The Lead Sled' 320000 miles when sold.)
1972 220D (225000 when sold)
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  #3  
Old 12-29-2003, 05:36 PM
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hello

when cold outside mine also does this as with any oil it tends to thicken up when cold. if the noise disappears in a few seconds you're likely just fine. kinda watch your oil pressure gage when it shoots up it should quit in a second or 2. this i feel would be normal.

just a note on the chain. the rails, oil tubes and tensioner is a must somewhere over 100k but that doesn't mean the chain is no good. you can use offset keys to re-establish zero on the balancer for timing. one of our resident experts came up with a formula on his chain and plans on running it to 200k. but if you're doing the work the chain is only about 70$ and maybe an hour or so to replace.

if your car has had good maintenance you could see it go 140 or 150. of course some have broke at the mileage you've got now.

good luck
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  #4  
Old 12-29-2003, 07:54 PM
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I disagree, the tensioner should always hold pressure if it does not replace it. Temps here in CO are in the low single digits and my tensioner never does that. No matter how cold the tensioner must maintain pressure. The sound is chain slap. If the rails and chain are okay and the timing is not to far off then just put in a new tensioner. Your call, but fix the chain slap it will also increase wear on the chain guides.
m
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Martin Ingram
Colorado Springs
2005 320 CDI
2006.5 VW Jetta TDI
1991 560SEL (179000 Sold)
1972 280SEL 4.5 ('The Lead Sled' 320000 miles when sold.)
1972 220D (225000 when sold)
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  #5  
Old 12-29-2003, 08:08 PM
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I take it the 420SEL in question is a 1986-1991 W126 version. Forget the mileage. That car is at least 13 years old. The M116 engine has plastic timing chain guides that wear with AGE and mileage. Ignore the odometer and get into top end a little and check the plastic guides. If discoloured, replace the chain, the tensioner, and the guides. Disaster has befallen many M116 owners that did not pay close attention to this known trouble spot. The guides become brittle and break off. They jam the chain and often ruin at least one bank, potentially both.

Price out an M116 rebuild versus chain and guide replacement. Pay a little now or a lot later...
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  #6  
Old 12-29-2003, 10:20 PM
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Join Date: May 2003
Location: Rockville, MD
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Just Do It

I've got an 87 420SEL with 107K on it. Had put off doing the chain and guides for longer than I felt comfortable and finally had them done two weeks ago as my mechanic (Mitch Carr's in MD) said that they recommend 10 years or 100K as they were seeing too many guides break past 100K. My rails were dark brown and several had broken already but fortunately no pieces had dislodged -- they all had nice deep grooves etched into them. Mine was quiet as a mouse starting hot or cold. I agree with blackmercedes -- at minimum, get someone who knows to check it out. As I see it, when the alternative is $4K+ in valve damage (maybe more than the car is worth) getting it done in your mileage/age range seems to be money well spent.

John
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  #7  
Old 12-30-2003, 10:24 AM
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Thanks a lot for all the information guys.

John, how much did Mitch Carr charge you for the timing chain job? Also, does this job require an expert knowledge and experience with MB engines or can any good mechanic could do it? I also happen to live in Maryland.

Thanks
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  #8  
Old 12-30-2003, 11:14 AM
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Mitch Carr's said they usually do a 90/100K mile service with the chain if it hasn't been done and they quoted me ~$1200 for the chain and service combined. My tab was around $1300 but I did not need the extra service and had a bunch of other little things done instead. Runs like a top now. I'm not the one to ask if it requires special skill or not -- I only manage the most basic DIY jobs. I get the sense that it's not rocket science but there are some important pitfalls to avoid. That said, I really can't recommend Mitch Carr's highly enough. They have always been fair and honest with me. Check the Good Shops forum for more DC area shop recommendations or this thread:

http://www.peachparts.com/shopforum/showthread.php?threadid=3555&pagenumber=1

John
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  #9  
Old 12-30-2003, 11:48 AM
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Location: La Quinta, CA
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Cool

I paid $800 to have the chain, rails, and any related pieces replaced at an indie shop in California. Car was running fine but the parts were 16 years old. The plastic was discolored but had not broken. Car had frequent oil changes and all regular services since new.
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  #10  
Old 12-30-2003, 10:07 PM
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Location: LaPorte, IN
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As N ike says...

...just do it. I had the parts to do chain, upper rails and tensioner in my garage from 92,000 to 112,000 miles. Was too intimidated to attempt it. Until August 2nd. Appears that the tensioner didn't tension itself any longer, resulting in sloppy chain which broke the upper rails on the left. That event took out the lower left rail (found pieces of it in the oil pan and matched part number) and bent all 4 exhaust valves on the left side when she jumped timing. Because i didn't do what seemed hard, i ended up removing timing cover, do the heads, and the engine was salvaged by doing too much work and spending too much money when it was all avoidable!! Lessons learned:
1. There is too much first hand knowledge, both professional and experienced ametuer, on this forum to ignore. I listen closer now.
2. Old chain--virtually the same length as the new one. Thomaspin had alluded in some posts that chain stretch may not be the root cause of the problem--might have some merit.
3. Top rails get very brittle. Period. They can snap if something hits them (like the chain). Lower left rail broke from hard impact, but was not as crystalized as the uppers.
4. Chain tensioner--All right, this is my first time and i'm an insurance agent with no mechanical training, but in my opinion the tensioner seems vital to this equation. With no hydraulic pressure applied, the old tensioner was a whimp compared to the new. Is this what allows the chain to slap, breaking upper rails, jumping left cam timing, bending valves, breaking lower rails, runining engines or causing huge amounts of work when tensioner and rails at 100,000 and same plus chain at 200,000 would be much simpler???
5. I have now virtually torn down the top end of an engine and put it back together and it runs. Fairly well. That is a tribute to this forum and its members, and to MB's engineering. I would have destroyed any other engine by waiting too long, instead i got a great education.
6. Now that i've gone this far, i will not be intimidated by a difficult task again, in vehicles or in life. I know that avoiding the difficult will result in facing the near impossible.

Thanks for listening. In summary, change the rails and tensioner before i'm forced to come do it myself under cover of darkness!!
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  #11  
Old 12-31-2003, 07:49 AM
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You've got me scared

I have just purchased a 95S420 with 330k-kms (200k-miles+/-). Original owners service records do not show that the timing chain/guides have been touched. It probably is a ticking time bomb, but money being tight right now, I will address in the near future.

Has anyone compiled a list of parts necessary to do this job, like gaskets, bolts/nuts etc. I will probably replace the tensioner and water pump too!

Thanks in advance.
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  #12  
Old 12-31-2003, 08:43 AM
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Location: LaPorte, IN
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Don't know about your '95, but tensioner and rails can be done on the 126 420/560 for a few hundred in parts and fluids. Much of the parts list depends on the "while i'm in there i might as well..." feeling. This added cam oilers, valve stem seals, valve cover gasketsand several other odds and ends. A good study of the shop CD or alldata will help in looking at what is involved and what else makes sense "as long as you're there". FastLane Phil can help with parts determination as well. He's an execllent resource and the service can't be beaten. (I don't think i'd try to call him New Year's Day though!! )

This may not be as much an issue for your model as for the 126 v-8's, so do some searches on yours Tower.
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  #13  
Old 12-31-2003, 09:05 AM
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After fixin hundreds of failures, it is my conclusion that proper maintenance would be to replace the upper rails every 4-5 years or 50-75k. Do what you want with the chain and tentioner.

The problem in 90-100% of the cases is the fracturing of these rails with the pieces going between the gear and chain jumping teeth till it bends valves.

As to the tentioner, there is a check ball inside that retains the oil to maintain pressure. Even brand new tentioners can have that check ball leak occasionally and the short rattle that then occurs is what gets the rails. The rattle CAN NOT be permanently prevented. The ONLY prevention is to remove and replace the rails before they become brittle so they can do their job and contain the rattle when it happens.

Other than removing the pins, the rails are an easy DIY job, with gaskets it can't be more than $30 in parts. The rails are less than $5 a piece and there are three although the two in the left head are what cause most of the problems.

You can make the job more expensive but you will get little in return till maybe 175-200k.
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  #14  
Old 12-31-2003, 09:14 AM
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What are you guys doing up at this hour?

Thanks for your input stevebfl & greenacres.

Greenacres, you hit the nail on the head with the comment about a shop cd. I have the w124 cd for my 95E320, but I have been unable to locate a similar resource for the w140(?)-95S420. Lots of stuff to learn and digest as this high milage vehicle was obviously maintained but has standard wear items that the PO just didn't want to address near the trade-in date. Typcially dumb things like head rests not moving (done that on the E320 so presume is same), vibrations over 60mph (suspect tires...another couple hundred $), miscellaneous lightbulbs out on the dash, doors etc. (once I figure how to get the dash out and the door panels off, an easy fix).

Got the whole winter to experiment and hopefully not cause myself needless cost in breaking parts while attempting dissassembly.

Thanks again. If you know where I can get a copy of the shop cd for the w140, I'd greatly appreciate it.
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  #15  
Old 12-31-2003, 12:17 PM
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Re: You've got me scared

Quote:
Originally posted by tower
I have just purchased a 95S420 with 330k-kms (200k-miles+/-). Original owners service records do not show that the timing chain/guides have been touched. It probably is a ticking time bomb, but money being tight right now, I will address in the near future.

Has anyone compiled a list of parts necessary to do this job, like gaskets, bolts/nuts etc. I will probably replace the tensioner and water pump too!

Thanks in advance.
That is not an M116 engine. It's a 4.2L DOHC M119. Different engine. You should still look into the health of the timing system as it's got some miles on it now and the M119 chain is a long one that changes direction like all other V-8 chains.

At that mileage I would have the chain stretch checked right away and I might invest in a new chain and tensioner anyway. You probably got the car for a huge discount due to the mileage, and you'll need to invest some of that difference in the car.
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