W126 V8 Mercedes Timing Chain + Guide Install - Mercedes-Benz Forum
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post #1 of 42 (permalink) Old 01-15-2013, 10:03 PM Thread Starter
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W126 V8 Mercedes Timing Chain + Guide Install

In this write up I will be covering the timing chain install along with the upper guides. This is a relatively complex job so DYI'ers may want to really take their time. Use this information at your own risk. In other words, this is not an easy or quick job and will take several hours to complete. If you are not using special tools for this job an extra pair of hands will be needed.

FYI - If you are planning on just installing the upper timing chain guides you should check out this thread here -

Mercedes Benz 560 Engine Timing Chain Guide Replacement Photos - SL - SEC - SEL - Auto-Trend Repairs and Service Information Forums

The thread above will be more specific to just installing guides. It is important to remember that removal of the followers is not necessary if you just plan on replacing the guides, however if you are a rookie DIY'er it may be best to remove the followers to eliminate the possibility of re-coil on the passengers side camshaft when re-installing the chain and sprocket.

Now this thread picks up assuming you have already removed the valve covers, alternator, fan, belts, power steering pump and the spark plugs. I always start by installing the new guides prior to installing the chain because often times the old guides are very brittle if not broken when the job comes in. Installing the guides first ensures you do not have any of the old guides break or cause problems while rolling in the new chain.

The first step after all of the parts above have been removed is to take out all of the camshaft followers. To get information about how to remove the followers see this link-

Removing Camshaft Follower / Followers Mercedes-Benz 560 420 M117 M116 V8 SEL SEC SE SL - Auto-Trend Repairs and Service Information Forums

Once the followers have been removed as per the link above, you will then want to set the engine to TDC or "Top Dead Center". Do this by rotating the lower crankshaft pulley until the needle points to "0" (Zero) as shown in the photo below. This may or may not be TDC as the crank spins twice to every revolution of the cam.



In this photo above you can see the lower crank pulley is pointing to "0" (Zero). The next step to ensure the engine is at TDC is to either check the position of the distributor rotor (should be pointing to #1 cylinder)



Here you can see the hash mark in the center of the rotor matches that of the one on the distributor housing. I have marked the rotor with green paint for you to see, so it is not necessary for you to mark the rotor as the hash marks should be obvious. If the engine is 180 degrees off the rotor will be pointing in the opposite direction, simply turn the engine over one more revolution until its back at zero again and the rotor should be pointing to #1.





Now it's time to check your camshaft marks. The right and left camshaft will have markings like the one above. If the balancer is at Zero, and the distributor points to #1 then both left and right camshaft marks should align as shown in the photos above. If this is the case you are now at TDC. Remove the timing chain tensioner located on the right passengers side head held on by 13mm bolts. This will allow the slack needed for installation of the new guides.





I like to use a paint marker to mark my timing chain once the engine is at TDC. This helps to ease re-assiblily since it's often hard to see the marks on the back of the cam sprocket. It also helps to mark the "left" and "right" just incase. When finished we will use carb cleaner and a rag to remove the marks.
Now it is time to remove the center bolt on the left driver side camshaft sprocket. Using an impact really helps but if you don’t have one grab a pair of locking pliers and hold the camshaft (Not on the lobes!) while you bust it loose. With a rubber hammer tap on the back side of the camshaft sprocket until you can wiggle it off. Carefully remove the sprocket while keeping the chain taught. Use some mechanics wire to keep the chain up (do not let it fall in the engine) and out of the way. Now it is time to remove the outboard guide rail. Do this by removing the pins that hold it in.



In the photo above you can see a special tool being used to remove the timing chain guide rod pin. You can also make a home-brew tool out of your valve cover bolt, some washers and a small deep well socket. Remove both pins but be sure to be holding the rail so it does not slide into the engine.



Here you can see the left driver’s side outboard timing chain guide rail removed.



Here you can see the left outboard rails side by side New vs. Old. Note the color, as every time I see them break they are usually that off color orange. This suggest they have become brittle and are in need of replacement.



Here the left inboard rail has been installed. Be sure to use a sealant on the pins when re-installing to prevent oil leaks.



You can see in the photo above that both upper guides on the left cylinder head are in place and the pins have been installed and sealed.



And yet another look.



Here you can see Old vs. New on the left inboard rail, which just happens to be the same part number as the right hand side inboard (FYI).



And here is the backside of the left inboard guide. Now it's time to put the sprocket back on the chain and re-install. Do not fully tighten the sprocket bolt at this time, however run it down hand tight. This is when your little paint pen art comes in handy.



Here you can see the new inboard and outboard upper guides installed along with the sprocket. Your marks should be exactly where they were (TDC) if you did things right.
Now it's time to remove the right passenger’s side sprocket, doing pretty much the same as you did on the left driver’s side. Once the sprocket is removed and out of the way, with the chain held up with mechanics wire you will see the right side tensioner rail, which is shaped like a banana.



Above you can see the old tensioner guide. You remove it by taking out the 5mm plug on the timing cover and using a magnet to pull the pin while holding on to the guide. Sometimes the pin requires the use of an easy out to remove. Careful there is a washer on that plug you dont want to lose.



Here you can see the SERIOUS damage old brittle guides cause. This guide has worn clean thru and is now grinding on the aluminum shoe! This not good, and will now require us to remove the oil pan to fetch the chunks. While I often times see the left inboard guide kill these engines, it's quite clear the tensioner guides can be fatal as well if left too long.



In the photo above I have installed a new tensioner guide to the shoe. Look much better. Installation is basically the reverse of removal. Clean everything up nice.



In the photo above I have completed installing the timing chain tensioner guide, the right passenger’s side inboard guide and the chain and sprocket. Just like the other side everything should line right up and the engine should still be at TDC.
Now it's time to roll in the new timing chain. They make a tool for this, but to date I just have an extra pair of hands around and feed it by hand.



This is a factory OE chain, about the best you can buy. It also includes a master link, which if used properly is a safe way to link the chains. Be sure to buy TWO master links, the reason I will explain later. Also, I have seen on other forums people talking about soaking the chain, I am here to say that will make for a big mess along with hinder the installation of the chain. You can lube the chain AFTER it's installed. (FYI)



You must now decide what link to remove. I usually roll the chain in on the left drivers side sprocket, so that is where I remove my link. It's also important at this time to re-install the tensioner using a 4 inch bolt as to just barely take up the slack, yet not pull on the chain. This will prevent the chain from slipping. Once that is done be sure to get everything ready, such as the master link, the chain and a magnet. Remove a link by grinding the two pins flat. BE CAREFUL! You can get any shavings in the engine! You also can not drop any of the clips, links or anything else in the engine! Be sure to cover the area with rags when working with the links and clips but be sure to remove the rags when you are turning the engine.



In the photo above you can see me joining the new chain to the old chain using one of the new master links. BE VERY CAREFUL NOT TO DROP THE CLIPS IN THE ENGINE! KEEP A MAGNET HANDY! MOST IMPORTANT - NEVER RE-USE A MASTER LINK C-CLIP! THEY ARE ONLY GOOD FOR ONE USE! THIS IS WHY I SUGGEST GETTING TWO MASTER LINK KITS! One for rolling the chain in and one for final assembly.



In this photo I have the new chain linked to the old chain. I have the new chain lying across the engine. You only have to hook the chain up to ONE side. Your extra set of hands (helper) will be turning the engine clockwise (right) 1/4 turns at a time which will draw the new chain onto the sprocket. At the same time you must keep the other side taught as the old chain feeds out, you must also hold down on the sprocket as the new chain is feeding in to prevent it from slipping. It is a very complex action that must be done right without any screw ups! Your helpers arms will be tired, and your hands and arms will hurt afterwards. No margin for error here, however if this scares you they do sell a tool that makes errors less of an issue. I suggest going that route if you are a DYI guy as you may not be familiar enough with feeding the chain and end up costing yourself 5 times what the tool cost.



Here we have the new chain fed into the engine and the master link installed.



Here you can see the right passengers side cams are in the proper position.



Here you can see the left driver’s side cam is also in the TDC position. You should also have your balancer at "0" (Zero). If that is the case you now install your distributor ensuring the hash marks line up at the #1 position.



Here you can see the SECOND master link kit installed with fresh c-clips. You are now done with the timing chain and guides. Install your new tensioner and gasket now, and tighten your cam sprocket bolts. Then roll the engine over by hand 4 times. After doing so you should still be able to bring the engine to TDC with all the cam marks dead on with the balancer at zero. If this is the case congratulations! Put the engine back together and enjoy another 60-80K in worry free miles!

But wait! This one had a broken guide with chunks missing!



Don’t forget to clean out the pan if your guides are missing chunks! As you can see in the photo above, it's not pretty! Clean it up and all should be fine.

Last edited by 126; 01-15-2013 at 11:55 PM.
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post #2 of 42 (permalink) Old 01-15-2013, 10:39 PM
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Nice informative post for the forum, Rex
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post #3 of 42 (permalink) Old 01-16-2013, 04:17 AM
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Great thread
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post #4 of 42 (permalink) Old 01-16-2013, 06:05 AM
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Thank you - Very clear write-up/pics on this critical maintenance procedure.
It would be nice to expand on this if your cam sprockets don't line up spot on and how the offset woodruff keys are inserted and what offset you choose to buy by how you determine how much the marks are off. Pics of this process would really cap of the end of this DIY thread.
Great thread


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post #5 of 42 (permalink) Old 01-16-2013, 06:30 AM
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Great post and info. Let's make this a sticky.

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post #6 of 42 (permalink) Old 01-16-2013, 06:37 AM
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Great post and info. Let's make this a sticky.
This. Very helpful. Will be following this when I do mine.
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post #7 of 42 (permalink) Old 01-16-2013, 07:34 AM
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Refreshing

Refreshing to see a posting that REX will not get banned for as soon as it is posted.

Thanks for for really good information.

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post #8 of 42 (permalink) Old 01-16-2013, 01:48 PM
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terrrific write-up! Thanks for all the hard work on this. I am preparing to do this job for the first time, and this will definitely be my primary resource.

many thanks!

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post #9 of 42 (permalink) Old 01-16-2013, 02:06 PM
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Great thread. I do have one question- why did you choose the left bank to load the chain?
Most threads I've read used the right one.

I have my 420 to do. It will be much easier now that I have the right tools and know the pitfalls.
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post #10 of 42 (permalink) Old 01-16-2013, 02:24 PM Thread Starter
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Quote:
Originally Posted by KRH View Post
It would be nice to expand on this if your cam sprockets don't line up spot on and how the offset woodruff keys are inserted and what offset you choose to buy by how you determine how much the marks are off.
Any errors will result in time being wasted, how much time depends on what goes wrong. To start speculating all the possible errors one could make would just confuse and scare everyone, but I might add that once you start feeding the new chain there is no turning back. Regardless how bad you mess up the bottom line is you must obtain TDC and maintain it after several revolutions of the engine (by hand) before you even think about putting things back together. There are lots of little pitfalls along the way in any job, and to be "fair" this job is more or less an "advanced" DIY job. This job should not be tackled by persons not comfortable or familiar with internal combustion engines. Everything looks easy in the photos, but trust me these cars kick your ass.

Offset woodruff keys are usually only needed when something is worn, be it the sprockets (cam or crank), lower guide rails, chain stretch, ect.
Advancing or retarding a camshaft (aka "what offset") is dictated by the variables that are unique to every job, and as such I am unable to answer that question.



Quote:
Originally Posted by KRH View Post
Pics of this process would really cap of the end of this DIY thread.
Great thread
Well I am in the process of overhauling a 420 engine due to chain guide failure. It may be possible for me to cover other "more in-depth" issues while the timing cover is off. Remember, upper guides only buys you time... You still have more guides in the lower part of the timing cover. I will be addressing this most unfortunate fact in that write up.

Anyone thinking they should hold off on their guides need only look at this,



This photo above is the result of the left driver side inboard upper guide cracking and falling into the contact path of the chain and mid-sprocket (intended to drive a SLS pump, and idler on cars without).

At this point you need not worry about the lowers, as you might as well pull the cover at this point. One word... EXPENSIVE.

For people not aware of the lower guides,



While these guides have been relatively problem free, they still require replacement after time. I have heard reports of them letting go, but usually it's the uppers that buy the farm. Often times when the lowers let go they fall in the pan, but it's still a risk and the slapping/grinding of the chain would be heard.

There is also a guide on the oil pump chain tensioner, which I have also seen wear dangerously thin.

Sucks don't it?

Last edited by 126; 01-16-2013 at 02:55 PM.
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