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  #1  
Old 11-12-2002, 05:52 PM
96C220's Avatar
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Join Date: May 2001
Location: Hamilton, NJ
Posts: 367
How involved is replacing the timing chain guides on an 89 420 SEL

I have been reading more and more about the rails breaking and in turn ruining the head.
Honestly I'm starting to get scared. My car has 244k on the clock, and has been meticulously maintained by the previous owner (It was a one owner car of a family friend). I got it at 242k mi.

Scouring through the 3 ring binder of service records, I cant seem to find anything relating to timing chain, or guides & rails.

The mechanic who inspected it, and has serviced the car for years, assured me that it needed nothing mechanically, and that all is well. I specifically asked him to check chain stretch and guides, which he did...

But I cant help starting to feel like im driving on borrowed time.

I would at least like to replace the rails just for peace of mind if nothing else.

I have never worked on an MB engine beyond oil changes, plugs etc... Mostly maintenance stuff. I have changed the head gasket in my younger days, but that was on my old POS Olds Quad 4 that got me through college.

I do have the w126 service cd's and I will survey the procedure, but can just the guide rails be replaced relatively easily / quickly? From what I gather from reading here, this can be done via removing the valve covers.

Can the chain be untouched... i.e. left on while the guide rails are replaced?

Are there any caveats? How difficult a job would you consider this if you were to take your time and work methodically and slowly.

Are there any special tools needed? Also how much more difficult is rolling the new chain once you are in there?

How easy is it to mess this up?

Will a new set of guide rails prevent catastropic failure for a signifcant amount of time?

Sorry for all the questions - Im just rather worried about the whole sitation. - Do I trust the mechanic? Do I do it anyway? Honestly I look at this as a learning opportunity to get more experience with the car.

This car was purchased with the idea that most things would be done DIY, but im apprehensive to jump right in to something like this.

Best wishes and take care,
George
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George Androulakis

Former Mb's:

1990 500sl R129 - 76k Original Miles - New project - Follow the saga http://90r129.blogspot.com/
1990 190E 2.6 148k mi (sold)
1989 420 SEL 246k mi (sold)
1995 C220 175k mi (sold)
1992 190e 2.6 74k original miles (sold)
2000 c230 Kompressor 122k miles (RIP)
1996 C220 149k mi (sold)
2000 C230 Kompressor Sport 127k (sold)

Current Cars:

2009 Mercedes c300 4matic
2006 Mercedes s430
2005 Jaguar XJR
2003 Cadillac Escalade
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  #2  
Old 11-12-2002, 08:34 PM
MikeTangas's Avatar
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Join Date: Apr 2000
Location: So. Cal
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Actually replacing the guides on the V-8's is fairly easy, once you have all the accessories and their brackets removed. The chain stays in the block, you only have to mark the chain and sprocket on the driver's side, then remove the sprocket from the cam. Removing the sprocket allows access to the lower guide. Guides are held in by pins, removing the pin requires a special tool, or a proper sized bolt, a stack of washers and a socket (or similar sized nut).

Personally I would remove one valve cover and look at the guide to see what color it is. The guides are white when new and change color as they age. Yellow to light amber is probably still OK but getting close, beer bottle brown need to be changed ASAP.

The full procedure has been covered several time, some with pictures.



Showing the difference between old and new.
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Mike Tangas
'73 280SEL 4.5 (9/72)- RIP
Only 8,173 units built from 5/71 thru 11/72

'02 CLK320 Cabriolet - wifey's mid-life crisis

2012 VW Jetta Sportwagon TDI...at least its a diesel

Non illegitemae carborundum.
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  #3  
Old 11-12-2002, 10:24 PM
ILUVMILS's Avatar
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Join Date: Sep 2002
Location: New Jersey, U.S.A.
Posts: 2,461
Hi George Rolling a new chain in is easier than replacing the rails! As far as special tools, you'll need the right puller to remove the rail pins, as well as a valve spring compressor to remove the rocker arms. Don't be afraid to replace the tensioning rail while you're at it. The pin that it pivots on slides out easily if you can get a grip on it. I won't go into detail, but the job is quite straightforward, although it can be a bit intimidating for a first-timer. Let me know if you decide to go for it (at 244K I think you should ) and I'll try to help you out. Keep us posted
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  #4  
Old 11-13-2002, 12:23 AM
96C220's Avatar
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I took a look at the procedure on the CD

And now I have a lot more questions....

Taking the valve covers off seems pretty straightforward.

As does removing the alternator and power steering pump on their brackets.

Now... marking the chain and sprockets seems simple enough.

Here is where the questions come in.

Does the sprocket simply remove by removing the bolt that appears to hold it on?

Also is there enough slack in the chain to reattach the sprocket?

I noticed the caution about reinstalling it with the "collar" facing the wrong way.

Now I assume the washer / bolt trick to get the bearing pins out is simply a matter of threading the bolt onto the inside of the pin, and using washers between the pin and the head, to apply force to pull the pin out?

Next, How do you get the pins back in once you have swapped out the guides?? I couldn't seem to find any mention of that in the service manual... Are they just a friction fit?

Also there are three 131mm guides in the heads. Two on the drivers (left) side head, and one in the passengers (right) side head. Are those the ones that are succeptible to deterioration and failure?

There also appear to be two plastic slide rails in the lower part of the engine, near the crankshaft sprocket, specifially #87 or #79 on 340/3 from the 116 engine manual on the cd. - Should these also be replaced or do these not pose a problem?

It seems as though it would be a lot easier if the timing chain cover didnt have to come off....

The more I look at this, I get somewhat more confident, yet somewhat more intimidated at the same time.

Also does anyone have a parts list for this? I would like to order the stuff from fastlane - I will take a look and see what I can amass.

So far I'm thinking -

3 new 131mm guides
Timing Chain
Possibly a chain tensioner - If i can somehow get to that lower pin
Valve Cover gaskets

Did I miss anything obvious?

Thanks again,

George
__________________
George Androulakis

Former Mb's:

1990 500sl R129 - 76k Original Miles - New project - Follow the saga http://90r129.blogspot.com/
1990 190E 2.6 148k mi (sold)
1989 420 SEL 246k mi (sold)
1995 C220 175k mi (sold)
1992 190e 2.6 74k original miles (sold)
2000 c230 Kompressor 122k miles (RIP)
1996 C220 149k mi (sold)
2000 C230 Kompressor Sport 127k (sold)

Current Cars:

2009 Mercedes c300 4matic
2006 Mercedes s430
2005 Jaguar XJR
2003 Cadillac Escalade
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  #5  
Old 11-13-2002, 12:34 AM
MikeTangas's Avatar
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The three guides in the heads consist of 2 long and 1 short - don't remember the length. Yes, there is slack enough to remove the cam sprocket, all you need to do is loosen the tensioner and the sprocket is held on by that one bolt, but does have a keyway. If rolling in a new chain, by all means do the tensioner too. The tensioner is held to the block by 2 14mm bolts, that's it no pins at the tensioner. Also, if you decide to roll in a chain, change out the upper guides first as the old chain will afford a bit more slack.

To reinstall the pins, I used one of the fan bolts (6x50), threaded it in till bottomed, then tapped on the bolt head until pin was seated.

Not sure at what point the lower guides need replacing, but yes they require removal of the timing cover.
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Mike Tangas
'73 280SEL 4.5 (9/72)- RIP
Only 8,173 units built from 5/71 thru 11/72

'02 CLK320 Cabriolet - wifey's mid-life crisis

2012 VW Jetta Sportwagon TDI...at least its a diesel

Non illegitemae carborundum.
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  #6  
Old 11-13-2002, 12:56 AM
96C220's Avatar
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Join Date: May 2001
Location: Hamilton, NJ
Posts: 367
Ok that cleared the replacement of the pin issue up... More Questions

Now you mention the keyway on the cam sprocket. Can you elaborate on what that is? I'm not familliar with that terminology.

I'm assuming keeping correct time is a matter of marking chain and sprockets. Once the guides are replaced, and the sprockets put back on, set the chain over the sprockets so the dots line up again? Is that correct?

Also this may be a stupid question, but I'm assuming at some point that when you replace the sprocket, you would allign it so that when you tighten down the bolt, the mark lines up with the chain. - basically my question is there enough space between the teeth on the sprocket that a missalignment of the chain and the sprocket once replaced would be obvious?

Additionally what I'm trying to determine is if the lower guides (ones by the crankshaft sprocket) are also as vulnerable in causing a catastrophic failure, as the upper guides in the heads that are notorious for breaking off....

Finally, will the pins come loose at some point? Or will they have to be yanked out the entire way?


The determination of rolling a new chain in or not will I guess be made while I am in there.... If the chain is fairly streched I suppose it would be best to replace it.

If it seems intact, I would want to replace the guides, as that is what has me holding my breath every time I start the car (since most of the failures have been at idle upon startup).

Sorry for all the amateuristic questions, but I just want to make sure I clear any doubts I have in my head before I actually go tearing into the car.

Thanks again for all the help.

George
__________________
George Androulakis

Former Mb's:

1990 500sl R129 - 76k Original Miles - New project - Follow the saga http://90r129.blogspot.com/
1990 190E 2.6 148k mi (sold)
1989 420 SEL 246k mi (sold)
1995 C220 175k mi (sold)
1992 190e 2.6 74k original miles (sold)
2000 c230 Kompressor 122k miles (RIP)
1996 C220 149k mi (sold)
2000 C230 Kompressor Sport 127k (sold)

Current Cars:

2009 Mercedes c300 4matic
2006 Mercedes s430
2005 Jaguar XJR
2003 Cadillac Escalade
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  #7  
Old 11-13-2002, 02:13 AM
MikeTangas's Avatar
Senior Member
 
Join Date: Apr 2000
Location: So. Cal
Posts: 4,430
The keyway is just a slot cut in the sprocket end of the cam shaft, with a matching slot cut in the bore of the cam sprocket, a small square key fits in the slot and retain sprocket to cam alignment (might be a woodruf key - one side is semi-circular). Because of the keyway, the sprocket only goes on one way.

Mark the chain and sprocket with paint. When you remove the sprocket and chain, from the driver's side head only, you can then lay the sprocket aside, separate from the chain. Upon assembly, make sure the paint marks line up and the key will ensure everything is still timed.

Here is what it should look like:



Once the pins are about halfway out, then come out pretty easy.

Search for a post by me, titled "560SEL accomplisments". About halfway through this long thread is some timing chain info.
__________________
Mike Tangas
'73 280SEL 4.5 (9/72)- RIP
Only 8,173 units built from 5/71 thru 11/72

'02 CLK320 Cabriolet - wifey's mid-life crisis

2012 VW Jetta Sportwagon TDI...at least its a diesel

Non illegitemae carborundum.
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