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1974 450SL (US), 2005 SLK200 (UK)
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Discussion Starter #1
I am now ready to start this - the tear down of the front of the engine is complete. I have watched PanzerPuff's video and done a bit of research and come up with a list of steps. Have I got anything out of order or missed anything off? I am a bit unsure as to exactly when the chain needs full tension, partial tension and OK with no tension.
  1. Rotate engine to find old master link (nowhere near TDC), positioned on right sprocket ready for chain replacement later
  2. Put witness marks on both sprockets and chain
  3. Remove old tensioner
  4. Cable tie chain to old right sprocket?
  5. Remove old right sprocket
  6. Tie chain to hood with bungee cords
  7. Remove old right-hand guides
  8. Install new right-hand guides
  9. Transfer mark from old sprocket to new
  10. Install new right sprocket
  11. Cable tie chain to old left sprocket?
  12. Remove old left sprocket
  13. Tie chain to hood with bungee cords
  14. Remove old left-hand guides
  15. Install new left-hand guides
  16. Transfer mark from old sprocket to new
  17. Install new left sprocket
  18. Install new tensioner but don’t fully install – spacer needed?
  19. Cable tie chain to right sprocket
  20. Install new chain
  21. Fully install new tensioner
  22. Install new oiler tubes
  23. Rotate engine several times to check
Thanks, Andy

2616884
 

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1988 560SL
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61 Posts
One additional step I did before closing everything back up was to disable the ignition and crank the engine (with valve covers still off) for a few seconds to confirm that the oiler tubes were getting a good stream of oil on all the cam lobes. You'll want to put rags all around each side to catch any oil overflow, and there will be some oil splatter from the rotating cams, but I felt this step was worth it for peace of mind that the oiler tubes were back on correctly and putting oil where they should.
 

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'79 450SL, '04 CLK200 convertible; former A124, W210, A209.
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1,252 Posts
One of the most critical steps is to cover all openings around chain and distributor holes - there are some horror stories about bits & pieces going missing down those openings, and that's a big NO-NO!

Have a look at this thread, heavily inspired by PanzerPuff's video you linked, and some looksee pics are here 1979 Mercedes 450SL Restoration
 

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1987 560SL (L.Tonk) [92,700 miles]
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262 Posts
One of the most critical steps is to cover all openings around chain and distributor holes - there are some horror stories about bits & pieces going missing down those openings, and that's a big NO-NO!
This cannot be stressed enough. I had a washer bounce three times around the engine and somehow get under the plastic I had draped over "the abyss". It was just balanced on the edge, and I was able to retrieve it with a magnet. Lucky I was wearing brown pants.
 

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'79 450SL, '04 CLK200 convertible; former A124, W210, A209.
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1,252 Posts
@andya This is the thread I meant to link in my earlier post

 

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1974 450SL (US), 2005 SLK200 (UK)
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230 Posts
Discussion Starter #6
@andya This is the thread I meant to link in my earlier post

Many thanks - OK, so you replaced the chain with tensioner out.

Andy
 

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1984 380SL
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63 Posts
Andy,
If the chain has not been replaced before, there will be no master link. When I changed mine, I set the engine at TCD, verified the cam sprockets were lined up and then cut the chain (dremel'd the links out) and used the new master link to attach the new chain to the old and then rotated it on.
 

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1974 450SL (US), 2005 SLK200 (UK)
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Discussion Starter #8
Andy,
If the chain has not been replaced before, there will be no master link. When I changed mine, I set the engine at TCD, verified the cam sprockets were lined up and then cut the chain (dremel'd the links out) and used the new master link to attach the new chain to the old and then rotated it on.
Yes. I was quite surprised when I saw a master link. Saves me from cutting the chain. Car has 168k miles and chain has 12 deg of stretch. Guides are coffee colored. So it must have been done a long time ago.

Andy
 

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1988 560SL
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61 Posts
12 deg of stretch? My car has similar overall mileage (160k) and prior owner record showed chain/guides/tensioner had been replaced at 90k (but over 20 years ago). When I lined up my timing marks on the cams I was only a couple of degrees off TDC on the crank, so I decided to not replace the chain and only do the guides, tensioner and oilers. The guides were all coffee and brittle. The inboard one on the drivers side was actually broken, but luckily I was able to get all but a small 1/4in size piece out. I'm guessing that piece is down at the bottom of the pan and not causing any problem. I'll keep an eye out for it when I change my oil, and if not try to put a borescope up the drain plug to see if I can see it to fish out.

What causes a timing chain to stretch at different rates anyway?
 

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'80 450SLC Afro RHD Ikonengold
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2,855 Posts
What causes a timing chain to stretch at different rates anyway?

When rotating the engine whilst replacing the chain, you will notice that the chain comes out dry. It seems it is lubricated by means of splashes which in turn means frequent long no-run periods will allow drain of oil from links to bare minimum.
If there are 200 rollers in the chain, 0.05mm wear per link will translate to 10mm elongation or approx 1 tooth at the cam.
 

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1988 560SL
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61 Posts
That's interesting that the chain can also suffer from long no-run periods. I know when I was in the market to purchase my car, I was looking at one with lower mileage (at a higher price) and after getting a copy of the service records for that car went to talk to the indy mechanic who had done most of the service for the car over its entire life. He advised me away from that car because it had been in storage for 10 years (even though he did confirm from personal experience it was stored in a climate controlled garage in colorado). Said these cars don't "sit well" and as I was looking for a car that I wanted to drive regularly (i.e. daily drive for most part), advised me to not be afraid of higher mileage if car had good service records and had been driven regularly. The one I bought (with about 155k miles) had been driven regularly about 3k per year since prior timing chain replacement 20 years ago, and as my inspection showed, only stretched 2 deg over that 60k miles. I was pleasantly surprised that I all of the cam lobes were also mirror polish finish (with hardly a scratch) after 160k miles.
 

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1987 560SL
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2,329 Posts
Andya, your checklist looks good. I assume you are using two cable ties on each sprocket in leapfrog fashion. This job needs removable cable ties, lots of picks on amazon or ebay
Your question about chain tension is really not an issue. Just don't allow the chain to jump the sprockets, and the cable ties take care of that. The chain tensioner does not get bolted down until the end, and then it is just the mechanical spring that pushes against the new chain. The real force behind the chain tensioner is oil pressure, that occurs on startup and while the engine is running. Best of luck to you on this job.
 

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1974 450SL (US), 2005 SLK200 (UK)
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Discussion Starter #13
Andya, your checklist looks good. I assume you are using two cable ties on each sprocket in leapfrog fashion. This job needs removable cable ties, lots of picks on amazon or ebay
Your question about chain tension is really not an issue. Just don't allow the chain to jump the sprockets, and the cable ties take care of that. The chain tensioner does not get bolted down until the end, and then it is just the mechanical spring that pushes against the new chain. The real force behind the chain tensioner is oil pressure, that occurs on startup and while the engine is running. Best of luck to you on this job.
Many thanks for the confirmation. I don't think I would even consider tackling this job if you had not made your video. Andy
 

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1986 560SL with M120 V12 Engine, 1988 560SL Stock
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9,834 Posts
Did not see anything about replacing the chain tensioner rail. This will require removal of the alternator. It is more important to replace this rail than the other three as it is the rail that actually wears and allows the chain to slap the head. The tension rail never breaks but looseness of the chain will cause the other 3 to break.
 

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1974 450SL (US), 2005 SLK200 (UK)
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Discussion Starter #15
Did not see anything about replacing the chain tensioner rail. This will require removal of the alternator. It is more important to replace this rail than the other three as it is the rail that actually wears and allows the chain to slap the head. The tension rail never breaks but looseness of the chain will cause the other 3 to break.
Ah, I just regarded it as another form of a guide. Alternator is removed. Incidentally PanzerPuff showed in his video that he purchased an entire new rail. I've only purchased a new plastic surface/lining. I didn't understand the benefit of replacing the metal part.

Andy
 

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1974 450SL (US), 2005 SLK200 (UK)
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Discussion Starter #16
When removing the sprockets from the camshafts it's my understanding that the camshafts might move slightly. Is it best to do this with the engine at TDC or does the engine position not matter?

Thanks, Andy
 

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1988 560SL
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If I remember correctly it's the driver side one that will clock just a bit due to a little torque on the shaft from the valve springs. You want to remove the sprockets when the woodruff key on the shaft is on the top side (which I also believe corresponds to TDC). There are other posts about the woodruff key flying out (or worse falling down into the engine), so I was very nervous and put a telescoping magnet pointer on the woodruff key as I pulled the sprocket off so the magnet would catch the key if it came out. I don't recall mine coming out though, and put some tape around it after sprocket was off to keep it in place.
 

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1986 560SL with M120 V12 Engine, 1988 560SL Stock
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9,834 Posts
Ah, I just regarded it as another form of a guide. Alternator is removed. Incidentally PanzerPuff showed in his video that he purchased an entire new rail. I've only purchased a new plastic surface/lining. I didn't understand the benefit of replacing the metal part.

Andy
Sometimes you have to replace the whole thing if it gets completely worn to the metal. Also you have an early model 117 engine which should have came from the factory with metal upper guides. If those are still there, I wouldn't replace them unless they are very worn.
 

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1986 560SL with M120 V12 Engine, 1988 560SL Stock
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9,834 Posts
When removing the sprockets from the camshafts it's my understanding that the camshafts might move slightly. Is it best to do this with the engine at TDC or does the engine position not matter?

Thanks, Andy
Yes the cams will want to rotate. It might be advantageous to take the rockers out first to make things easier to work with.
 

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1974 450SL (US), 2005 SLK200 (UK)
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Discussion Starter #20
If I remember correctly it's the driver side one that will clock just a bit due to a little torque on the shaft from the valve springs. You want to remove the sprockets when the woodruff key on the shaft is on the top side (which I also believe corresponds to TDC). There are other posts about the woodruff key flying out (or worse falling down into the engine), so I was very nervous and put a telescoping magnet pointer on the woodruff key as I pulled the sprocket off so the magnet would catch the key if it came out. I don't recall mine coming out though, and put some tape around it after sprocket was off to keep it in place.
That is a really good point - thanks! Because the old master link is nowhere near TDC I was focused more on getting that correctly positioned. What I will do instead is break this up into two separate stages - TDC and replace sprockets, guides and tensioner, then rotate to find the old master link and replace chain.

Andy
 
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