W108 4.5L Timing Chain Questions - Mercedes-Benz Forum

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post #1 of 17 (permalink) Old 08-06-2016, 11:15 PM Thread Starter
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Question W108 4.5L Timing Chain Questions

Hello Everyone,

I have a 72 280SEL 4.5L with (presumably) 137k miles. I am the second owner, i have had it for 2 years. I bought all of the parts to replace the timing chain and guide rails as preventative maintenance. Upon pulling the injectors (replacing), opening up the valve covers and rotating the crank a few times, I noticed a master link....so this has been changed before. I looked at the guides, and they are NOT factory, though they appear to be in good shape.

I contacted the previous owner to see if he recalls when it was changed. He said that he followed the Mercedes recommended maintenance guide to the letter, so if it was in there, that's when he did it. I don't have the guide anymore, so I'm assuming it was changed at 100k miles. So far, no need to swap it out right now.

Timing guides (NON FACTORY) showing minimal wear, however they don't look anything like the factory plastic ones...http://i.imgur.com/7jEnrub.jpg
Master Link (can you tell the chain brand from this?): http://i.imgur.com/8t9TVxp.jpg

But there are a few things that bother me. I'm not totally convinced that they did the timing right when they replaced the chain. The master link is nowhere near TDC, which isn't necessarily bad by itself, but in the images below you'll notice that the 0 mark on the crank doesn't seem to match the TDC mark on the distributor, which doesn't seem to quite match the marks on the cams.

Crank Timing Mark: http://i.imgur.com/qsP4Vn2.jpg

Passenger Cam Timing Mark: http://i.imgur.com/J0f57F0.jpg

Driver Cam Timing Mark (slightly off the point): http://i.imgur.com/utu43PD.jpg

Distributor Timing Mark (off the point): http://i.imgur.com/1ovHdQD.jpg

SO, my questions are:

1) Is my timing jacked up between the cams, distributor, and crank?
2) If so, how do I correct this?
3) Why don't I have a clearly labeled "0" mark for TDC?
3) Where did these super thick non-factory guides come from? Is it just a different brand?


I don't want to change the timing chain and guides just to do it. These parts are expensive and I'd rather save them for when they're actually needed than prematurely replace the existing chain.

HOWEVER, I am concerned about those guides, and my timing. Should I pull the driver side gear off and adjust the chain seating by one link? Is the distributor way off? The crank isn't exactly at 0 when the cam marks are at 0, so is the crank timing off?

If you have any input here, I'd appreciate it!
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post #2 of 17 (permalink) Old 08-07-2016, 07:08 AM
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On the early v8 cars, the timing chain guides are/were metal with a black lining. These don't break like the cheaper later guides. If not totally worn out, I suggest keeping the metal-backed guides.

I would expect the passenger (in a LHD car) cam to be the one that is off because there is much more chain between it and the crank. Seeing that the driver (presumably the left side on a LHD car) is far off, I MIGHT consider spending some more time investigating that issue.

The distributor can simply be twisted or re-inserted so it hits TDC. So that does t concern me. But before you pull the distributor out, take a photo of where the rotor points. Don't assume the crank TDC is the TDC for the distributor and cams, as the crank has two TDC per one TDC for the distributor.

Here's what I would do:

Tighten the tensioner if you have loosened it from the engine.

Crank the motor by hand with your 27mm socket and breaker bar making an attempt to stop on the markers for each camshaft. Get the reading on the harmonic balancer for how far off you "measure" the "chain stretch" is when measuring from each cam. It's not really "chain stretch", but that's how people usually measure it.

You can get offset woodruff keys for the camshaft sprockets if you determine the timing is far enough off. But before you order, you should make sure your car is not already using offset woodruff keys.

Since the car shows signs of the chain slapping the heads, you should not rule out the possibility of the chain having jumped a tooth. That could be a reason for mixed up timing. Take your time to analyzed what's happened.

Take a good look at your camshaft sprockets looking for wear which will add to the "chain stretch" because worn sprockets equate to a shorter path for the chain to follow and most chain slack. Camshaft sprockets are easy to replace. The chain is easy to replace too.

Check the tensioner. From what I've read, the cheap febi tensioner for this model engine isn't the bad one to avoid like it is on the later v8 engines. So you might decide to slap in a new tensioner, but you should probably at least pull the old tensioner or at the very least see how hard it is to press the tensioner rail. If the spring is soft, or if the tensioner rail doesn't push right back into place with strong force, that could be the cause of the marks in the head. Lack of oil pressure on startup means the spring has to do all the work, and the springs wear out. If the oil passages are clogged, then that's really bad. How did the oil look when you bought this car? Shavings from the head could also contribute to a clogged tensioner.


Since you've got it open and got all/most of the parts for the job, you might want to proceed and have a determine date/mileage at which you know the service was done. It's been a lot of time probably. Right? There's piece of mind.

But those metal guides, you'll want to keep them.

.

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post #3 of 17 (permalink) Old 08-07-2016, 07:21 AM
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The crank mark is the line with the "0" just touching it. in your picture you are on the 10.

Based on that your chain has stretched to the point in needs replacing.

the left and right cams are often off by a few degrees. there are offset woodruff keys to compensate for that once you have a new chain in.


The disti doesnt care what angle it is installed as long as the timing is correct. I dont recall if the disti gear has multi teeth, if so if could be off by one.

The guides look good.
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post #4 of 17 (permalink) Old 08-07-2016, 08:03 AM
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Originally Posted by envoy_to_the_Stars View Post

If you have any input here, I'd appreciate it!
Fonzi has covered most of your concerns.

- Guide in your picture looks original and same as my original guide as can be seen in picture below. (Originals were NOT plastic, but that is what you get if you order new ones now) Chain wear marks on my car too and probably on most cars of this age and part of reason chain would have been changed. Tensioner should have (and may have) been changed at same time.



- As Fonzi said, distributor marks are not an issue. The mark is used when initially inserting the distributor, but after that ignition timing is adjusted by rotating the distributor. It won't end up on the mark. Not sure why you have two marks, except someone might have used one as the starting point when inserting distributor because it rotates on gear as it goes down into place.

What you could do first:

- Using crank or PS pulley, rotate engine in direction of rotation only, clockwise facing engine) so that passenger side (RH side facing forward) cam marks line up. Then note where crank pointer is relative to balancer markings and same time, note where driver side cam marks are.

If tensioner has not been in service for a while, it will probably have leaked down, so when checking, hold the passenger side cam on it's mark with a second wrench while tensioning the chain at the crank. In other words, make sure the chain is fully tensioned between the passenger cam and the crank.

This would give you (and us) readings that are accurate. Then next step would be to decide what you need to do, if anything.

The balancer pointer should be close to the 0 (TDC) mark where your pic has a white dot (mid way between the 5s - the stampings are a bit confusing)

The master link could be anywhere really.

You might check for sprocket wear. Can't see too much of your sprockets in pics, but they don't "look" bad. This link has some good info on checking for wear and what affect it could have on what appears as "stretch" http://www.benzworld.org/forums/r-c1...placement.html. It's on my to-do list!

1972 350SL 4.5L - MBGraham, near Kingston, Ontario

Last edited by MBGraham; 08-07-2016 at 10:00 AM.
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post #5 of 17 (permalink) Old 08-07-2016, 10:50 AM Thread Starter
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Thanks to everyone for taking the time to give me such fantastic feedback so far! Based on everyone's input, here is my plan of attack:

1) Replace the chain, leave the guides. If I'm 10 degrees off of TDC when the cam marks are on (or close to on) point, replacing the chain would be the quickest way to get everything back in order.
2) Replace the Tensioner. I already have one, and the one in the car looks original - so why not replace it.
3) re-spin the engine from the crank pulley and check the position of the cam/balancer marks.

I'll keep everyone updated!
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post #6 of 17 (permalink) Old 08-07-2016, 10:55 AM
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Sprockets are cheap, and they could be the thing that needs replacement instead of, or in addition to, you chain. Chain is about $100. Cam Sprockets are about $25 each.

If you don't know how to check the cam sprockets for wear, replace them.

.

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post #7 of 17 (permalink) Old 08-07-2016, 05:51 PM
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I would at least inspect the guides....even if they are the metal ones. Why? Because my 280SEL 4.5 had a broken metal guide in it when I did the chain. (also had a broken plastic one) I now have the cheap plastic withthe knowlege that I have to change them every 100k at least. Good news is they are really pretty easy to do. On the other hand, mine had 400K+ on the clock whenI did it.

The cam sprockets are 36 tooth which is ironically 10 degrees per tooth. It could be you have jumped a tooth (but that would mean BOTH cams jumped one tooth and one tooth only) or the PO could have used a moderately incompetant shop, or you have a bunch of stretch in your chain and/or a bad tensioner.

Whatever the case, repair/replace prior to doing anything.
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post #8 of 17 (permalink) Old 08-07-2016, 07:26 PM Thread Starter
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Well, I have a bit of an unfortunate update.

I used "heavy duty" zip ties to hold the chain to the sprocket when removing the old master link. But Unfortunately, one of the ties snapped when I pulled the link out, letting the length of chain go limp and fall down.

I removed the guide and was able to recover the chain end, but I'm obviously not strong enough to recreate the tension that was on it originally. Therefore, I have a 2 link gap.

See: http://i.imgur.com/0ihPaTK.jpg

And: http://i.imgur.com/uJoc2zrr.jpg

Nothing else has been moved. I haven't taken out the tensioner, because I'm too concerned about creating more slack in the chain. I looked down into the engine, and the top idler pulley is still moving freely, and i haven't skipped any links there...I just cannot physically pull the chain hard enough to get it back to its original spot.

I'm not exactly sure how to proceed given the gap. HELP!
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post #9 of 17 (permalink) Old 08-08-2016, 07:23 AM
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I would take out the tensioner. it removes slack on the backside of the chain. the other side is the one that has to line up the crank and cams. Remember you were already 10 degrees which is one cam tooth off when you started.

This may be helpful also
PeachPartsWiki: M116/117 Timing Chain Replacement
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post #10 of 17 (permalink) Old 08-08-2016, 07:48 AM
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Which side are you working on first? I had a similar thing happen. I also dropped one end (on the Left hand side) and when I recovered it, it had a kink in it where two links had folded back on themselves. I had to drop it back down and coax the links to straighten out by pulling some slack back to the right hand bank, then pulling it back to the left hand bank with tension on it. Just remember, the engine isn't running and as long as you are not beating on things, you wont hurt it. Just make sure everything is at TDC and on the marks when you finish.
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