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  #1  
Old 12-03-2007, 12:40 AM
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Timing Chain Oops / Fixing jumped chain links

I am a newbie and may have taken on a task slightly above my level of expertise when I decide to change the timing chain on my '84 380 SL today. The set up went smoothly. However, there was a miscommunication with my 'assistant', and the new chain wasn't held flush to the passenger side sprocket as the engine was rotated. This happend twice within the first 14 links, at which point, we stopped.

I know...this seems ridiculous. However, given my current situation, i am in need of some sound advice to remedy the problem so I can finish the timing chain replacement.

Once the chain jumped the sprocket, I pulled the chain back into place. The second time i had to pull harder to get the chain to seat in the sprocket. It appeared that I had taken out the slack, and the chain was correctly situated. However, as I tried to turn the engine, after a couple degrees of rotation, I encountered resistance, and can no longer turn the engine.

The chain on the passenger side is pulled taught...to me it seems unnaturally taught.

My friend and I debated 2 possibilities of why the egine is bound.

1) When the chain jumped the sprocket, the engine turned, but the passenger sprocket did not, resulting in it being possibly a tooth or more behind the engine.

2) When I pulled the slack chain back and pressed it back on to the sprocket, it forced the passenger sprocket to rotate ahead 1/2 tooth or so.

I am assuming whether the passenger sprocket is ahead 1/2 tooth or behind 2 or 3, the result is the same, that the pistons and valves are out of sync resulting in interference, and preventing further rotation.

Since I have only turned the engine ~180 deg past TDC, my thought was to try to measure the angle rotated on both the right and left sprockets to determine if it the passenger sprocket is ahead or behind. I was attempting to do this with a piece of thread from the notch and mark indicating top dead center on each cam tower, but it became to dark to work.

If anyone can suggest a way to get the sprocket back in sync, that doesn't involve a dealership, I would be extremely grateful.

Thanks,
Justin
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  #2  
Old 12-03-2007, 06:59 PM
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you can do it,

before you attempt anything ,use the search button at the top of this page ,type in '' 380 timing chain replacement '', you will find much valuable information ,
good luck
Brian

Last edited by Benz Mercedes; 12-03-2007 at 07:14 PM.
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  #3  
Old 12-03-2007, 11:24 PM
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What method did you use to do this? The shop manual? A website?

A. Did you remove the spark plugs?
B. Did you remove the RH (passenger in US) cam followers (rocker arms)?
C. Did you remove the tensioner (hopefully, to replace it?)

The reason I ask about "B" is that some instructions don't suggest that this is required but the MB shop manual does. This scenario is the reason why.

You DID remove _one entire link_ from the old chain before attaching to the new one, right?
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Last edited by Strife; 12-03-2007 at 11:30 PM.
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  #4  
Old 12-04-2007, 12:29 AM
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Brian,

Thanks for your suggestions. I have looked through many posts, but am struggling to find information about what must be done to correct a jumped cog.

Strife,

My references were a booklet on avoiding catastrophic engine failure from **************.com, as well as numerous posts on this forum, and the DIY guide to changing the timing chain also on this site.

1) The spark plugs are out.
2) The RH cam followers are not removed. There were mixed reviews about whether or not this was necessary, so i left them in to save time.
3) I was unsure about the tensioner. I left it in, with plans to change it at the end.

Yes, i filed off the rivets from one chain link and pushed the pins back to remove a link in the chain and then used the new connector chain link with the c-clamps to attach the new chain to the old.

To be clear, do you think the binding of the engine is due to me not removing the cam followers rather than my assumption of the chain being off on the passenger cam cog?

Thanks very much to you both,
Justin
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  #5  
Old 12-04-2007, 12:53 AM
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No, the RH rockers being in AND the engine being mechanically timed right could not cause this. If it was timed right the engine would turn OK with them in or out.

The good thing about having the RH rockers out is that this puts 50% of the valve springs out of the picture so that there is 50% less opportunity to jump while pulling the chain through. Also, with the rockers out there is no possiblity of hitting anything on that side even if things get out of whack during chain installation - it's possible to readjust the RH side before reconnecting the chain even if you miss a tooth or two by lining up the indicator on the cam bearing to the indicator on the gear.

I have some ideas on how I would proceed but I would like to defer to people with more experience. Don't "jump" to action on this.

The cams turn 1/2 of the crank. Each tooth represents a lot of degrees.
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  #6  
Old 12-04-2007, 01:03 AM
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Thanks again, Strife.

My plan is to give it a few days to research and attempt again on Saturday morning.

Take care,
Justin
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  #7  
Old 12-04-2007, 09:54 AM
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HI
you are doing the right thing replacing the chain I recently rebuilt a 350 that had jumped a link and damaged all of the exhaust valves on the drivers side. Here is a pic of the chain with the timing cover off (if you need a bigger pic email me ). if you are only 14 links in you have not even got to the first sprocket yet and something else is wrong.

Its a really simple job if you just take it slowly and do 2 or 3 links at a time. Ive done 5 or 6 of them now and you just have to take it slowly. Whatever you do if you get it wrong dont panic (like the hitch hikers guide). you can sort it out fairly easily. Dont try and take the timing cover off (Ive never done a 380 but assume its the same as the 350 and 450"s, just a single link chain) as you have to remove the sump to pull the oil pump cog and for that you have to remove the engine.

good luck
Barri
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61 Austin mini
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  #8  
Old 12-04-2007, 10:02 AM
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wierd my picture didn't post. have a look at this page on my website

http://britautorepair.com/interest.htm
__________________
61 Austin mini
67 Lotus 7
74 450sl
76 Cadillac 8.2l (501 ci)

some new cars

megasquirt conversion on:
djet 74 450sl http://www.mercdjetmegasquirt.britautorepair.com/
cis 76 450sl http://www.merccismegasquirt.britautorepair.com/

the best view is always from the point of no return
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  #9  
Old 12-04-2007, 01:05 PM
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Barri,

Fantastic pics. This really helps me to visualize what is going on. Still having trouble figuring out how to determine how to make sure the timing of the upper center and passenger side cam cogs are timed with the rest of the engine. I agree, i want to avoid taking the front of the engine off at all costs.

THANKS!
Justin
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  #10  
Old 12-04-2007, 03:42 PM
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HI Justin, its always nice to "see" what you are trying to do. Look at it this way the middle top cog and middle right cog are blind cogs, either to control the chain run or drive the distributor. So as long as you have an open chain end on the passenger side camshaft you really only need to keep the drivers side cam and crank in synch as the chain is broken on the passenger side cam so you can reset the cam to where it has to be and then put on the master link. Resetting the distributor is easy at that point as you can always run the chain master link to the drivers side cam, pop the link loosen the chain and reset the distributor drive (not easy but doable) and tension the chain back on the drivers side can and put the master link back on. Just remember the distributor drive is takes (my memory is going again) 7 full revolution to get back to TDC (I hope I got that right I know how to do it but have never counted as I know what I am looking at).
I would be more worried to find out what you are hitting that is stopping the engine turning. at 14 links in (so long as you kept tension on the old chain coming out) something in the engine has to be hitting. There simply are not enough links in there to be sticking on something. I would double check that your cam is not out of synch. did you set the engine at TDC to start and check that both cam marks were showing alignment?

Remember if you have skipped links, just reverse the process back to TDC and then start again.
cheers
Barri
__________________
61 Austin mini
67 Lotus 7
74 450sl
76 Cadillac 8.2l (501 ci)

some new cars

megasquirt conversion on:
djet 74 450sl http://www.mercdjetmegasquirt.britautorepair.com/
cis 76 450sl http://www.merccismegasquirt.britautorepair.com/

the best view is always from the point of no return
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  #11  
Old 12-04-2007, 04:54 PM
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Thanks again, Barri!

My friends and I were troubleshooting this over e-mail earlier.

What we know:
1) cams were at TDC to start; they were slightly off (didn't measure angle, but it was approx the width of the notch to line up TDC), assumed due to chain stretch.
2) Driver cam cog and Distributor cog are in sync
3) Currently both the passenger and driver side cam cogs are ~180deg from TDC. May not be in sync, but both were rotating
4) New chain on passenger cam cog jumped twice as we rotated crankshaft
5) Old chain was not held totally taut as engine was rotated, so there may have been enough slack on old chain to free it from crankshaft. However, I was in a position where i was kind of looking at the driver cam cog as i rotated the engine. I believe that it continued to rotate, which would indicate that the crankshaft did not rotate freely...however this is unconfirmed.

What we don't know:
6) There may be a 'wrinkle' or overlapping chain link between the upper middle cog and the passenger cam cog
7) The passenger cam cog may be out of sync with the system (was not rotated when chain jumped or over rotated when chain was re-meshed with cog)
8) The crankshaft might have rotated independent of rest of system. (i think this is improbable, but don't want to rule it out)


My first question: can i rotate the engine CCW? The directions say not to...but at this point, it seems like i ahve to undo what i've done.

Assuming that is acceptable:
Here is my instinct on how to proceed:
A) Allow slack in the chain on passenger cam cog, and using flat blade screwdriver or other, pull chain down and toward passenger cog to ensure it is meshed with upper cog.
B) Pull slack up around passenger can cog and lock in place w/ vice grips or zipties.
C) remove chain tensioner
D) Pull chain taut from crankshaft toward passenger cam cog.
***break***
At this point, I would assume that I have taken out any wrinkles in the chain. If the engine will still not rotate, it would be due to interference.

E) Measure the rotation from TDC of both cam cogs. ***Method to be determined. Open to suggestions.

F) If both cam cogs not in sync, test if passenger cam cog can rotate free of timing chain. If yes, rotate one tooth at a time, re-mesh chain and try engine rotation. Record cog movement at each step.

Is this a reasonable start? and how would you proceed if both cam cogs are synced, or if passenger cam cog won't rotate freely?

Thanks again,
Justin
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  #12  
Old 12-04-2007, 06:19 PM
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HI Justin
here is a good article by tomguy from this site

http://www.peachparts.com/Wikka/M117TimingChain

If you are sure you have only put 14 links into the engine by turning the crank clockwise just keeping everything else in position, then I would turn the passenger cam shaft counter clockwise and pull out the slack between it and the drivers side cam being sure to stop before the drivers side cam moves that way you have all of the slack out between the top of the drivers cam and the top of the passenger cam (the middle top wheel is a free wheel, it drives nothing so can turn anyhow)

then I would try to get any slack out of the system between the crank gear and the passenger side cam by pulling up on the old chain on the passenger side (I would while the chain is being pulled up and under tension turn the crank counter clockwise to get any slack out between the drivers cam gear back round to the passenger cam gear on the tensioner side) . this should put you at a point where everything is tight and the cogs are all out the equivalent of 14 links.

Keeping the tension on the chain coming up past the tensioner very slowly and carefully turn the engine back the 14 links you have fed in. reattach the old chain with the master link and check everything is still where it should be at TDC (where you should now be)

if all is correct start again and use the guide above from tomguy, its a one person job with very little chance of a mistake, just keep clamping and unclamping methodically. takes 1 person about 15 minutes to change the chain. check everything is OK at TDC and dont forget to check the distributor as well. then do yourself a favour and pull the alternator and the power steering pump and replace the 3 plastic top chain rail guides.

Dont ever turn the engine CCW unless you can guarantee that you have full tension on the chain and are pulling like mad! under normal conditions if you turn CCW on the engine crank bolt the tensioner will be pushed in by the pressure and you have a big chance of jumping teeth.

hope that helps
cheers
barri
__________________
61 Austin mini
67 Lotus 7
74 450sl
76 Cadillac 8.2l (501 ci)

some new cars

megasquirt conversion on:
djet 74 450sl http://www.mercdjetmegasquirt.britautorepair.com/
cis 76 450sl http://www.merccismegasquirt.britautorepair.com/

the best view is always from the point of no return
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  #13  
Old 12-04-2007, 07:53 PM
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The above is similar to what I was thinking - get ALL of the slack out between the crank and the LH side timing chain, if any, and very slowly go CCW from there, making certain that everone is pulling on the chains and keeping the passenger side chain _on the sprocket_. You will need at least one and maybe TWO _reliable_ helpers to do this. If it was not jammed up to the point where you are, it will not get jammed up going the other way, _if no further slippage takes or has taken place_. OF course, force NOTHING. _Expect_ the RH side to want to jump as springs get unsprung.

Once you get the crank back to 0, and, we hope, the LH side on the cam/cam tower marks lined up, you should be able to get the other side on the marks also. At that point, you can go again. It will be interesting to see how far you slipped.

BTW, it is good to get in the habit of calling the US driver side the LH side and the US passenger side the RH side, which is the same in all countries. If someone from England or Aus reads this for any advice, they are in BIG trouble, for obvious reasons.

I bought a chain cover ($50) for this job, which I've used twice. I looked at its purchase as divorce insurance. With this tool, it's impossible to have the RH side jump the chain even if you are working alone. But my "assistant" and I screwed up anyway, when a rag stuffed in the head's chain passage to keep chips out wound up between the chain and the cam sprocket.

Someone on this board's "assistant" dropped the chain in the engine during this job. It was recovered, and, AFAIK, they are still married.
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  #14  
Old 12-05-2007, 11:49 AM
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Barri and Strife,

Thanks for the suggestiosn. Sounds like a solid plan, and i appreciate the step by step process and pointers. We will give this a shot Saturday morning. I'll be sure to post what I find out, and also try to include some photos.

Thanks!
Justin
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  #15  
Old 12-10-2007, 01:59 PM
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Newbie Timing Chain and Chain Guides Debrief

Thanks to all that provided advice and suggestions. Moxie, my '84 380SL, is running better now than she has in well over a year. And now I can rest easy that I don't have bits of chain guide floating around the inside of my engine.

Here is a lengthy debrief of some lessons learned, mostly through mistakes made. This was the first time I really got under the hood of my Mercedes, so many of these mistakes wouldn't be made by someone with Mercedes or just general auto repair knowledge. I hope that these will help other users, especially newbies, avoid problems as they do these repairs.

1) Before you can work on the guides or the chains, you must remove the valve covers. Most instructions will tell you to unhook and plug fuel lines, as well as the break booster line to clear the area. I started out too tentative, mostly because I wasn't sure what would happen as i started unhooking lines. The fuel lines can be unhooked from one side and pushed out of the way. You might evaluate the condition of your lines. If they are old and brittle, they might crack if you bend them too much. Also, when the fittings are removed, these lines will leak a couple ounces. It is a good idea to plug them to prevent getting debris in your lines. I used paper towel, but more experienced users may have better suggestions. I also read to remove the break booster vacuum line. I didn't know what it was, so i ignored that instruction. There is a hard plastic line running overtop of the LH valve cover and to a black cylindrical unit (8" in diameter and 3" deep). The black cylinder is the break booster, and the line is the vacuum line. When this is unhooked, you will get a brief hissing, as the tube equalizes to ambient air pressure. Beware, if you try to remove the valve cover without removing the vacuum line, you will likely shear the brittle plastic tube in half. $60 and 3 days later, you'll be prepared to reinstall that line.

2) Before replacing the chain guides, you must first remove the alternator, powersteering pump and their respective mounting brackets. This is a non-trivial task, at least for a newbie. Again, the right tool makes all the difference. For my mount, i'm not sure if this is universal, a number of the mounting bolts were round OD, and a hex inside. Don't waste your time with an allen key. Buy a socket for this job. it looks like a 1 inch piece of a 6mm allen key stuck inside a 3/8" drive socket. you really need the ratchet to put the necessary torque to break some of these bolts loose. If you round out the bolts, you'll have a heck of a time getting the bracket off.

3) For both the alternator and power steering pump, I suggest you take notes as you extract the mounting bolts. Not all are the same length, and it can cost you some time to try to figure out what bolt goes where. In my mind it is worth the extra hour in disassembly to have thorough notes. It might be worth while to have an assistant to take the notes with clean hands, plus this allows you to keep your focus in one place. Also...I read this a little too late, but open the cap on the power steering fluid and extract it with a syringe. This will save you from spilling a pint of PS fluid all over the ground as it dumps from the pump.

4) Extracting the pins from the chain guides is all about the right tools. I searched for an impact / pin puller at 3 different stores with no luck. I read on this forum, suggestions of using a bolt and a series of washers. Before you start, go to the hardware store, get a hardened bolt to fit the threads on the ID of the pivot pin, and more washers than you think you will need (the stack of washers will be taller than the length of your bolt. the idea is that the washers act as a spacer between the bolt head and the exterior of the engine. As you tighten the bolt, it can't be drawn into the threaded ID of the pin because the washers are in compression. The result is tension on the threads that results in the pin extracting. The method that worked best is to fill the bolt shaft with washers except for about 1/8 inch at the tip of the bolt to thread into the pin ~ 2 turns before you start compressing against the washers. Once the washers are compressed, it should take a couple turns and then the pin should start extracting. Then backoff the bolt add another 2 washers or so, and retighten. Repeat until the pin starts to feel loose and can be extracted by hand. Before you do this, I would start by screwing the bolt into the pin as far as it will go by hand. this way you know how far you can thread it before bottoming out the screw. If you bottom out the bolt into the pin...one possible outcome is that you torque the head of the bolt off, even worse if it shears flush with the face of the pivot pin. (nightmare) The best way to avoid that is to use the method briefly described above, and in better detail on some other posts. The location of some of the pins have little flares and lips on the outside of the engine. Consequently, you cant get a washer to sit flush. The result is bending the washers and potentially side force on the pin rather than tension. My solution was to bend some washers in half, then superglue a couple together with a full washer. The number of 1/2 washers should match the depth of the flare on the engine, so that your 1st full washer is sitting flush against the 1/2 washers and the engine. I will post a picture of my bolt and washer setup soon.

5) On pretty much every post regarding the timing chain, there is reference to DIY instruction: http://www.peachparts.com/Wikka/M117TimingChain .
USE IT!!! Read it, print it, highlight important stuff, and then re-read it. The most important piece of information that I overlooked was clamping the timing chain with vice grips in two places (as it goes into the engine...the new chain, and as it comes out from the crankshaft...old chain). This will maintain the relationship between your RH and LH cam cogs with one another and with the crankshaft. It takes a little while to go 1/4 of a turn at a time, but will save you hours as compared to the outcome if you jump some links. As a quick sidebar...as you rotate the engine using your 27mm socket on the crankshaft, the RH and LH cams will have a tendency to jump. As I understand it, this is caused by the cams depressing the springs to open the valves. Once that cam lobe is off center of the rocker, the spring force is strong enough to force the cam shaft (and sprocket) to rotate. In my opinion, the strongest hands won't keep the chain meshed with the sprocket, which is why the vice grips idea shown in the DIY guide is brilliant.

As a quick recap, I would say for a newbie, you could replace the oiler clips, chain guides, and timing chain all at once in a weekend. It would be best to have at least 1 helper. Avoid the mistakes that I made, and you could potentially cut the process down to 1 day (it took me 3 weekends).

My new motto is anything is possible with the right tools. Here are some tools that I highly recommend:
*6mm hex head for 3/8" drive rachet
*Telescoping magnet...life saver on many many occassions
*telescoping mirror
*grabber (spring loaded plunger that drives 3 or 4 metal fingers through a tube, useful for picking up small pieces).
*Torque wrench...these are kind of expensive, so i almost didn't buy it. It was a great purchase...and if you take care of it, it'll last a lifetime.

Again, thanks to the support and guidance on this site. And good luck to those of you preparing for this project.
Justin
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