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1981 380sl
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172 Posts
Discussion Starter #61
It is difficult to measure very accurately, did 8 or 10 measurements with the tensioner in and calculated the average. Get the closest offset to that number. The chain is expected to stretch 2 degrees during the first 25,000 km..
Thanks for the info, hchaugl. If I do install offset keys, should I install them to retard or advance the cams relative to the crank, given that the harmonic balancer reads 8 degrees past the 0 when the cams are aligned?

According to section 05-215 of the manual, "An offset of the Woodruff key to the right (in the direction of driving results in the earlier commencement of opening, while an offset to the left results in a later commencement of opening."

However, I'm still not sure whether I want the valves to open earlier or later? (I'm assuming its earlier, but I'd like to know for sure before I screw things up even more.) :grin

BTW, I was wondering if you or anyone else happened to know how long the double chain on a 380sl is when it's new, since I'd like to measure my old one to determine whether it was stretched and, if so, by how much?
 

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1981 380sl
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Discussion Starter #63
Rowdie,

Thanks very much for posting the URL for the thread on worn sprockets. I have to admit that I was hesitant to change my sprockets after my Indy told me not to, even though experts here advised me to. But that thread convinced me that I should definitely change them, especially before I insert any Woodruff keys, just to see if they reduce the difference between my cams and crank.

Before I replace them, though I was wondering whether tying the chain to the grill would put too much angular strain on it and, if so, how it can be tied to the hood without that strain?
 

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1985 500SL + 2009 GLK (previous 250, 280SL, 230TE, 430 ML)
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In my earlier tutorial I provided some drawings showing how the Woodruff keys changes the camshaft angle.
Imagine that the ballancer is at 0 and the RHS cam needs to be advanced, the offset key will then need to rotate the sprocket anticlockwise when standing in front of the car.

I have seen a couple of references where offset keys had to be used after replacing all the parts. One would expect everything to line up perfectly as when the car was new, but the distributor and crank sprockets may be worn a little.

Mercedes would not need to sell offset keys if everything lined up.

I tied the chain to the hood without any damage.
 

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1984 500SL 107, 2006 E320CDI W211 sport wagon, 2009 320 CLS, 1993 E320 Cabriolet W124
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Philoprof have you had a chance to change the sprockets yet?

This is a very interesting thread as my car has 65,000 miles and runs great, but at some point in the future I may have to do the same job....
 

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1978 450SL
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My 450 SL is at 8* and I too will need to address this job soon.
I am thinking chain wear and cam gear wear go together.
That wear is combined to give us whatever degree of "stretch" shows up at the damper TDC indicator.

Seems to me, as the cam gears wear (get smaller) the chain appears to have stretched at the TDC indicator.
Cam gear wear may actually be a larger factor than chain wear.
A new chain on worn gears could still indicate a "stretch".
I know their are other gears in the assembly but these 2 cam gears are easy to get to.

What do you think.
 

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Outstanding Contributor
450slc5.0cab 280sl5sp 280se4.5 500seAMG +250seStkW108 350sl4spdX3 500secEuro
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My 450 SL is at 8* and I too will need to address this job soon.
I am thinking chain wear and cam gear wear go together.
That wear is combined to give us whatever degree of "stretch" shows up at the damper TDC indicator.

Seems to me, as the cam gears wear (get smaller) the chain appears to have stretched at the TDC indicator.
Cam gear wear may actually be a larger factor than chain wear.
A new chain on worn gears could still indicate a "stretch".
I know their are other gears in the assembly but these 2 cam gears are easy to get to.

What do you think.
+1. Exactly my thinking.

strange that everything lines up except the harmonic balancer though.
 

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63 MF 1100, 72 350SL, 85 380SL, 99 S600, 05 Ford F-350, 09 C300, 10 Boxster 987, 12 GL450
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+1. Exactly my thinking.

strange that everything lines up except the harmonic balancer though.
The metal in a timing chain does not "stretch" - the pins and inside of the rollers wear, increasing the gap which effectively lengthens the chain. This can be up to .010 inch per link before catastrophic failure. A full inch in a 100 link chain.

The wear on a cam gear might be up to 5% of the tooth before it becomes obvious that the gear needs replacing - the tooth will look deformed at this point. This wear has far less effect than the cumulative wear on the chain links.

With a new chain, if both cam marks line up, there is no significant wear on the cam sprockets and the heads have not been significantly milled. The offset keys are used to compensate for head milling which will change the timing between the cam sprockets and between the cam sprockets and crank sprocket. Milling each head will reduce the chain length between the RH cam sprocket (viewed from the front) and the crank sprocket and also the chain length between the two cam sprockets. For example - you may have to use a 2 degree key on the right and a 4 degree key on the left to compensate for the milled heads. Offset keys should not be used to compensate for chain wear - replace the chain instead.

If the cam sprockets have significant wear and need replacing, the crank sprocket should also be replaced. The crank sprocket should wear twice as fast as the cam sprockets - all else being equal. The only reason I have heard of for replacing a cam sprocket (baring lubrication failure) was tooth breakage caused by a slapping chain on the left cam or damage from chain breakage.

It appears that there is no reason to replace the cam sprockets in this case or use offset keys since both cam marks lined up with the new chain. The discrepancy in the harmonic balancer index is inconsistent which indicates a procedural problem, not a mechanical one. Unless consistent and sufficient torque is applied to the crank bolt while turning the engine, the backlash from the gear train and tensioner will cause false readings.
 

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1986 560SL: '84 500SL: '84 280SL 5 speed: other 107s
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Philoprof have you had a chance to change the sprockets yet?

This is a very interesting thread as my car has 65,000 miles and runs great, but at some point in the future I may have to do the same job....
It is age and heat cycles that cause the guides to become brittle and break. You should at least pull the covers and check them.
 

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1981 380sl
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Discussion Starter #70 (Edited)
Philoprof have you had a chance to change the sprockets yet?
Sorry for the delay getting back to everyone, but I didn't have time to work on the car until yesterday when I changed the cam sprockets, as many people suggested. Changing the right hand (passenger side) cam sprocket, after removing the tensioner, was fairly easy and definitely reduced the discrepancy between the cams and the balancer, evidently because the teeth on that cam were considerably worn.

OTOH, I apparently skipped a tooth when I changed the cam on the LH sprocket, since that cam was then app. 15-18 degrees behind wear it should have been. So, I removed the sprocket from the cam, used a vice-grip on the cam's shaft to rotate it to its proper position (i.e., so that the line on it corresponded to the line on its tower), and moved the chain one link over, which caused that cam to be in perfect synch with the other cam, the balancer, and the distributor. So, now I just have to put everything back together and hope that the engine runs and that the clanging sound I was getting is gone.

Another thing that I have to hope is that oil isn't leaking from the tensioner, since I somehow managed to strip a few of the threads from the top hole when I tried to compress the tensioner, even though I used a long bolt on that hole to get it started, as Ausiemerc suggested. However, I forgot that he put a nut on that bolt and used the nut to compress the tensioner. But the lower bolt tightened the tensioner all the way down, and I still managed to use a bolt to tighten the top of the tensioner down, though that bolt won't stop turning when I try to tighten it all the way. So, I have my fingers crossed that I won't have to remove it and tap the hole, heli-coil it, or use some other means to tighten that bolt down.

In summary, I definitely suggest changing the cam sprockets when anyone does this job, even though the job is not as easy as the video and write-ups that Panzerpuff and others made suggest that it is -- at least it wasn't for me. However, I couldn't have done it without those things or the help that people here gave me. So, thanks again to all those people. :)

Respectfully,

Bill
 

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1981 380sl
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Discussion Starter #71
If anyone's still around, I was hoping he could tell me how to prevent the camshafts from rotating when I try to tighten the bolts to 100NM (73 ft-lbs) without using the special MB cam holding wrench -- since I obviously don't t want the chain to skip anywhere, and I couldn't prevent the sprocket from turning by holding it or using vice-grips to hold the cam's shaft.

I'm also hoping that I don't really need that much torque, since I already put the valve cover back on the passenger side after using all my weight to torque the cam bolt to app. 50 ft. lbs., and that seemed like an awful lot to me? In addition, since the bolt spins clockwise with the sprocket, I'm thinking that the loosening force is minimal.

Thanks in advance.
 

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1987 560SL
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I think 50 foot pounds is good to go, that is about what I did. I fastened the chain to the sprocket on both sides with four cable ties and at about 50 foot pounds they started to give. You could do this by feel, as a wheel lugnut is about double that force. I think your logic is sound as even if the cam bolt is finger tight, the sprocket is not going anywhere. I generally pay attention to the MB recommended torques, but after pulling the steering wheel I learned to ignore some of those specs.
 

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1981 380sl
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172 Posts
Discussion Starter #73
Thanks for confirming my suspicion, Panzerpuff. As it turned out, though, I managed to torque the LHS cam bolt to 74 by covering one of its lobes with a shop rag, and using a short handled adjustable wrench to prevent the cam from turning, similar to the way MB suggests holding it with that special wrench.
 

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63 MF 1100, 72 350SL, 85 380SL, 99 S600, 05 Ford F-350, 09 C300, 10 Boxster 987, 12 GL450
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Easy way is to partially tighten, install chain, keep crank from rotating with bar and socket and torque cam bolts to spec. No - the chain won't break! Cam lobes are delicate creatures - nick or scratch and you will probably wind up buying a new cam. Loctite blue or new cam bolts recommended.
 

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1981 380sl
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Discussion Starter #75
Gumpy,

I put a shop rag on the cam and held it in place with a wrench that had toothless grips, so that I wouldn't damage it. However, I did notice that one or two of the lobes on the RH cam had some light scratches, which may have been caused by the loose oiler tube on that side. Since the scratches aren't very deep and their rockers are smooth, I was wondering whether I should sand the scratches off with, say, a 1500 grit sand paper or just leave them alone?
 

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Leave them alone! The cam itself is a relatively soft steel designed to withstand torsional stresses - the cam actually twists a slight amount under heavy angular acceleration. The lobes are ground and then heat and/or chemically treated to produce a very hard surface. I do not know what process MB uses on their cams, but the hard surface layer is usually only 20 - 50 microns thick, depending on the process used. Heat treating gives a deeper layer and chemical treatment gives a harder surface.

If the scratch has not gone through the hardened surface, then the lobe and cap should wear normally. As a rough guide, the finish on a metal surface polished with 400 grit SiC has scratches that run 5 - 10 microns in depth, depending on the paper, pressure and phase of the moon. If you can't catch your fingernail in the scratch/chip, then leave it alone and monitor the wear. Not very scientific, but it would probably cost you more to accurately measure the depth of the scratch, than having the cam reground and rehardened.

Light scratches/grooves on cam lobes are not unusual - chips are deadly!
 

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1981 380sl
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Discussion Starter #78
Speaking of oil, I finally put everything back together and started the car, which ran fine. However, when I turned it off and walker around to the passenger side, I saw oil all over the place. Lo and behold, it was leaking from the tensioner, ironically because the threads I stripped by incorrectly using Ausiemerc's technique to prevent doing that stopped me from tightening the top bolt enough to seal the tensioner. :(

So, now I could use some advice on how to tighten the tensioner down. The first thing that came to mind was to put some JB Weld on an 8mm threaded rod long enough to extend out past the uncompressed tensioner and use an 8mm nut to compress the tensioner, similar to the way Ausiemerc suggested doing that with a londer bolt?

However, I just came across a Loctite product called Form-A Thread:


And a similar Permatex thread repair kit:


So, before I try the JB Weld, I was wondering if any of you have ever used these?
 

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Sorry to hear about that - a sinking feeling.

I can not see the condition of the threads, but if you can get 4 threads that are good, then the bolt will hold. The correct solution is a helicoil insert, but I would try another repair first. The helicoil kit would run about $50, but there is a level of skill required to drill and tap the hole.

Alternate:
First step is to thoroughly clean out the old bolt hole, preferably with compressed air. Next run an 8mm bottoming tap to both recut the damaged threads and extend the threads to the bottom of the hole. Use a quality tap (not a cheap thread chaser from Sears or Harbor Freight), cutting oil/tapping oil and be careful not to apply more than about 10 ft/lbs on the tap holder. If you can't find a bottoming tap, use a standard tap and if it does not cut deep enough, just grind the end to make a bottoming tap.
Next insert a long bolt (use 10.9 grade) until it solidly grips the threads in the hole. Run the bolt down as far as it will go before bottoming. If you can turn it 4 turns past where it first grips, the stud will hold. Carefully measure and mark where the bolt should be cut to leave room for the nut, lock washer and a bit sticking above. Cut and smooth the bolt to make a stud, Clean the whole with MEK, acetone or lacquer thinner and dry with air, Put Loctitie blue on the stud and tighten to 20 - 25 ft/lbs. If you don't have a stud wrench, two nuts tightened against each other will work

If you can not get 4 good threads, then using JB Weld or the Loctite product is required - I have never used the Permatex stuff. Make sure the stud and hole are clean and dry (MEK and air) before applying the product. Be very careful not to let a glob of the stuff go to the bottom of the hole as it will prevent the stud from going all the way down. Let it cure according to the manufacturer's directions and add an overnight. Torque the nut to the same spec as the bolt. (28 ft/lbs dry). This repair should hold and if it doesn't, the helicoil path is still open.

Before you do the stud trick, make absolutely sure that there will be enough clearance to replace the tensioner, get the nut and lockwasher on the stud, and torque the nut to spec. Once the stud has been epoxied into the whole, you will need a good machinist to get your bacon out of the fire if the clearance is not there!
 

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1981 380sl
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Discussion Starter #80
Thanks a lot, Gump. I forgot to ask: will I need a new gasket, regardless of which technique I use?
 
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