603 timing chain, missing a link ! - PeachParts Mercedes-Benz Forum

scottmcphee · #1 11-15-2009, 10:27 AM

I went pale and almost panicked when I saw this:

603 timing chain, missing a link !-img_9711.jpg

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First thing I see with valve cover off is this beauty! A missing link segment....

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Thank goodness timing chains are doubled. Ironically, I bought a new chain and link this summer thinking it would make a nice 200K mile gift to the car. Call it premonition maybe. Come to think of it, in last couple months I have noticed a new light "tick" sound, fades in and out. I bet this is why. Been driving hundreds of miles with it. Do I drive it or tow it to the shop?

Last week, my front crank seal starts bleeding. (Hmmm... related?) Anyway, a job I don't want to tackle, so I booked an appointment for Thursday with my indie to get that done. When I was making the appointment we yacked about doing the chain as well, I'd supply it. He asked how many miles on car, and said for sure do the chain. But I was second guessing, reading all the "change only if stretched" advice on this forum. So I thought I'd check this weekend let the old 4 degree rule decide.

OK stretch aside, I think it's time to change this puppy.

Close inspection shows every other tooth on the front-side row of the double sprocket is starting to wear. It's hard to tell from the photo, but the wear is not severe. These teeth are not rubbed down to a tell-tale "thinness" that dictates replacement. The rear-side row of the sprocket is perfect.

I compared to a spare/used sprocket grabbed off my parts car and see that it's teeth are nice normal half moon shaped dips. But that sprocket shows face-wear. Links have rubbed their image onto the front-most flat side of the sprocket. As if the cam was thrust too far forward causing the sprocket to hang out further than other guiding and positioning forces on the chain. The front side of the sprocket, teeth lack a bevelled-in shaping on their sides at the peak. Those teeth look flush / flat on that side of the sprocket. Is this face wear common?

Now the questions:

So for my car, do I replace the cam sprocket too?

Is my spare usable if I were to file a bevel back onto those tips... Or is that just stupid and inviting too much side-side lash -- use new part only?

My deeper fear: If the cam sprocket is starting to show wear on every other tooth then its gear mates on the IP and down below, probably are too. And what about those guide rails? Doing all would push beyond my willingne$$. The killer is this engine in all other respects, and yes its #14 head, is a (knock on wood) top performer.

Diesel911 · #2 11-15-2009, 11:43 AM

Sprockets:
If the Camshaft Gear is worn unevenly the New Chain is goning to try to strech to fit the longr spaces in the Ok Gear teeth.

What is not being mentiond is that the Drive Gear on the Cranks Shaft is smaller and is thei one that is pulling everthing else. To Me a smaller Gear that does more work should be worn more than the Camshaft Gear. The exception might be if it is made of some different alloy of metal (and we would not know that)
So my if it were me I would replace it along with the Camshaft Gear. I not I would be sure to inspect it closely

Diesel911 · #3 11-15-2009, 11:45 AM

If you have a used Engine with good Gears I guess you could swap them.

Billybob · #4 11-15-2009, 02:05 PM

Replace the chain of course; I would replace the cam sprocket with a good used one or a new one as I recall the sprocket is about $40. You should check the cylinder head chain guide for wear anyway and replace if needed, the longer banana shaped guide according to the 602/3 FSM requires the timing case cover removal the change. I’ve only done it with the cover off and don’t know if it could possibly be done with the cover in place.

The timing device sprocket can be inspected by pulling the vacuum pump recommended when R&R the timing chain any way.

The crank sprocket would be a major undertaking to just inspect it very much, you may be able to see some of it if you remove the side cover on the oil pan but you won’t get to look closely at it unless you’ve got a scope or camera in on it. To replace it requires removing the engine essentially, the oil pan and the timing case cover have to be removed, oil pump chain removed, and timing chain and then it can be pulled from the crank. Even then care has to be taken to get the timing cover to correctly seal its top edge to the cylinder head; otherwise the head needs to be re-gasketed.

scottmcphee · #5 11-15-2009, 02:44 PM

Even / odd.. if wear is showing on every other tooth on cam shaft - who can tell me if this translates to every tooth or every other tooth on the crank and IP timing sprockets as well? What's the ratio..

If it's every other tooth on *every* sprocket then I think I'm going to replace the cam sprocket, because it's easy.. with a new part. Inspect the IP timing sprocket because that's easy, and replace if whacked but leave the crank sprocket alone - unless my indie can use a scope to get a visual snaked through the oil side-pan and we see that it's a mess.

Theory being with only every other tooth worn a bit on just half of the chain is going give the chain good enough even grip and should settle well enough that it won't stretch "on one half side" or cause continued damage to sprockets. It's a theory anyway.

sasquatchgeoff · #6 11-15-2009, 02:44 PM

WOW - I would be looking for that other piece of chain in the chain gallery somewhere or maybe even in the oil pan - I most certainly would have gotten pale myself.

The ticking is probably not related - I suspect bucket tappet lifter wear for that symptom.

scottmcphee · #7 11-15-2009, 02:47 PM

Quote:

Originally Posted by sasquatchgeoff

WOW - I would be looking for that other piece of chain in the chain gallery somewhere or maybe even in the oil pan - I most certainly would have gotten pale myself.

The ticking is probably not related - I suspect bucket tappet lifter wear for that symptom.

That was my thinking, and an oil change to different brand quelled the ticking for quite a while. So I didn't worry too much about that tick.

Tells me this timing chain thing would have been a silent killer... if left for ??? how long nobody knows.

I'll see what a magnet can find in the oil pan.

Billybob · #8 11-15-2009, 04:59 PM

Quote:

Originally Posted by sasquatchgeoff

WOW - I would be looking for that other piece of chain in the chain gallery somewhere or maybe even in the oil pan - I most certainly would have gotten pale myself.

The ticking is probably not related - I suspect bucket tappet lifter wear for that symptom.

It might be interesting for sure! It seems inconceivable that the missing link connecting plate could somehow become disconnected at both its ends and come completely loose from where it should be inside of the two adjacent outer links though.

Perhaps a manufacturing defect that somehow made it past quality control back then, nowadays virtually impossible with computerized integrated QC with cameras and sensors for missing parts like in this case not to be detected. The other possibility is a replacement chain where the installer dropped the part when handling it and just said “fork it!” and put things together without the lost part, thinking who would ever know! A close examination of the remaining parts of that link may reveal something.

It is truly fortunate that it was ever seen and noticed, had it been it any other position when the OP removed the valve cover it likely would never had been seen or noticed.

With regard to the “ticking sound” I would not be at all surprised if this chain was not making some condition specific sound/s. Hopefully it will be making a recognizable sound prior to replacing this chain/sprocket combo and if said recognizable sound/s are absent after the chain/spocket-ectomy you could logically support such a conclusion.

Billybob · #9 11-15-2009, 05:29 PM

There is an updated cam sprocket bolt for all 602/3 engines also!

sasquatchgeoff · #10 11-15-2009, 05:43 PM

Making sure the rivet ends are properly swedged is a critical aspect of installing a new chain. Otherwise the rivet plate can easily loosen and fall off, which appears to be what happened in your chaincase. I would be willing to bet that the loose rivet plate is in the oil pan or some nook or cranny on the way down.

On the 601,602, & 603 series, older chains had a "clip" style connecting ("master") link that is no longer available, where the new chains have a riveted style connecting link. The old style links have grooves in the pins where a retainer clip snaps onto the pins retaining the rivet plate. New style rivet pins are smooth and must be properly riveted with a special MB tool.

scottmcphee · #11 11-15-2009, 05:57 PM

I recall reading there's an updated cam sprocket bolt somewhere, but thanks for reminding me, I'll get one of those too.

I have a new MB chain, and new link requiring tool to join.

You bet I'm asking for all removed parts returned to owner, for close inspection of this missing link mystery. If this fail is not near the previous joining / master link.. then, Billybob, you're right, it's a real head scratcher and just maybe an original QC miss. Can you imagine driving 200K miles on a half-a-chain!?

If I find the piece in the pan it might reveal what caused its demise.

I'm pretty sure PO did not do a timing chain - all service records eleven years back and at that time he took the car with only 40K on it... so.. pretty sure its the original chain.

If there is no evidence there was ever a link on the chain there then I'm not too worried about fixing up all the sprockets... they'll continue to serve well with a real chain probably for another 200K.

scottmcphee · #12 11-15-2009, 06:08 PM

Oh, and let this be a reminder / lesson about "5 degrees of stretch" as your only rule to change a chain!

When you're in there lining up the cam mark to compute the difference, take the time and rotate the crank while looking the whole length of the chain and look at every tooth on the cam sprocket.

Billybob · #13 11-15-2009, 06:17 PM

Quote:

Originally Posted by sasquatchgeoff

Making sure the rivet ends are properly swedged is a critical aspect of installing a new chain. Otherwise the rivet plate can easily loosen and fall off, which appears to be what happened in your chaincase. I would be willing to bet that the loose rivet plate is in the oil pan or some nook or cranny on the way down.

“come completely loose from where it should be inside of the two adjacent outer links “

This missing part could not have "fallen off", the adjacent link's plates are outward of the position of the missing part and in fact the swedged pin ends appear to be holding the adjacent link's outer plates still in place!

I'll bet that if the missing part is ever found it either was never installed (dropped accidentally into the chain chase) or by some unimaginable freak both ends had to have been completely destroyed to allow that part installed in that position to somehow leave that position.

Billybob · #14 11-15-2009, 06:40 PM

Quote:

Originally Posted by scottmcphee

Can you imagine driving 200K miles on a half-a-chain!?

In no way arguing, but it's actually four plates to that particular chain link so you have about 3/4ths strength of a chain running. Had it been either adjacent link which has three plates with one missing it would be at 2/3rds strength it would not seem that it could have possibly lasted nearly so long. Very impressive none the less when you factor in 200K miles! I have an 87 TD in very good condition very well maintained which suffered an original timing chain failure at just a hair over 200K so it’s hard to know what causes things to happen sometimes, I would never imagined that there would be instances of a “missing” connector plate from an otherwise complete chain. You now I’ll be carefully inspecting every chain I see now!

But it clearly points to the redundancy value engineered into the design of the double row chain! Undoubtedly a lesson learned by MB as they started building more powerful higher torquing engines. The early 380 gas engines used a single row chain and are famous for its failure! Good Luck!

sasquatchgeoff · #15 11-15-2009, 07:33 PM

Quote:

Originally Posted by Billybob

“come completely loose from where it should be inside of the two adjacent outer links “

This missing part could not have "fallen off", the adjacent link's plates are outward of the position of the missing part and in fact the swedged pin ends appear to be holding the adjacent link's outer plates still in place!

I'll bet that if the missing part is ever found it either was never installed (dropped accidentally into the chain chase) or by some unimaginable freak both ends had to have been completely destroyed to allow that part installed in that position to somehow leave that position.

After re-examining the photo, I am inclined to think that the rivet plate a. was mis-installed on the outside of the two adjacent plates, when it should have been inside (note the distortion of the adjacent plates towards the outside of the chain) and somehow fell off; or b. was never installed in the first place due to loss or idiocy.

It is important to note whether this chain was "old style" (with the retainer-clip "master link") or the new style. scottmcphee, do the pins have grooves on the ends that are missing the rivet plate?

I find it extremely difficult to believe that this chain left the factory as such.