I’ve finally had an opportunity to run a couple of tanks of fuel through Marlene since installing her 4º offset woodruff key and bringing her valve events back to spec. The jury is in, and the verdict is that she has much better performance and significantly better fuel economy.

After 200+ miles in-town and 400+highway miles her new highway average is 25.1 mpg (city is about 21.3) . Prior to this, overall highway average was barely 22 mpg and city was somewhere between 20 and 21.5.

Off-idle performance has improved to the point that I no longer have a burning desire to install a manual transmission…my desire is merely smoldering now.

While doing this maintenance, I also took the opportunity to compare the accuracy of both the ‘mark alignment’ and ‘dial indicator’ methods of determining timing chain elongation. I set up my dial indicator and then pulled the engine through and aligned the marks 5 different times comparing the results to the dial indicator. Depending on the angle at which you view the marks and which part of the notch in the cam washer you align with the tower mark there is anywhere from 2º to 6º error in the reading you take from the crank.

IMHO, the mark alignment method is only marginally reliable for determining if you have chain elongation greater than 6 degrees of crank rotation and then it is not an accurate method of determing elongation when considering which offset key to use.

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Never a dull moment at Berry Hill Farm.

"that I no longer have a burning desire to install a manual transmission " ..... Blasphemy !

"aligned the marks 5 different times comparing the results to the dial indicator." ... yet more evidence of your Obsessive/Compulsive behavior.

But have you stuck any Snake oil into that Buick Transmission ? You are clearly recovered from your Staping enough to tackle that... you are playing favorites within your stable.... and you need the garage space getting your Buick up and running will give you .... go ahead and deny that all you want... we know the truth....

edit: I did have O/C backwards.

Perhaps on the 617 engine the crank indicator is harder to read, but on the OM60x engines it's quite accurate. I used the dial gauge method and compared to the crank indicator, and it was DEAD on (within half degree) every time. Plenty close enough for a rough check, although you can do the dial gauge too if you want to confirm. Again, I have not attempted this on a 617 engine, but you piqued my curiosity with your findings! I wonder if that's why my 123 has poor fuel economy...? Hmmm!

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Dave
Boise, ID
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As said in my original post, the source of the inaccuracy is in how you align the timing notch on the sprocket cam thrust washer and the mark on the cam bearing tower.

re 123 economy...
I highly recommend returning your cam events to spec on the OM617 engine. The improvement in economy and performance is well worth the effort. The work I did to Marlene has made her a joy to drive in traffic. I'll be doing the same to SWMBOs 300D (260,000 miles) at the end of the next service interval.

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Never a dull moment at Berry Hill Farm.

D'oh, yes, sorry I didn't make myself clear. Yes using the cam tower marks allows for a good bit of error. However with practice it's almost equal accuracy to the micrometer. I did it 5 times in a row and got the same number as the dial indicator method. Here's a photo of the OM603 marks (not lined up in this photo, a few degrees past TDC) :

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Dave
Boise, ID
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I am thinking about getting an offset key for mine. Last time I did a valve adjust 2 months ago, timing was off 5*. Would a new key really help this? Injection timing will still be off time.

If I should, only the 4* or 6.5* keys are ones I can find. Eather way I'm still off time. Would 1* retarded or 1.5* advanced as the valve timing outcome be better for city/highway and occasional comic drag race entry?

IMNSHO, forget offset keys, they're designed to correct problems with GOOD chains, not worn chains. Replace the chain, verify proper cam/crank timing (adjust with offset if required, which it shouldn't), then set IP timing to spec.

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Dave
Boise, ID
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"they're designed to correct problems with GOOD chains, not worn chains. "

Gsxr, Can you elaborate on that ? Perhaps some reference ? How does the logic run on that ?

My father ran the original chain for 25,000 miles on his 750 Honda which did not have an automatic chain oiler or an enclosed chain. Perhaps you are underestimating what a big double roller chain is capable of doing .... ( The Honda chain was only a single ).

The MBZ FSM for the OM617.95x states that offset keys are available to correct performance complaints. There's absolutely nothing in the documentation that specifies the keys are only for use on good chains.

From the FSM:
"If the (cam) timing requires correction, install an offset Woodruff key or, if the chain is excessively elongated, install a new timing chain."

In addition, the FSM publishes specifications for the amount of acceptable chain elongation in units clocking more than 20,000kM (see graphic). To me, this, along with the fact that MBZ provides four different key offsets, implies that these keys are available for use in economically correcting the routine wear (elongation) of the timing chain as opposed to outright replacement of the component.

There is no stated 'maximum' mileage for the chain nor is there any specification for change intervals as there is for vehicles equipped with Gilmer timing belt cam drives. Once a maximum offset correction of 10° is reached on the OM617, apparently, the chain is 'excessively elongated' and should be replaced.

I have a hard time believing that Mercedes would knowingly and willingly mass produce engines which, with 0kM on them, might possibly have as much as 10° of cam timing variance, expecting their servicing dealers to correct this problem after a performance complaint was received from the customer.

The more plausible (and Teutonic) explanation is that MBZ engineers had arrived at an economical method of accomodating the 'x' factor of new cam chain elongation which is experienced in the first 20,000kM of operation.

Attached Thumbnails

 

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Never a dull moment at Berry Hill Farm.

OK! , OK !, Take it easy Randy.. Most of us believe you ......

Probably not.

Your best bet would buy a one way ticket on Southwest to back to Oklahoma from Austin, Texas. Then, drive your car here, give it to me and fly home.

Please change the oil and vacuum the interior before you head this way.

Seriously, contact me via e-mail and I'll give you all the gory details of how and what I did. And, if you can't get a 4° key and actually need one, I'll get it from my wholesaler for you.

R

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Never a dull moment at Berry Hill Farm.

I, too, would be interested in learning more.

On Randy's point, as they advocate keys up to 10 degrees, that suggests that more than 10 degrees is the replacement point. Key at 10, replace at 14? That's almost a whole sprocket tooth (18 degrees)!

Guys - uh - first, let's clear up something. The top quarter inch of that page got chopped off with one teeny tiny detail. All those numbers are AT 2mm VALVE LIFT. You should measure nine degrees at 2mm intake life, which means ZERO degrees stretch. Measuring eleven indicates TWO degrees stretch, which is acceptable according to specs.

Now assuming that's clear, you're saying that a chain stretched 3-10 degrees should be adjusted for with an offset key, rather than replaced? Hmmm. An interesting side note: I found something that may indicate a typo in the manual. The EPC describes the four keys as 2, 3, 4, and 5 degree offsets. The manual says 4, 6, 8, and 10 "crankshaft". It also shows a 1.3mm offset for "ten" degrees. It then says one tooth equal 18 degrees. So if 10 degrees is 1.3mm, 18 degrees would be roughly 2.5mm. Now, from memory, I recall the tooth spacing being more than ~2.5mm apart on the cam sprocket...! I wonder if the EPC is correct and the manual is wrong? Or am I just really confused?

Personally I'd roll in a new chain, and use the offset keys only if needed with the new chain. But that's just me. On my 603 engine, a new chain put the timing marks back EXACTLY on spec, zero stretch. Maybe the older timing design had sloppy tolerances? I dunno. Remember the IP timing must be adjusted after you get the crank & cam timed properly.

Finally, my experience is 99% based on OM60x engines. For those, there are NO offset keys, period. The factory manunal & TSB explicitly state that at 4 degrees or more of elongation, the chain is to be replaced. If the elongation is 10 degrees or more, a borescope is required to check the pistons and valves for damage. So on newer engines, MB decided the old procedure was not acceptable. But it seems that on older engines, perhaps you can run the same chain with offset keys until it breaks (either the chain or the engine ).



Regards,

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Dave
Boise, ID
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Maybe the manual is correct - 2 degrees at the cam = 4 degrees at the crank?

I do agree with you, Dave, that changing the chain is the safe thing to do. I'm just intrigued why they would sell such extreme offsets - as pointed out above, that's beyond any conceivable manufacturing tolerance for a new engine.

Has anyone ever come across a new 617 engine with offset keys installed? Probably impossible to learn at this late date.

See, that's what doesn't make sense. Four degrees at the crank is 4 at the crank, period. There are only 2 reference points - crank and cam, you're measuring degrees different between them. Now 4 degrees diff between crank & cam translates into roughly 2 degrees off at the IP, since it's more or less in the middle, but we're not discussing the IP timing and I'll leave that alone for the sake of simplicity at this point. I went and measured the distance between teeth on the sprocket (chain link), and it's about 9.4mm. However we'd need the distance relatlive to the circumference on the two different arcs, one at the key radius, one at the chain radius, to make the numbers in the FSM mean anything. (I was slightly confused until I realized that. )

So, I think the only way to tell if an offset key moves 2-5 degrees (like the EPC says) or 4-10 degrees (like the FSM says), is if we can find someone who has personally done this - AND took notes to determine the difference in crank/cam offset that was obtained with which particular part number of the 4 available offset keys. Sheesh, I think I'd just change the silly chain.

On a side note, my 617 has never had the chain stretch checked. I hope to yank the cover off and find out soon. If it's enough to warrant a new chain, I might pick up one offset key to play with (they're about five bucks wholesale) and put an end to the debate. Sure would like to hear from someone who's BTDT though!

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Dave
Boise, ID
Check out my website photos, documents, and movies!