In the other thread the pictures show #6 piston skirt has similar wear pattern as #1.

There is indication dealer maintained cars were subject to bent rods. This is not a qualification of dealers, rather a suggestion that 603.97s that bent rods received the same care as 603.96s that didn't. My money's still on a design flaw... partially, if not completely.

Sixto
87 300D

Number 6 would be in line with number 1 as far as vibrations go. My thought was that the flywheel and torque converter act as a defacto damper. This seems to be the case if it is a race against which one will fail first.

Is there a correlation between failure rates and the climate? The prediction would be a higher failure rate in colder climates. If a block heater was not used this would likely obviate dealer maintainence. Are block heaters in general use in fleet vehicles in cold climates?

Ah, but if the rods were irrelevant, the new/updated rods would still be bending. And they are not, or at least are so rare that few if any have ever been reported. What is interesting is that the bending mostly occurs at #1 and #6 cylinders. 'Tis a shame the problem exists at all, us power junkies would love a little more displacement. If I could get an 0.030-over 3.5L then I could badge my car "E36", lol...

:stuart:

Anybody verify that the replacement engines have these length rods? Or even this actual displacement?

;)

Things that make me say: Hmmm.
 

Doing a little research before wrenching, I ran across a couple of interesting things in the FSM:

On the 603 engine, it is mentioned (PR 01.1014/4), in a repair for complained coolant use, that the head gasket can fail. When the gasket has failed into the combustion chamber, it is mentioned that the piston protrusion should be checked, "Possible initial damage to conrod as a result of water hammer.".

It only affects the 124 in this repair, but does IMO support the possibility of hydrolock damage to the conrod due to coolant or oil in the combustion chamber.

Excellent point -- if you aren't an experienced diesel tech (I am not) you might not think to check for conrod damage from a simple bad head gasket.

Injectors on #1 and #6
 

I just converted my 93 300sd to Elsbett SVO/WVO system. When I rebuilt the injectors, the injector nozzles at the front and back of the engine (1&6) would not come out. The others fell out on disassembly of the injector body. Soaked in brake parts cleaner and then came out with some tapping. They were stuck because of black deposits/gunk between nozzle body and injector body. I was also amazed to see the amount of black oily sludge in the crossover pipe, etc. 1/8 inch, some of it hard. I am guessing some of this is coming through pcv valve. Don't know if that is typical or what with these engines?:eek:

Yep, the crud in the intake is normal, thanks to the EGR soot mixing with the PCV vapors. Don't spend too much time cleaning it out, it will just come back, but scrape off the major deposits before re-installing.

The only way to eliminate the buildup is to disable the EGR. But this isn't easy... it requires either fooling the computer into thinking the EGR is still working, or converting to a pressure-operated turbo wastegate instead of the computer-controlled, vacuum-operated, reverse-Polish wastegate that is used on your 603.971 engine.

:stuart:

Did I read correct in post 133, MB shortened the rod when increasing the stroke on this motor? :confused: Whenever I've helped assembled stroker motors (at least in domestic realm) I've always been taught you want longer rods that are used to have a better rod ratio. Rod length divided by stroke.

i.e.
302 Ford (4" bore/3" stroke/5.09" rod) -> 331 Ford (4.03" bore/3.25" stroke/5.4" rod)
351W Ford (4" bore/3.5" stroke/5.95" rod) -> 408 Ford (4.03" bore/4" stroke/6.2" rod)



PERHAPS the shorter rod was used to keep the piston still within the cylinder? :confused: This is a common issue on Gen III GM strokers past 3.75" (stock is 3.62") as the length of the cylinder bore is shorter due to deck height limitations. With strokes in the 3.85-4.25" area, these motors typically have very high oil consumption (wrist pin intersects oil control ring, necessitating an "oil support ring" yet still has oil issues) and are not really recommended for daily use.

The 427 LS7 block is an exception as the cylinder length was increased by around 0.5" on that block to support the 4" stroke (and to be reliable to 100k miles). NOW this motor does feature pistons with shorter skirts also! ALSO the rods were shortened slightly... around 0.3" Perhaps to keep it all packed within the family's deck height limitations?

GM added 0.38" to the stroke (and around 0.5" to the cylinder), how much did MB add? MB did add about 0.31" to the cylinder bore length

3.0L rod is ~5.87"
3.5L rod is ~5.71"

Does anyone have pictures of the 3.5L piston versus the 3.0L? Maybe the damned skirt of the piston dangles too far out of the bore? With this being ever-so-slightly too far out, it could aggravate borderline rods into failure. :confused:

With too long of stroke you get PISTON ROCK at BDC



That's my ramble for the thread. :shrug:

this is an excellent point HMX. especially in an inline motor. perhaps MB decided that the piston design couldn't be altered and maintain integrity, so they shortened the rod instead. insufficient R/S ratio could load the side of the skirt as well. HMMMMM

It seems to me fairly obvious: this engine should not have been bored nor stroked.

The additional bore eliminated the water-jacket between the bores: not good.

The additional stroke caused the wrist-pin to be moved lower on the piston and the rods to be shortened for clearance issues: not good.

It makes sense to try and develop more power and at lower RPM, especially in an IDI diesel, for emissions and fuel-efficiency reasons. However, this really required a new block, as modifying the 603 took away its reliability and longevity.

They're probably quite happy that this engine was a North American engine only, saved them some embarassment in the rest of the world.

I do have a couple of headless 603s in my shop, the 3.5L is for sale cheap if someone needs a useable engine or even a rebuildable core, ... Anyway, the point is that the 3.0L engine has 256,000miles, and you can see all of the crosshatching in the bores. Beautiful. The 3.5L has 237,000miles, and there are scuffs in all cylinders, not as beautiful. Both were good running engines, but you can see that the 3.5L is not going to last as long as the 3.0, just because there will be more cylinder wear. At least, the 3.5L will be expected to use more oil through its mature mileage.

What Mercedes-Benz Engineers needed to do since Marketing runs the show there, is unknown to us at this point. Most of us would like to have the 603.96x continue with the re-designed head, and adding an aftercooler, a multi-valve head, ... VGT, ... a 606? The 3.5L can be a good engine, but IMO never as durable as the 3.0L.

Pal of mine who posts here from time to time has about 425k on his 3.0L, head was off about 18 months ago for gasket and crack repair. Other wise has low oil consumption for what it is... 1 quart in around 1500 miles. I've only seen a few HIGH mile Diesel vehicles. 350K and greater, most have clapped out interiors, bad front ends, trans fails, no AC, etc... and that's how they meet their maker.



Nevertheless, have you measured the compression height (wrist pin location) between the 3.0L and the 3.5L? Disregard the diameter of the piston for this. Then we can make a better assessment of what was done to the bottom end I'd imagine once we have all measurements. Maybe the piston was redesigned, maybe not. Doesn't sound like it.

I'm not that great with math so some of you other guys will have to figure that part out... and leave the excessive beer consumption to me for ideas.

Cheap parts / bad engineering .... :D

So am I correct when I state that the rod bender failure mode is gradually increasing oil consumption and smoke up until the engine is consuming a quart of oil every 250 miles or so?

I have a local member that is interested in having me rebuild his rod bender. He told me that it is currently consuming about 1 quart every 3000 miles, but he wanted to have it rebuilt so that it did not blow up on him in the middle of a long trip. I told him that it sounded like his engine has many more miles left in it, and I did not think there was reason to rebuild it now.

Any input from the rod bender gurus?

I have never heard of one blowing up. They simply consume more and more oil and miss at idle. You gave him excellent advice. He should simply drive it and keep good quality oil in it and keep it changed regularly and can probably get many more miles and perhaps years out of it.

350 sd /sdl
 

I agree with t walgamuth.
Just keep the oil changed ......
FYI..........

Check the play in the turbo. if its a little too much side to side ..it may be time for turbo seals.... It can blow a lot of oil through there....

using a quart every three thousand miles is not even any indication of any bending on the rods imho.....just normal wear, quite likely.

Since well maintained fleet engines supposedly suffered much less (at all?) from this my suggestion would be to make sure the engine is kept in such prime condition so that it starts immediately with as little chaotic initial running as possible. In cold climates that would probably mean the addition of a block warmer. Also, do not let a shut-off valve problem persist for any length of time at all (again, chaotic running behavior).

There are lots of this engines (603.971) in Europe, too.
And it is strange, but they don't seem to bend rods like the ones in America...
I have one with 214000 miles and the engine is still very good.

Mercedes S350 turbodiesel (engine 603.971):

http://img367.imageshack.us/img367/4...50td049kf8.jpg

http://img367.imageshack.us/img367/5...50td053dr2.jpg

http://img147.imageshack.us/img147/7...50td014ow0.jpg

http://img367.imageshack.us/img367/1...14902qfjx6.jpg

http://img147.imageshack.us/img147/5...cado002yv9.jpg

http://img183.imageshack.us/img183/6...14928dcqn7.jpg

http://img367.imageshack.us/img367/2...cado001cd0.jpg




Engine 3.0L (I will try to find a better picture):

http://www.peachparts.com/shopforum/...5&d=1218285690

In my opinion the damage occurs during chaotic running. The 3.0 liter version of the engine shows the damage by the frequent failures of the serpentine belt tensioner. There is a huge amount of stress on engine components during this behavior. The number one and number six cylinders would be most damaged -- the flywheel/clutch/torque-converter acts as a de-facto damper at one end leaving the number one cylinder to absorb the shocks. Over time this can easily lead to rod bending.

People, do some research on how sensitive stroker motors, in particular the rods (because of the angles involved), are to damage from misfiring. There is a huge data set out there from motors that illustrate this damage and those that do not.

People want to blame Mercedes engineers for this. I don't think that is fair at all. The engineers must assume the owner maintains the engine properly and that includes the responsibility for assuring that it starts and stops quickly. There is no way for them to anticipate the "ingenious" methods of abuse.

Hey! That's my engine! :) Some better pics of a 3.0L are below. More are here.

http://www.w124performance.com/image...ent/clean5.jpg

http://www.w124performance.com/image...ent/clean8.jpg

:stuart:

That is correct. Normal consumption for a good 60x engine is one quart per 4000-6000 miles (at least with good Group IV/V synthetics, that don't shear down after 3-5kmi... both my 60x engines are in the 4-6kmi per quart range with Delvac-1).



3000 miles per quart ain't bad. What brand & viscosity oil is he using? It will not "blow up" mid-trip, if that's his concern, there's nothing to worry about. It's a much more gradual failure. An old-time German mechanic I talked to about this issue told me the proactive solution is to yank the engine and replace the rods (with the updated style) BEFORE the bottom end is ovaled out. This should prevent it from happening. The question is, did you catch it in time...? And does he want to spend the $$$ when the engine is ok so far?

Personally, if that were my car, and I was planning to keep it long term... I'd tear it down, replace the rods, bearings, all chain rails, and timing chain (if original). Could be about $2k in parts plus dozens of hours of DIY labor. But I wouldn't touch the cylinder bores unless there was damage, or they were out of spec.

If he's not going to keep it more than a few years, just drive it and don't worry about it until oil consumption changes dramatically (i.e., goes to 1500 miles per quart).

:nuke:

Does anyone do a leakdown on these engines before pulling them apart?

I think an important part of this situation is querying other areas of the world and situations where these stroked engines were used. Do/did they suffer the same fate? I suspect it is an issue of preventive maintainance that minimizes periods of engine operation with chaotic combustion events such as cold starts and running on due to shutoff valve issues.

I think the high failure rate of the belt tensioner parts is how the same situation is played out with the 3.0, except that the geometry of the crank/rods is better with respect to side forces.

Disagree
 

This was/is a world wide problem.

There where design, engineering, metallurgy, and other issues involved.

Even the most aggressive preventive maintenance did not stop or alter the failure.

Machine shop that just did the head I sold to Hitman has a 350SDL in the shop with a bent rod.

I sat with the machine shop owner and shared with him about what I've learned here in regard to the rod benders. He had no idea (he's an excellent machinist, but not a Mercedes specialist) and was most appreciative.

Worldwide failure data to back this up?

I think the major problem is that computer modeling cannot predict chaotic events -- by definition.

The hypothesis I put forth explains the failures in the 350 SDL. Moreover it also explains high failure rates of components in the 603.961.

Moreover, it explains why the failure is seen predominantly in one cylinder bore. [Destructive harmonics/flexing in chaotic combustion of a straight six will affect the end throws most greatly -- cylinder six has a large defacto energy dissipator adjacent to it plus typical crankshaft design normally reinforces the area at the rear. Cylinder one is most vulnerable.]

Moreover, it explains why redesigning the rod did not completely solve the problem.

Answer
 

Search the forum, I will not do your homework for you.

This issue has been covered to an insane / nauseating level.

The problem is predominantly in two cylinder bores, not one, it nearly always is cylinders 1 and 6. Whatever the cause (harmonics, EGR soot, bad fuel, sun spots, etc) the rods were still too weak.



Redesigning the rod did completely solve the problem. There has been no documented failures, to my knowledge, of an engine with the new/updated rods later bending those new/updated rods.

:nuke:

"This was/is a world wide problem.

There where design, engineering, metallurgy, and other issues involved.

Even the most aggressive preventive maintenance did not stop or alter the failure. "

Kevin,
Design & metallurgy problems are also engineering problems.
The simple fact is that the designers of the rods did not make them strong enough. There was not a sufficiently large design factor to allow for the metallurgical limitations of the rod, this could have been a casting issue, poor data on the shock forces associated with low centane fuel or even wrong yield strength data of the rod material.
Motors are supposed to be designed for a worst case scenario, this wide spread failure shows clearly that had not occurred. MB simply beefed up the rods & the problem went away.

I stand corrected -- my hypothesis welcomes your clarification that it predicts failures even better than supposed.


I can understand the issue with documenting failures. ;)

By virtue of what I do I follow threads on hundreds of different engines. It is common knowledge that merely one instance of detonation with a highly stroked engine can bend a rod such that the engine is inoperable. I do not think this issue is the fault of Mercedes.

Kevin,
The 350 is not a "highly stroked engine". If the failures were very limited, to a few motors that had been extensively modified or if hydro lock was the issue, I would agree. Unless some one has some professional experience & education in design of machine elements they are not in a position to make a qualified judgment. Following motor failures on internet threads does not provide some one with the necessary professional knowledge to make a proper judgment. I would recommend any one wanting to make such judgments to first consult a recognized text on stress analysis & machine design. Some thing like "Design of machine elements" by V.M. Faires. The maths normally gives some grief unless it has been studied well beyond secondary school.
It is likely when MB first had a failure reported it would have been put down to a poor casting. When a flood of failures started to occur as they did, some one would have realized that it wasnt ok to just lengthen the rod a little. It needed a complete re-design.

I disagree -- 8.2mm is a large jump. Certainly there are other engines with much larger strokes, of course.

I just reviewed a part I designed for a BMW straight six M30 3.0 at 80mm stroke, the jump to 86mm lead to the 3.5. The Mercedes engine, also a slant six design, starts out high and goes higher.

A 91 mm stroke in the S54 BMW blocks is pushing it. The stroked crank is retrofitted to the earlier M20 blocks with the same bore spacing.

Thank you. I do longitudinal studies within and between groups analyzing engine designs and families over dozens of manufacturers -- that is how I judge what works and what doesn't. This is how I relate the failure of seemingly disparate components from serially developed engines in the same family and come up with what I regard as the most promising hypothesis in this situation. This is also how I solved an approximately 25 year standing engineering problem with the Porsche 928. The area I studied at the university was theoretical areas of logic and mathematics. My thesis director authored a text on the philosophical foundations of probability theory.


I suspect Mercedes recognized the issue at hand just as Porsche recognized the issue with the 928. Is is more economic to try to strengthen a part being exposed to transient spikes in force than to re-engineer a collection of systems that would ensure and enforce that the engine had minimal periods of chaotic combustion.

Not a problem. Further searching this thread, which I last read about two years ago, yields the assertion that the 603.970 is a USA (North America) only engine. This places the onus back on your shoulders to support your assertion of worldwide failure data.

Thank you.

Wow. I reread this thread and after all this time, still no definitive answer. Amazing.

Jim

Well...
 

You know "Somebody" in Stuttgart knows.
(Betcha there's an MB White Paper on it.)

'US,we'll never be told.

A couple weeks ago I spoke with a customer about an issue with the Ford Kent twin cam (TC) motor -- so now we're going back 40 years. The carrier for the cam chain tensioning gear is often found damaged. The reason why is that it is not designed to resist the forces of the engine being turned backwards.

Is this a design flaw? No.

It is also not a design flaw in the old Golf/Rabbit VW if you use the cam sprocket to rotate the engine and overstress and damage the timing belt.

Do people get away unscathed, often, with this sort of unintended abuse to engine components? Yes, of course.

There are huge amounts of stress imparted to the engine when a diesel fires chaotically. It is easy to neglect the idea that a customer can damage engine components with just one session and that the results will take a long amount of time to manifest themselves.

Blowing out a tire or open differential from heat by over-revving whilst stuck in snow or on ice. This has a more direct or obvious cause and effect relationship.

Putting on an undersize replacement tire and having the car detect this and go into a limp mode. This is an example of enforcing upon an owner protection of the drivetrain. Perhaps Mercedes should have implemented this sort of system when customers unknowingly abused the engine. Other iterations of the Kent engine tolerate the engine being rotated backward before and after the TC design. This still does not make the TC tensioner a design flaw.

Just my opinion, of course.

The best way for an outsider to penetrate this is to examine patents or visit SAE.org and search through journal publications. Often times there are oblique mentions of issues that a given design solves/addresses.

Ford sponsored research at MIT on windage issues with a particular V6. This generated at least three papers. You can bet that the research was not sponsored on a whim.

The 603.970 is a USA (North America) only engine, used in the W126. However the 603.971 was used in both USA and Europe, in the W140. They are essentially identical long blocks, with different exhaust manifolds and injection pumps.

:nuke:

All your examples above relate to either an inept mechanic doing something he ought not, or an inexperienced driver doing something abnormal (i.e., overrevving) which subsequently caused the damage.

On the 3.5L OM603 failures, neither scenario applies, not even remotely. These engines failed in huge quantities (statistically) under normal everyday operating conditions. Your scenarios cited above simply do not apply in this case, not in the slightest. Especially given the OM60x family's heritage of near zero bottom end failures under any circumstances, even when pushed to double or triple their original power output (the Finns routinely do this with 2.5L and 3.0L OM60x engines, with again, almost zero failures). Yet the 3.5L can't even cough up a lousy 148hp/230tq without bending rods? Hmmmmm.

Why can't you accept the probability that the original 3.5L rods were simply too weak? That's what MB came up with as a solution (new, stronger rods) and - gasp - it worked.


:deadhorse:

Wonderful -- so you know for certain that the rod design used in the 603.970 is identical to that used in the 603.971 ?

If we assume that the Mercedes factory documentation in the EPC is accurate, then yes. The connecting rod was updated four times on the 603.970, here are the four part numbers in order:

603-030-19-20 (original rod)
603-030-22-20
603-030-25-20
603-030-32-20
603-030-29-20 (current rod)

The 603.971 has the same supercession sequence except that it started with the #22. It appears the #19 rod was only used on early .970 engines and never the .971 engines. The .970 was used in 1990-91 model years only, the .971 was used from 1992-up.

The footnote on the supercession states "ONLY REPLACEABLE BY THE SET - THE OLD PART MUST NO LONGER BE INSTALLED IN THIS PLACE", meaning MB wants you to install six of the #29 rods any time an older rod fails.

Sorry, I simply disagree.

An inexperienced owner could easily try to start a recalcitrant engine in cold weather and damage it. Simply neglecting to have the proper grade oil could cause this.

I am sorry, I simply disagree. The difficulty is that one needs to identify the underlying causal relationship [shared] between one set of statistical anomalies and another. The earlier and smaller displacement 603.961 has a high rate of tensioner failure. You are also assuming that (say) an induced triple the output with controlled combustion is equivalent to the stress of the spikes found with chaotic combustion.

I just look at data differently, I suppose. ;)

Now THAT I can agree with.

:whistling2:

So, it is clear that the .971 engines DO NOT share the original rod design.

Aside: if you redesign a rod to a pattern with equivalent but redistributed mass it is highly likely that you have altered the dynamic balance qualities.

The first rod, no. But the next three in the sequence were equally bad. MB got it right on the fifth attempt after about 5 years. The .970 engines used bad rod design #'s 1, 2, 3, and 4 before getting the "good" one. The .971 engines used bad rod design #'s 2, 3, and 4 before getting the good one. The "original" design is somewhat irrelevant as the early .971 engines experienced the same failures, at least through mid 1995 model year production, which is roughly when the final rod iteration was released.

The original design is not irrelevant if you are attempting to do a statistical analysis of (purportedly) worldwide data. Correct? Yes, I do look at data a bit differently, don't I ?

Now, I welcome the presentation of worldwide data of .971 engines with the first redesign, i.e. their original equipment at least to a given time in production. My hypothesis predicts that there will be distribution of this particular failure that positively correlates with a given range of cold winter climates (amongst many other possible variables).

Prove the prediction of my hypothesis to be incorrect.

Thank you.

It's YOUR hypothesis. YOU prove it. I am not going to do your work for you, and neither will anyone else.

In the meantime, all you have is a hypothesis: not a proven root cause, nor a fix that is anything different than what has been working for the last 15 years - new rods.

:balloon2: