Do your own research, there is media documentation of the 60% failure rate.

"I cannot understand why people are not paying more attention to the physics behind a failure that dogs these engines to this day. Pay better heed and address the tensioner failures in the here and now."

It is unlikely that you could provide an appropriate explanation using physics for this. It is off topic & so will be ignored.

Your suggestions concerning chaotic combustion has no merit and further more the shock loads involved at cold idle or during shut down are insignificant compared to the load on the rods under full load at maximum torque. Those loads can be as high as several tons.
The stroking of the motor did not require rod lengthening, in fact the rods need to be shorter. Best you do a little geometry. The changing of the location of the rod pin in the piston, lower down, would also reduce the rod length, This will increase lateral component of the forces on the piston though.
Enough data on the proportion of motors that failed out of the number that were imported has been provided to allow some one who claims to have appropriate training in maths to predict easily the outcome of hypothesis testing. Judging by the lack of credible technically competent & and accurate information provided concerning 'chaotic combustion', It is hard to believe that they have anything more than a very basic if any understanding of the topic & there has been nothing presented to show a causal link.
At this stage The most appropriate response to the 'chaotic combustion' explanation is ;

__________________
Grumpy Old Diesel Owners Club group

I no longer question authority, I annoy authority. More effect, less effort....

1967 230-6 auto parts car. rust bucket.
1980 300D now parts car 800k miles
1984 300D 500k miles
1987 250td 160k miles English import
2001 jeep turbo diesel 130k miles
1998 jeep tdi ~ followed me home. Needs a turbo.
1968 Ford F750 truck. 6-354 diesel conversion.
Other toys ~J.D.,Cat & GM ~ mainly earth moving

Yes, so far I have found anecdotal mention of an anecdotal 40% failure rate and 60% survival rate (survival to what, I do not know). Lumped into that failure rate are a number of different problems. So already I see various aspects of cognitive psychology in action.

Anyone ? Worldwide connecting rod failure data on 603.971 engines with the first set of redesigned rods --?

http://www.epi-eng.com/piston_engine_technology/torsional_excitation_from_piston_engines.htm

Note that when an even fire straight six has chaotic firing patterns the torque reversal peak becomes more pronounced. The article does not come right out and say this but any mechanical engineer worth their salt could glean this. Right? Gosh, when I was in grad school this sort of reasoning ability was expected. [Hint: consider only one cylinder firing when normally all six would in proper order...]

The additional stress of heightened negative and positive torque peaks put out unanticipated stress which is directly transmitted to the crank (hello Mr. Rod) and serpentine belt drive, ergo the belt tensioner is also having to deal with much more rapid and pronounced torque reversals, i.e. shockloads.

Maybe you would be better served by not ignoring the topic. Just a thought. Just a thought.

Yes. Nothing wrong with that.

I gather you are referring to the mismatched Porsche parts. The customer did not misassemble the parts. They came that way from an engine with over 100,000 miles on it. The only reason this was caught is because the customer did not have the rods resized in the rebuild of his racing engine and he happened to take a picture during the rebuild. Interestingly, this was the number six rod and so was initially blamed on the high failure rate of that bearing during competition. Alas, it is so easy to jump to conclusions. It is important to carefully examine the data at hand.

I also took the time to mix and match caps and beams from my core engine and presented the measurements. From that small sampling it was easy to demonstrate that potential misalignments were possible such that they would not be noted easily by eye. When the motor was originally run in for a street vehicle the protruding edge of the bearing had time to wear down with no obvious deleterious effects. In a race engine put to full output shortly after rebuild sans resizing of the bore this was disasterous.

The take home point is that I was suspicious of trusting serial numbered items blindly from a company also noted for its engineering prowess.

"Note that when an even fire straight six has chaotic firing patterns the torque reversal peak becomes more pronounced. The article does not come right out and say this but any mechanical engineer worth their salt could glean this. Right? Gosh, when I was in grad school this sort of reasoning ability was expected. [Hint: consider only one cylinder firing when normally all six would in proper order...]

The additional stress of heightened negative and positive torque peaks put out unanticipated stress which is directly transmitted to the crank (hello Mr. Rod) and serpentine belt drive, ergo the belt tensioner is also having to deal with much more rapid torque reversals, i.e. shockloads.

Maybe you would be better served by not ignoring the topic. Just a thought. Just a thought."



Having reviewed your post & link;

We have now gone from chaotic combustion to chaotic firing patterns. 2 completely different things!! Have you now realized that your reference to chaotic combustion was total BS ?!!

There is no author to the article, no peer review, no raw data or details of the actual motors that the data came from. Much skepticism is needed to be attached to any article on a web page of an organization trying to sell something.

The graph for a straight 6 appears strange in that it suggests that the motor is not producing torque when the crank is at 90 deg to TDC, this is the point of greatest leverage. PVT/thermodynamics & combustion theory contradicts this graph.
Best you have your Mech Eng mate go study up on the diesel cycle, in particular combustion & gas expansion. Reputable texts suggest that combustion and so energy conversion to mechanical energy (torque) continues even after the exhaust valve starts to open. This is beyond 120deg when the next cyl has fired and so is providing torque. The negative torque shown does not occur. Not even for a very lean spark ignition engine engine could it be forced to do this in unusual operating conditions except if the exhaust valve opened before 90deg ATDC. This is because the chamber pressure is still greater than the crankcase pressure & so providing energy from expansion.
It would appear that who ever put that graph together must have been asleep when (if) he studied thermodynamics at university.

I suspect what we have here is some one trying to sell an idea for a super light weight balanced motor that does not have sufficient rotational mass to provide appropriate dampening. Probably it has very weak rods.
Aircraft motors are somewhat different from a design criteria to that of a production car motor as weight is of added importance, hence you comments fall flat for a production diesel like the 603.
I hope that some one of the caliber of Brian Carlton will tune in and confirm this.
The belt tensioner is required because of the length of the serp belt & the amount of stretch it undergoes under load from the power steering pump, water pump/fan & alt.
I suspect that I may be commenting to some one with little if any practical knowledge. Pure maths is a long way from professional engineering.

__________________
Grumpy Old Diesel Owners Club group

I no longer question authority, I annoy authority. More effect, less effort....

1967 230-6 auto parts car. rust bucket.
1980 300D now parts car 800k miles
1984 300D 500k miles
1987 250td 160k miles English import
2001 jeep turbo diesel 130k miles
1998 jeep tdi ~ followed me home. Needs a turbo.
1968 Ford F750 truck. 6-354 diesel conversion.
Other toys ~J.D.,Cat & GM ~ mainly earth moving

I do not have the time or desire to relate the possible parsings and valid set theoretical meanings and implications of those terms. Suffice it to say -- you're really grasping at straws and I did attend U.C.S.C.



I feel certain that Mr. Kane would be glad to defend this article. With a wee bit of effort you would have found his resume:

Edit: You might do a bit of further reading there. Jack has some interesting remarks about the first batch of Datsun 240Z straight six engines that arrived sans harmonic balancers.

Kevin,
He sounds too good to be true. Problem is, if you strip away all the hype, he is far from an expert in combustion and basic engine theory & design. Its a pity that the article is technically flawed. There is no citations on the article.
After all only fools believe everything they read on commercial sites on the internet without appropriate citations/peer review.
One can only ask why he has not referenced the article to any work by respected academics in universities.

A common problem with those with a back ground in electrical engineering/soft ware/ maths, many have never studied the appropriate areas of thermodynamics.
I am sure he is a very good electrical/electronic systems engineer & pilot. It sounds like his background is that of an electrician who ventured into systems & software. He has also become a machinist along the way.


No mention of professional association memberships. No mention of the Universities that (if) he has been associated with.

__________________
Grumpy Old Diesel Owners Club group

I no longer question authority, I annoy authority. More effect, less effort....

1967 230-6 auto parts car. rust bucket.
1980 300D now parts car 800k miles
1984 300D 500k miles
1987 250td 160k miles English import
2001 jeep turbo diesel 130k miles
1998 jeep tdi ~ followed me home. Needs a turbo.
1968 Ford F750 truck. 6-354 diesel conversion.
Other toys ~J.D.,Cat & GM ~ mainly earth moving

Page 435. Peer reviewed. Graph is on the top of the page. Concurs with Mr. Kane. Good try.

Yawn.

http://www.ijest.info/docs/IJEST10-02-04-12.pdf

Best you go & look at fig 5 in that article. It shows that at 90deg & other corresponding cross over angles that you have 2 cyl with 30 bar (~440psi) pressure on the pistons. This will give a significant positive torque.
This report discredits your mate Mr Kane's article. I suspect that Kane's article has not undergone proper peer review. Basically its designed for commercial purposes.

I also note this is for a moderate speed DI diesel with around 15:1 compression. This is nothing like a 603 IDI motor. The IDI has a significant effect on smoothing any pulse in the combustion cycle. It is likely that a motor like the 603 would have a pressure characteristic with a slightly lower peak & a much slower taper off as the combustion is controlled by the IDI configuration.

Nice try!!! But you will have to do better than that!!

I have seen that article before as it is part of a study for determining misfiring in DI motors. The motivation for the study was for work with generators. The micro harmonics were suspected to be finding their way into the output of the generator. There was some similar work done with IDI motors but they couldnt get the required strength of harmonics.

It kind of blows another hole in your argument.
You have dug your way ito a hole you cant see out of !!

__________________
Grumpy Old Diesel Owners Club group

I no longer question authority, I annoy authority. More effect, less effort....

1967 230-6 auto parts car. rust bucket.
1980 300D now parts car 800k miles
1984 300D 500k miles
1987 250td 160k miles English import
2001 jeep turbo diesel 130k miles
1998 jeep tdi ~ followed me home. Needs a turbo.
1968 Ford F750 truck. 6-354 diesel conversion.
Other toys ~J.D.,Cat & GM ~ mainly earth moving

If I owned a 3.5 the first thing I would do is get a fuel pressure gauge installed. Then always change fuel filters as soon as there was any evidence the fuel pressure was starting to fall. This in my opinion would be first noticeable on the highway at speed. So the gauge has to be readable in the passenger compartment.

I still retain this crazy unproven theory that as the fuel pressure falls the sequential fuel timing retards a little progressivly down the injection pump elements in relation to the number one fuel element. It may be as simple as the base fuel pressure cannot function as designed with a closed relief valve to moderate all the spikes generated to some extent. Yet in my opinion it is just not the increased turbulance.

Some complex interaction seems to be underway that somehow or other is allowing the number one injection pump element to function better than the others it appears.

Simply expressed. The injection pump is calibrated at a certain feed pressure. If this were not true the calabration of the injection pump being done at a specified fuel supply pressure would not be a serious requirement. It is.

Lower than desired fuel pressure results in increasing the loading in proportion on the number one cylinder. Until someone can disprove it. I also see it as the possible higher wear issue on components of the number one cylinder in the 616 and 617 engines.

The 3.5 just fails easier because the block is weaker structuraly than the 616 and 617. If the block where tougher the number one rod bearing failure of the 3.5 would be the result of low fuel pressure eventually.

If the number one rod bearing is also one of the major failure points on the same block at three liters would also add fuel to the fire. I have not checked up on this.
.
My problem is even if this somehow proves not to be at least a true component or contributing one in failures . It cost next to nothing to eliminate it as a possibility. Plus things like fuel milage and general running are better with proper base pressure always present in the injection pump.

It has already been reported by people that have corrected their fuel pressure from sub standard pressures.. The engine sounds happier on the highway. If the difference between low fuel pressure and normal is audiable to the human ear something is going on of a signifigant nature.

Low pressure can be just a case of leaving the spin on filter on too long. Without a gauge you will never know this otherwise until the gradual obstructing and reduction of pressure become noticable.

You may have driven thousands of miles with sub standard fuel pressure till that point. Now the cars that got their fuel filter changed out at every oil change service at a dealer. As part of a profit centre or close equivelant may have dodged this bullet. The engine is still the same weak design but manages to survive within the designed running load paremeters as a result.

The 616 and 617 is quite a rugged design but still can wear the first cylinders rod bearing down under the right conditions remember. I had considered geting into this in some depth earlier. Yet the difficulty in trying to get the message across to even the 616 owners was and still is difficult.

Even today there are few that give this area serious consideration even with the results of other members in limited numbers. Plus I consider it proven enough that constant proper specified fuel pressure is always much better than sub standard pressures.

The most important of any component I can think of with this fuel pressure issue. When the available pressure in the base of the injection pump falls below the opening pressure of the relief valve. This closes off access to the cigar hose. So all spike issues are retained in the injection pump.

I am aware that some influence will be present from the filters and as far back as the lift pump. There is just far greater dampening possible with the flexiable cigar hose. You can even feel the hammering present in it when the relief valve is open.

If the output valve of the lift pump is intact the buffering of the lift pumps main tensioning spring is not even able to contribute to the loss of the cigar hose. Except when the output valve of the lift pump is open possibly during the charging cycle of the lift pump that occurs once every injection pump revolution. This in itself could make the number one element of the injection pump respond more normally during the spike turbulance chaos.

I am far from certain how much impact all this would be having on the 3.5 liter engine. It is just worthwhile to make sure the fuel pressure is good all the time just in case.

Mr. Kane's article clearly states:


In S. H. Gawande et al, the title of figure 1 clearly states:

The presented torque curve in both Kane and Gawande match well which is not surprising since both authors acknowledge the curve as typical and/or well-known.

You point to figure 5. of actual operating data from a particular engine. As well as differences being anticipated by Kane, it looks to me that they are simply not including rotational inertial torque.

Ok, so now I am gazing down at you in that deep hole you've excavated...

Edit2: While I was working on this reply I took a phone call from someone who explained to me why the data covering the 60%+ early failure rate of .971 rods would not be available despite his first hand knowledge of it.

The weak design of the rods was not the fault of Mercedes engineers which I found heartening. In the cases related of new vehicles there would not have been customer abuse. It is simply a matter now of trusting and believing what this person told me and I can do that.

layback40, you're still down in that hole.

Sure, it's no more the fault of Mercedes engineers than the defective OM603 turbo cylinder head castings. It took MB about 10 years and 5 redesigns before they finally came up with a design robust enough to deal with real-world operating conditions. The difference with the bent rods is that (a) the cost of short-block repair is 5-10x the cost of a head swap, and (b) MB was refusing to acknowledge the bent rods nor accept responsibilty unless forced to.

I still don't get what your proposed solution/repair would be for a 3.5L with original rods.

If I accept the data that indicates weak rods then it follows that, optimally, the rods should be replaced and at the same time the bores can be measured for ovality. I asked if aftermarket companies had pursued making these parts and was told that they had but that Mercedes in some direct or indirect way effectively ended this option. That would be understandable if the rods were marketed as a solution to a failed OEM part which Mercedes did not want further publicized. My suggestion would be to market such a part as a performance upgrade or racing item. It was pointed out that the Finns have published information on such items.

The lack of sound argument being presented hear by Kevin defies belief!!

Mercedes had a problem and eventually solved it. It was under designed rods !!

There is a 5 cylinder version of the 603 3.5, & there are many commercial vans & 4WD's fitted with them, some have done more than 500k miles. Now according to "Kevins Chaos Theory" they should have the "negative torque" problem to a much greater extent (5 cylinder, not 6). These motors are in use all over the place. I have one in the shed for when my 602 is no longer running. They have no history of bending rods. You may need Dr Who to explain that away, maybe its the dialects or flux capacitors or some other cosmic force, maybe magnetic eddies or Brownian motion considerations ? Are you suggesting it could be cured with a Coulter Counter?

"As well as differences being anticipated by Kane, it looks to me that they are simply not including rotational inertial torque. "
It looks to me that you have just shot your & Kane's negative torque proposition in the foot !!

I am done attempting to debate with an ##### (forum rules wont let me use that word).
We have gone from Chaotic Combustion to Chaotic Ignition to Negative Torque to ignoring Rotational Inertial Torque to who knows what. Its time for me to stop being dragged down to an argument based on incompetency and throw away quotes from Google searches as I would then be beaten by experience.

Even the Koreans were able to see the need for the stronger rods when they built the variants to the 603/602. Its a no brainer really.

"My suggestion would be to market such a part as a performance upgrade or racing item."
We now see the basis of what is Kevin's real motivation.~ Let some aftermarket performance mob make the part & charge for it. I guess they could throw in a K&H filter or 2 as well.

Do you have any experience with Mercedes 60x diesels Kevin other than maybe your "cousins best friends little sister's boyfriends mother's neighbor once saw one on the internet"?

"Another very esoteric thing that you can take home from this exercise is how psychological warfare is often conducted through disinformation campaigns. People remember bits and pieces of things that they read or hear and amalgamate them oftentimes into something quite novel -- but incorrect.

I am not saying that malintent is here, by any means, but the effect is clearly observable. Here we have misinformation rather than disinformation. "

Remember saying this?
It may be worth quoting the next time a thread is hoodwinked like this one.

__________________
Grumpy Old Diesel Owners Club group

I no longer question authority, I annoy authority. More effect, less effort....

1967 230-6 auto parts car. rust bucket.
1980 300D now parts car 800k miles
1984 300D 500k miles
1987 250td 160k miles English import
2001 jeep turbo diesel 130k miles
1998 jeep tdi ~ followed me home. Needs a turbo.
1968 Ford F750 truck. 6-354 diesel conversion.
Other toys ~J.D.,Cat & GM ~ mainly earth moving