BC

Kevin - do you think there is an issue with reduced piston oiling because of the oil scraper. Assembling my stuff (from you) , I had a thought about this.

BC

Would the stream go that far up?

cooleyjb

You assumed I knew nothing about fabrication of parts for cars. I gave an example of where your assumption was wrong.


The amount of difference in cranks by Porsche can be measure in 1/8" and greater???
Yes you did. They asked you for a rod and cap that had matching numbers that had incorrect dimensions on the machined surface. You haven't produced anything of the sort.Yet again show me an instance where the matching number rods/caps are mismatched. You are coming up with a wild story to explain something which has no evidence to support it.

I am just asking for some evidence from you to support your hypothesis. So far you haven't. So far the only hard evidence you have given has shown that matching number rods/caps have the correctly machined surfaces.

cooleyjb

You still have provided no proof to support your hypothesis. Anecdotal evidence means nothing.

So until you can show me some actual numerical proof.... I'm done with your hypothesis until you can show me something substantial.

I had absolutely nothing to do with the build of that motor yet again another assumption of yours that is incorrect.

brutus

That is the misalignment ? The .8 mm ? Do you not understand how these rod were made ? Only the machined surfaces after the cap is bolted to the rod are important. What you show are forging variations of two pieces made at different times. They only come together for machining of the big hole in the center and the sides of that hole. And that is when they are numbered as matched parts.

brutus

WTF ? the bearing caps and the rods arrive in bulk . They have never seen each other before ! The machinist bolts the cap to the rod and procedes to machine the big hole for the bearing and cut the outer faces of that hole. As long as that hole is to size how the rest of the rod LOOKS makes no difference at all. If the hole for the bearing had a .8 mm misalignment the rod would not fit on the bearing and that engine would have failed long ago. Porsche only built at most 20 engines for the 928 per day using triple digit numbers there is little chance that two of the same numbered rod caps ended up in someone's hands at the same time so they could mix them up.

Lizard928

Brutus, I would give up as some people just cannot grasp this.

Kevin Johnson

Just to revisit this -- and, Stan, I do apologize for going a bit off topic in a drilled crank thread.

I am quite sure that some people think I am a nutter or insane or just plain rude, perhaps. Some people think I am a fool. Some people find my theories are bullcrap. I think about technical problems all the time; some problems for weeks, months, years. Turning them around and around in my mind.

I put this on hold for a week or two.

My theory is correct -- my belief. I can back up everything I say which is a far sight from my critics.

I suggest the people who feel they know how Porsche 928 connecting rods are manufactured do their homework as I have done. The information is out there but you do have to get off your behind and find it. I make the effort because I take what I do seriously.

Porsche 928 connecting rods are sintered forged and it is the morpohology or formed surface features that allow them to be held in machining fixtures. Just as I said. GKN developed the process for the 928 rods in the mid 1970s. Production was taken over by Krebsoege and Thyssen Umformtechnik. There is an article you can purchase from Elsevier Ltd. for $31.00 that discusses this.

The shifting to one side of mold morphology is a clear indicator that the rod and cap came from a different initial forging or were machined at different times in a fixture with altered settings. Since the rod in question was bracketed by correctly machined/aligned rod and cap pairs this leads to the mix up scenario at either Krebsoege or Porsche.

Two rods sets with the same serial number were mixed up at some point and it was just happenstance. It was further happenstance that the two sets with the same serial number were close enough in machining so that the engine they were installed in was able to have a normal service life. Of course, to some extent this was a bragging point of GKN and the process. It was happenstance that they were installed on the number 6 journal. The mismatched parts were apparently off enough to fail under racing full power conditions.

I do not have pictures of the interior of the Krebsoege plant but a Rennlist member thoughtfully posted pictures of the Zuffenhausen facility in 1977, including views of workstations. I looked at the minimal work service areas (flat surfaces) and bins full of parts. I thought how very easy it would be to drop/misplace/mix or otherwise confuse two sets of rod components with the same serial number. I also noted that these tours and picture taking had been discontinued -- and one Rennlister speculated that it was because the workers became too distracted from their tasks. You can easily see that in the photos. That is exactly how parts get mixed up -- perhaps the curtailment is testimony enough.

I found it interesting that a number of Rennlisters critical of my theory had read this Zuffenhausen thread and apparently not made the connection. Aside: John, the engine on the stand in one of the photos clearly has a thin sump gasket installed.

Attentional blindness.

Different things are important to different people.

Kind regards,

Kevin

P.S.

You're correct. But it is not me who is confused.

drnick

"happenstance" - kevin, is this the german word for 2/6 failure? in a farsighted joke workers at porsche and krebsoege decided to coin this term after they deliberately used the wrong parts in bearing 2/6 thinking about 928 owners several generations later and saying "this will f!@k them!!"

Kevin Johnson

I was talking to one of my distributors yesterday about an unusual OEM windage tray that had turned up for a big block Chrysler and the conversation turned to mixups at the plants. He said it was fairly common for the different body types to have the wrong suspension components installed on the lines, ball joints for example. There was a lot of pressure to keep things progressing and so long as the vehicle could be moved or driven away from those stations it became someone else's problem. They would have to take the vehicle to a repair line and tear down what had just been built but I guess that was accepted somehow -- this was back in the 1960s and early 1970s by way of the body types we were discussing.

I have heard similar stories from friends and relatives (now retired) working on the lines at other marques -- some stories from within just the past two or three years -- so I don't think it is fair to just beat up on Chrysler or to imagine that workers have changed all that much.

I think the coolest far-sighted act, not really a joke, that I have personally run across came from a worker in the SPAX facility in the UK. Probably 40 years ago one worker took the time to stamp "WORLD PEACE" on the top seam of a Renault damper. I ran across it after it had been shelved as NOS for about 25 years.

Happenstance = Schadefreude? I really don't think so.

drnick

kevin, which 1970s chrysler do you think compares to a porsche 928? im not an expert on american cars but i really did not think that chrysler were making anything that came close to the 928 in terms of build quality, back in the day - dont know about recent times. it translates that they made a different product with different production numbers and probably different processes, im not sure this is a valid comparison.

i think its like saying that the ford GT probably stands a chance of having a wishbone from a focus as they both come out of automobile plants and parts sometimes get swapped over, i mean fords a big company and maybe they took a delivery of landrover parts to the wrong place and they got mixed in with some other bits and were shipped off and stuck on a GT all just to cover someones ***?

i dont think so either.

why bother with engineering an oiling solution for the 928 if all that people need to do is swap there rod caps over? we should simply start a thread where we can reunite lost rods and caps?

are you saying its just coincidence that this failure happened on bearing number six, it has nothing to do with the fundamental problems of 928 oiling? that 2/6 failure is due to incorrect part use - or only this 2/6 failure - but not every other 2/6 failure?

this failure, like every other on 2/6 is secndary to an oiling problem. and your kit was fitted, i believe. so what does that show, you have one race car with one race under its belt and an engine that still starts and one failed engine, both with your scraper - i think the big question is when will the dutch stallions engine go pop!! its probably being rebuilt now in fact...

Kevin Johnson

None in particular -- it is not the vehicle or era that is the problem here but the humans assembling it. Humans are fallable.

I spent time in several different German laboratories in the late 70s and early 80s working with technicians who would have gone through a parallel training process to an automobile technician working at Zuffenhausen (the medieval guild system). My grandfather was a master technician in England and owned a good sized lab in Detroit -- I am pretty familiar with technicians both formally and casually trained. I was both formally trained and informally by my grandfather. It is the human side that is at issue in this particular problem.

The problems still exist.

What you are arguing against is a fait accompli somewhere in the parts manufacturing/assembly process at Porsche or its supplier.

The oiling solution issues in this particular engine failure are separate from the common 2/6 rod bearing failure.


This failure is "just coincidence that the failure happened on bearing number six." I do not think it has anything to do with the fundamental problems of 928 oiling.

The brother rod pair with mismatched parts was more likely installed on another crank pin in another engine of course (7 out of 8 chance for different journal position). If the initial owner carefully broke in the engine and did not race it, it probably had a normal service life.


It's easy to say that -- one can imagine that the bearing insert was misaligned by say, .0005" to .001". The engine used the original pistons with over 100,000 miles on them -- blow by percentage unknown. Blow by works in reverse too; the partial pressure in the chamber can draw in oil past the rings and induce detonation. It would only require a few (one?) of such sharp raps on the bearing insert to cause the ends to converge and act as a wedge blocking and stripping oil and weaking the hydrodynamic force/layer. Et voila, contact between the journal and bearing.

The exposed edge of the bearing insert may have been sufficient in itself to cause failure under full load. Hard to say. Under partial loads over millions of cycles the edge may have been slowly and safely worn away.


This is not an advertisement for my scraper system. The same system that was carefully fitted by Dave in his engine was installed in the Dutch Stallion team's engine (and subsequently, many, many others -- a number of whom have posted on Rennlist) which is why I rule out typical air entrainment failure. Dave did not think that was the problem either, by the way. The Dutch Stallion team's engine survived a whole season of actual racing (43+ hours) and additonal time in practice without showing any wear on the 2/6 bearings -- the first half at 6800 rpm shifts; the second half at 7200 rpm shifts. The engine failed (mid-way, I think) in the next year's season because of a broken serpentine belt. Since it was being raced at 7200 rpms then too, I don't find that belt failure extraordinary. Talk to Rob directly if you care to -- it is not a big dark secret. I am sure the various 911s that were blocking his brother on the track were relieved.

Carl has been testing the scraper system for about three years now. He said he would not add it to his catalog until he was satisfied with its performance and he waited quite a while. Quite a few people have since obtained it through him. I think that's great -- I always try to support our distributors.

BC

So the argument here is whether or not people feel a mistake could be made in a factory or not? Or whether the mistake could cause an issue?

The leanest cylinders under the most load at the time of their being lean, are 2 and 6. Lean conditions cause detonation, and detonation causes an apparent hammering of the rod bearing.

Kevin Q

Kevin, the problem with your theory is it relies on a string of unlikely events.

First there was the dropped cap which just happen to be the same number as a different rod on the engine being assembled. Could happen.

Next the mixed rod and cap have to be near identical to even allow the engine to run without immediately destroying the bearing, never mind last 100,000 miles of, I'm sure "spirited" driving (it is a 928 after all) . Also could happen. Problem is, the odds of all three events happening simultaneously are probably astronomical, especially on a limited production vehicle.

If you want to bolster your theory, measure the mismatch on the inside of the big end using mismatched caps and rods, then see how these numbers compare to the max allowable mismatch to allow long engine life. I think that hundreds if not thousands of mismatched caps and rods would have to be tried before you got one that was close.

I have forgotten all my stats courses, but you could probably work up a rough range of odds. For example, dropped cap, once a week x 20 engines a day x 8 caps = 1/800 caps x the odds it would match numbers in the numbering system (0-999) x the odds of the cap actually being a perfect match. (unknown but likely quite low otherwise the factory wouldn't even bother numbering the caps?) Seems like a stretch at best.

drnick

no brendan, there is no argument - only smoke and mirrors. KJ is obscuring the fact that bearing 2/6 simply failed in an engine that had his scraper, the rest is pure speculation and the product of peoples imagination.

there are no hard facts here and maybe that scares some folk who cant simply admit they dont have the answer. i think mark kibbort may ultimately be correct and that amsoil is the cure for 2/6 failure - his engine has lasted several times over the dutch stallions running time - or maybe this is coincidence? or maybe everytime there is a sample of one no meaningful result or conclusion can be drawn.

i dont care if carl sells lucky rabits feet to ward off 2/6 failure, just cause its on his web site dosent get away from the fact that there was a 2/6 failure on an engine equipped with the scrapers.

i as one of many on this board dont buy KJs speculative red hearing response which completely ignores and bypasses known experience. fact number one, its 2/6 that fails in the 928. asking us to believe a mix up happened at the factory and just happened to affect 2/6 is pushing the odds at many times greater than 4:1 - it would not happen this way by chance and the odds that KJ puts forward in "the theory of happenstance" are aproximately those for the theory that the moon landing was a hoax.

then there are several people telling KJ that most rod bearing end caps like this in the 928, people who would know from dissasembling a lot of 928 engines - this is completely ignored and a story fabricated based on no actual evidence to propose lacsidasical engine building in the porsche factory and supply line. this is a basic affront to anyones intelligence who has seen or measured a porsche engine from this era, it just did not happen this way. even if porsche built the 928 like a chrysler at least what we would have is regular bearing failure of all bearings at an equal rate - but we dont, its almost allways only 2/6.

i know there was another thread about how folks are harsh, but there is only so much BS that one can sit and listen to. i am the person kj refers to a couple of posts up, yes KJ i think your theory is BS - but you argue it like a religious zealot!! you should take your theory to the thread for gearing and amsoil where it can be properly discussed.