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Terry Haines

Conrod Bearing Info

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Guest KAOS_2.5M
...we will focus on the lube system. What gets oil pressure first etc...the crank!!

 

indeed, with no oil pressure the steel crank will be riding on the soft aluminum liners, not a cushion of oil like it's supposed to be.

 

epic fail!

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....the FIRST area fed by oil from the main oil gallery is the MAIN BEARINGS of the crank...the feed for the ROD BEARINGS is from a drilling within the crank to the rod journals after the mains are supplied ...so if oil pressure has failed the first bearings to see air Vs oil is ....the main bearings.This is the primary area of lube on all engines, mains first.Other drillings give a restricted pressure feed up to cam shafts etc, chain tensioners...and secondary lube(splash) to other parts such as valve guides etc....

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...so when oil supply to the crank is lost,by whatever reason,the first thing that happens is the bearing surfaces of the liners,is usually wiped off due to no lube and increased friction and metal to metal contact. This will NOT affect the nip or crush of the bearing liners and should not cause the bearings to spin...Take a look at the many sites of bearing makers...most all will show pictures of common bearing failures...With 'lack of lube' it is not common for bearings to spin.This has also been my experience in 100's of engine teardown inspections in the past...next step..'So why DO they spin???(also note that most V6's do not have damaged main bearings....the first bearing that will see air if lube supply is cut off!!)

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So since metal to metal contact does not cause the bearings to spin when nip/crush is correct, than what causes it? Increased OD of the big end and/or improper fitting of new bearings?

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...when nip/crush is correct

 

....and when nip & crush is INCORRECT and out of spec so it can spin!!....ready for the next phase? We will 'assume' the issue comes from lack of nip & crush...Will give my 10 cents on the lube later... Next would be 'how does the nip & crush go out of spec....??????

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General Info on PM/Sintered components,incl conrods.

 

First off we all need to understand how these components are made.Once you understand that you can see how they 'work'.

For a close example get some styrofoam packing...say a moulded part. The outer 'skin' is quite tough and resists breaking and holds a fair amount of pressure and load, as does a PM part,the 'skin' is the toughest part of any PM component.Now scratch off that skin to expose the styrofoam balls ets in side...Not as tough is it...and as you go deeper in the amount of compression of the balls becomes less and is softer with less bonding the deeaper you get.With that in mind think of the balls as the PM powder.

The powder or 'blend' consists of steel usually...Can be high carbon, stainless etc...The powder alone will not hold together,even with heat, without a 'solder'...a metal that melts at a lwer temperature that the 'main' material. In most cases this is a brass,bronze or copper solder mixed with the steel.The 'blend' or mix decides the ratio of these mtals, powder size etc.Stage one after the powders are blended ,is to fill a mould and be sure there are no voids withing the loose powder,next is the initial pressing, to form the powder to the shape of the mould.This is usually a high tonnage press ...but we still have not added heat...The powder will hold in one piece...but if you drop it it will fall apart.

Once moulded the component is put thru a sinter furnace...raises the temp to the melt point of the solder....once ht enough the component is again placed in a higher tonnage press to force the semi fluid soilder and main metal together. This is also the stage that gives the smooth outer 'skin' to all PM parts....

Points to note here are that the final pressing or forging , is done on conventional presses/forge...from side to side in the case of a conrod...Think back to the moulded foam...Even a press the tonnage compressing the powder or 'balls' reduces the closer you get to the 'core' of the component so the 'bind' between each particle of powder gets less.Many factors affect this process...blend of powder,temp and press pressures etc etc....Are we with it so far??

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...so now we have a formed component/conrod with a very tough outer skin.Very strong....so now we must machine away some of that skin to finish the componet/ rod...great idea eh!!

 

We need...

 

The width of the rod correct at the rod end and wrist pin sides, we need two bores machined, one for the wrist pin bush the other for the rod bearing liners, we need two holes,threaded for the rod cap bolts and machine the rod cap balance pad..So lets rip off that nice tough skin....and it makes no odds how sharp the tools are we still remove the toughest part and reveal, be it cut, the powder towards the core...Get a sharp knife or hot wire and do it to the styrofoam...No matter how good a cut, the skin structure has still been compromised...Then we can cool/crack the rod cap (look inside a conrod cap join line)...see how 'open' and grainy the structure is?...THAT is the powder.....Looks a bit like cast iron....

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I've noticed the powdery look at the cracked end. Not really porous, but grainy.

 

Since Ford is all about penny pinching, how did this method come to be? Is it less expensive than producing cast rods? PM rods are lighter and stronger, yes? I guess mixing in the solder requires less steel, therefore less cost in materials. Cast rods seem to be more durable though. I know other manufacturers followed Ford and use the PM process.

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Guest KAOS_2.5M

copper is more expensive than steel, and I'm fairly sure bronze and brass are as well.

 

I would suspect the cost savings is from the reduction in energy used to heat the metal. have to get steel pretty hot to make it molten for a cast rod. the PM process doesn't so much melt the steel completely as braze it together with "solder"

 

now think on this, which is stronger, a welded joint or a brazed one?

 

I suspect all of this is just to cut down on the power bill

 

[edit]

 

also wanted to add that the retooling for the PM process also saved them a ton of money in machining the diff gears, so why not use it for everything.

Edited by KAOS_2.5M

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...FYI..PM rods have been around foe years and started on outboards.Other rods are either forged or billet m/c...not cast. PM rods, when designed and made correctly work well...within limits. Cost is part of it but less weight variation and reduction in weight is also a factor.

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...a few thoughts and facts on the lubrication theory of rod bearing failure.

 

*The bearings on most all 95-96 V6's have hardly ever failed*The problem seemed to start with the SVT engines*The design of the lube system and components has been unchanged from 95>2000 *Ford were not able to replicate the failure on testing of an SVT on track etc with many turns etc*Most all SVT engines that have this failure happen at around 60> 80,000 miles*Despite what owners think, the design of the conrod was changed around '97, look at an early 95 rod against a 98 rod...It is not the same, part numbers did not change but something did.(supplier,design,process etc)*Non SVT 2.5's(98>) have failed but usually at 100,000 or more miles*Some owners never have an oil light on when the knocking starts* Some owners are still able to drive with the knock and still no oil light on!...

 

Makes you think eh!!! :blink:

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yeah, the '97's engine was knocking when I bought it. No oil light, the engine continued to run. Starts right up every time and idles fine. A bit down on power, but it also has over 130k miles from previous owners who poorly maintained the car. I tried a few times to rev the engine to death before pulling it. The knock got a little louder, but it wouldn't let go.

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...yeah, the '97's engine was knocking when I bought it. No oil light, the engine continued to run....

 

....well no S**T!...So you had oil pressure eh and a knock....Have to say I'm NOT suprised....The lube issue is a myth....which we will dispel during this subject/post!!!.... :D

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...so lets put the 'potential' lube issues to one side for now,I will return and discount those later.

For now lets just 'say' that the bearing liners loose nip & crush which causes them to spin. This is no reflection on the INITIAL strength of the PM rods....

With so many failed engines on my hands over the years,I chose to tear them down and inspect/measure.Most all were SVT units and had at least one spun rod bearing and a damaged rod(parent bore) from the bearing spinning.

First off I had some 'new' genuine Ford rods around. From the failed engines I would take one or two rods that had not failed.Was sure to clean the parent bore housings with acetone and measure the parent bores of those rods and compare to the Ford specs and the specs of the new rod(I also backed up 'my' measurements with data from measurements taken on the parts at a local tool & die shop with a CMM,I was within a couple of microns) . In ALL cases I found the used rods were either out of spec at the top end(parent bore too big) or very close to being out of spec.The new rod came in at 'median' or middle of the Ford spec or a little above the median.

Think back to the styrofoam rod, the usual miles that the engines fail and the MAIN point, the difference in loads that the SVT Vs non SVT rods are subjected to...

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Guest KAOS_2.5M
...I think you are jumping the gun here. I think the how comes before the fix etc!!!...Want to explain what goes wrong??

 

 

the heat and preasure from the liner exerting a force on the parent bore compacts the air from the PM the parent bore is made from, making it larger, right?

 

I just had another idea, why couldn't a machined steel barent bore be welded into an even larger parent bore in the PM, then machined to take the liner.

Edited by KAOS_2.5M

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Guest KAOS_2.5M
...no and wait a little longer before you jump here! :rolleyes:

 

 

sorry, so why does the parent bore stretch?

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..so lets think back to the styrofoam rod 'model' and the amount of pressure on the 'core' powder when the rod is made.

Over time that 'core' is subjected to large loads/forces...The core powder is not as strong as the 'skin' and over time the loads cause the rod parent bore to distort/become larger and the bearing liner looses it's nip/crush.A new rod will not fail 'but' over 1,000's of cycles it will AGE and loose dimension. The rods have an issue with STRESS LIFE and EXTENDED DURABILITY. Measurements have shown me that this is the case and once the nip/crush is lost, the bearing liner will spin and, as mentioned, the engine can still have oil pressure AND a knock from the failed bearing...

The SVT engines make higher HP and the rods(same as a non SVT) are subjected to higher pressures and loads...one of the reasons SVT 2.5's fail before post 97 non SVT engines...

I should also add that during my measurements etc ,I contacted suppliers that I know in the 'PM Triangle' of Pa, an area with many PM parts suppliers and engineers that deal with PM every day. The overall advice and comments matched my own.Many made reference to possible incorrect initial dimension specs, bad or incorrect powder blends,incorrect press/forge pressures and incorrect sinter temps...some or all of which could cause errors in compaction of the powders,giving long term duarability issues.

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Guest KAOS_2.5M
..so lets think back to the styrofoam rod 'model' and the amount of pressure on the 'core' powder when the rod is made.

Over time that 'core' is subjected to large loads/forces...The core powder is not as strong as the 'skin' and over time the loads cause the rod parent bore to distort/become larger and the bearing liner looses it's nip/crush.A new rod will not fail 'but' over 1,000's of cycles it will AGE and loose dimension. The rods have an issue with STRESS LIFE and EXTENDED DURABILITY. Measurements have shown me that this is the case and once the nip/crush is lost, the bearing liner will spin and, as mentioned, the engine can still have oil pressure AND a knock from the failed bearing...

The SVT engines make higher HP and the rods(same as a non SVT) are subjected to higher pressures and loads...one of the reasons SVT 2.5's fail before post 97 non SVT engines...

I should also add that during my measurements etc ,I contacted suppliers that I know in the 'PM Triangle' of Pa, an area with many PM parts suppliers and engineers that deal with PM every day. The overall advice and comments matched my own.Many made reference to possible incorrect initial dimension specs, bad or incorrect powder blends,incorrect press/forge pressures and incorrect sinter temps...some or all of which could cause errors in compaction of the powders,giving long term duarability issues.

 

 

thats basically what I thought, with the exception being that I just thought it was because all powder metal rods would fail.

 

so it's possible to get a "good set" of rods which don't have these manufacturing faults?

 

I wonder if all the rods are manufactured by the same supplier, or if theres a "bad" rod supplier. also wonder if there is a way to tell which rods are no good before they fail and tear up other parts.

 

is there an issue with the 3.0 rods too? seems like if 200HP will ruin the PM rods, 235 would really ruin them fast

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..best I can say is 'younger rods' should last longer.Have no idea on the limit of distortion or if it stops at future point. I doubt Ford feel there is any issue with these rods but I would have to disagree with that or in fact any of my peers or fellow engineers who still feel hooked on the lube issue.We have also seen spun bearings on some 3.0..The rods are now the same part number for both 2.5 and 3.0. There is no 'fix' for this but some pro engine builders do have 'tricks' to increase the nip & crush but as stated if the parent bore moves away from the liners,over time, all you are doing is playing 'catch up' to a point where,due to the rod distortion,the bearing looses nip & crush and again...spins. After market forged rods would be a true fix to this issue but most DIY owners who swap bearings etc do not have the skills to even 'feel' if a liner fit is suspect let alone carry out the involved measurements I have listed....and even if they do,it may be ok 'now' but what about as the rod ages and fatigues.

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...with so many views but only input from a couple of members,maybe it's time to edit some of the posts out etc and pin the subject...any objections,comments etc...Would like to get the info to flow a bit better before we address the oil/lube myths etc..

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I think most are content to "sit down, shut up" when it comes to your "teachings" Terry.

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..thanks. I'm just trying to sweep away some of the dross that owners, for years, have been given about rod bearings, lube system etc...I'll give my thoughts etc at the end. Basic problem is most do not fully understand the engineering within the lube system or the basics of bearing design,conrod design etc and go off 'gung ho' throwing bearing shells all over the place! Peer pressure can take away any personal judgment or objective thought...I tend NOT to go with the flow...I want a 'root cause' ,just my nature!!

I mean, one of the first thoughts was Clevite bearings are harder!..That for starters is BS as anyone with some degree of engine build/ automotive engineering background would know...Ignorance is NOT bliss...open up the gray matter and THINK!!! :blink:

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Guest KAOS_2.5M
I think most are content to "sit down, shut up" when it comes to your "teachings" Terry.

 

+1 there

 

I love to learn, and especially love to learn "WHY", not just that it 'IS'

 

nobody can really know anything unless they get the logic behind the WHY

 

I'm am also surprised nobody else wants to ask any questions in here. so much to learn

 

edit away terry, it's your class

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