I disagree. Rod bearings are not the major wear items. The major wear items in my experience is the valvetrain. Ring failue is far more common. I have a vehicle with over 500,000 miles on it and there is not measureable wear on the rod bearings. So long as lubrication is present, the bearing will never touch the crank. Ever. You make your above statment that the journals should be round and not egg shaped. If you had round journals, you engine would never make it to 5,000 RPM before it seized. It was discovered about 50 years ago that making oval rod bearings made them work perfectly at high RPM. The rod side of the bearing is not the that will wear according to your description, because the force of the power stroke is insignificant compared to the uncushioned slam at the end of the exhaust stroke. The rod bearings will only fail if the engine has been oil starved. The oil hole is always lined up because the bearings position is fixed. I only ever see rod bearing failure if the engine has been run critically low on oil. If there is inadequate oil, the rod bearings are the first to experience oil starvation, and because they are subjected to the most stress, they almost always fail first. In the cumulatative 1.2 million miles on our vehicles the only mechanical engine failure we have seen is bad rings. Our vehicle with the highest mileage has 510,000 miles right now. The engine still runs at full compression, and there is no rod bearing wear that is measurable.

I propose a test. Go purchase a rod bearing, notice it has a slight dull finish. You can wipe it clean with a paper towel. That layer is less than one ten thousandth of an inch thick. In one of our vehicles that has the bad rings, that micro thin film is still there. The ord bearing and the crankshaft have never touched in over 200,000 miles of use. And direct contact will wipe this film off. No tell me, how do rod bearings fail if contact never occurs?

 

I've heard it happen on startup of an engine that's been sitting for too long. The oil drains out of the engine, probably due to a bad valve in the filter, and the engine is completely dry. FOr the first few seconds of running right after startup, there is this terrible thumping noise that slowly dies down to a tick. It sure sounds like metal to metal contact.

 

sorry Khany,

but all engines especially cold, start dry with little or no oil load film for the critical rod bearings...the majority of wear including bearing occurs in the first 5 minutes after start up...leaking anti drain back valves in low cost poorly designed and built oil filters are a major contributions factor to slow oil pressure buildup and added wear...low cold viscosity oils such as many quality synthetics also help cold start oil pressure buildup, 0w?s are the best in colder climates, below 40d F startup temps

another major bearing wear factor is injested dirt especially silica particles with the intake air....air leaks in intake system and poor quality improperly installed air filters are the main culprit

modern passenger car SM rated oils have very low levels of Anti Wear and Extreme Pressure additives such as ZDDP and organic moly compounds not based on modern engine requirements but based sole on EPA cat. converter potential damage from oil additives and new EPA emissions limitations on oil additives...older oils such as SJ of just 4 years ago had twice the bearing and ring protective wear and load additives....both ZDDP and moly barrier coatings are extremely critical for bearing protection during startup until oil hydralic layer protection builds up

rod bearings are easily damaged by oil contamination combustion products acids and combustion byproducts carbon particles in the range of 10 micron and larger.... failure to do regular oil changes per engine manuf are the major cause along with failed plugged PCVs

one of the major reasons for the ultra thin coating you see on bearing surfaces is corrosion protection prior to install

walk into an engine machinists shop up to the specialist running the CNC crank grinding machine with your story of crank main and rod machined egg shaped race or hwy engine journals....they will throw beer in your face and laugh you out of the shop

yes the bearings shells after torquing take on a slight oval shape, 0.0001" > 0.001" but the crank journals are ground and polished to near perfect round, <0.0001" variation and tolerance on quality work and a surface smoothness of less than 10 RA on the best work....the bearing shell crush and bearing shell final out of roundness is primarily to maintain a physical clamping in the rod or main bearing web and for added heat transfer, secondarily wear characteristics except in some special design apps

Clevite's TriArmor (TM) are an outstanding example of modern rod and main bearing engineering
i refer you to
http://www.stockcarracing.com/techarticles/scrp_0509_coated_bearings/

"The best performance was found in a blend of moly (molybdenum disulfide) and graphite. It was so slippery it wouldn't stay on the bearing. Once we found a way to suspend this blend in an inert polymer (PTFE) substrate, we had good adhesion to the bearing without compromising lubricity."

"The benefits of all this are several fold: The reduction of friction results in a power increase. Longer engine life is due to the lesser friction. Also, protection during start-up is no small issue.

"The TriArmor(TM) bearing coating is sacrificial. It gives itself away in the interest of lubricity. Even when the coating is gone, there is still an unmodified Clevite 77(R) performance bearing underneath."

also see
http://www.aa1car.com/library/2005/eb030526.htm

see also Clevite pub.
http://www.engineparts.com/publications/EB-40-06.pdf

 

Yes, that is true that there are lubrication problems at startup. However, this wear only occurs within the first few seconds. The rod bearing is oval because if it is not, when the engine achieves high RPM, the piston slam at the end of the exhaust stroke and the end of the power stroke stretch the bearing, and if it is not oval, it side of the bearing will make contact with the crank.

I don't think you fully understand the operating mechanics of an engine, so I will test you with a little quiz.

1: How many cycles are there in a modern 4 stroke engine?

2: Why are the cylinders honed instead of polished?

3: What is the #1 cause of mechanical engine failure?

4: Do rod or main bearings break in?

5: Does a larger exhaust system produce more average power power?

 

In a perfect world bearings and journals never touch. Perfect means lots of room on the crank for great big bearings, you are not constrained by engine length or crankshaft weight. There are compromises. It also means perfect lubrication. Whenever any of these imperfections happen, momentary metal contact can and does happen. My rods were perfectly quiet but very worn , three layers of metal. Mains were like new.

This is no big deal. All I said was to check rod bearings when you are looking at them. It is free and easy. By the way, rod bearings do spin just like mains. They only rock in radial engines, other than the master rod. Think of the crank journal as an eccentric and in your mind bring the centers of journals together to match the main journals. Rod bearings rotate. (period)

Ken

 

Oh I love tests.. LOL

1. 4 right! in, comp,pwr, exh

2.ever seen a chrome bore? ring seating.

3.the operator..no oil.

4.nope

5. no just on WOT

Hope I didn't give the answers away..Do I get my ASAE cert now? LOL


Dick

 

Khan:

I think you mistook "eccentricity" for "ovality."

Under load, the center of the bearing and the center of the journal are slightly separated, due to the fluid flow in the gap.

This has been well known long before 50 years ago. It started with a set of experiments by Beauchamp Tower (an Englishman) in the 1880's. The theory was first developed for the slider bearing by Osborne Reynolds (an Englishman known as the father of modern day Fluid Mechanics), and this class of fluid flow is known as Hele-Shaw flows.

In short, the load on the journal is roughly propertional to the rotational speed and inversely proportional to the square of the gap. So, the higher the load, the smaller the gap, and the more eccentric the journal and the bearing become. You don't really want an oval shaped journal since that would set up instability waves which would destroy both the journal and the bearing should you run into resonance.

As far as lubricants go, not everything is suitable. You need something with low viscosity and high flashpoint, since there is a region of very low pressure in the flow. Fluids with low flashpoint will cavitate and ruin everything in a hurry.

 

Gentlemen,

Knowledge is power. This forum is he best I have seen. Friendly disagreements lead to greater understanding. I love this place.

Ken

 

I'm telling you rod bearings do not spin. Allow me to illustrate. In fact neither do the mains, the bearings remain stationary and the crank rotates. The main berings never move, and the rod bearings only turn 15 degrees.
They rotate 15 degrees in one direction and then 15 degrees in to opposite direction against the direction of the crank. The crank spins, but as a whole, the rod bearing is stationary. It no more spins than the rod itself.

From my standpoint, you believe the way you do on this subject because you have been taught by "experts". These "experts" were also probably taught by "experts" and when you get back to the source of these teachings you have some backyard mechanic who acheived his "expert" status by being the editor in some magazine, or maybe he was a mechanic, or whatever the case may be. Fact is, these virtues do not make them experts on something, and boy can we humans be gullible when we assume that an "expert" knows what he's talking about. What mental laziness. We are intelligent people, lets not take mental shortcuts by assuming that the "expert" has alreadt thought it through.

One expert could tell you that letting your tank run low would ruin your fuel pump and plug your filter. This may be true, but simply stating that leads to no increase in knowledge, does no educate you concerning why this happens, etc. It also does nothing to really educate you about the circumstances that can couse this to happen. Most of us are probably aware than a tank that is full of gas does not collect condensation. And condensation causes corrosion. It is also heavier than gas so it runs to the bottom of the tank. And when you let the tank run empty or extremely low, this gets drawn into the pump and can do its damage. However this condesation only occurs if the vehicle sits for any length of time. Vehicles that are frequently run low and are used very often do not fail or plug the same way, so long as they are not allowed to st with a low or empty tank. Also plastic tanks do not corrode. The recommendation is to never allow your tank to run low. I say if you never allow your tank to run low, then the moment someone does run it low, the filter will instantly plug and the vehicle will in all probability become undrivable. Seen it happen myself. My grandparents never let the tank go below half full. They did not drive the vehicle often. They were following the advise of a mechanic in the newspaper. One day Grandpa forgot to fill it up and ran it out of gas. He someone stops ad gave him some gas, but it wouldn't restart. They had it towed. It needed a new fuel pump and a new fuel filter. Our own vehicle are run till about 1/8th tank and then refilled. They are used more frequently. The fuel filters are replaced at the recommended intervals. When ous get run empty, which is rare, they start right up when they are refilled. So you can se from this, that this advice is not black and white. If the material is flushed from the bottom of the tank more often it will not plug the pump or the filter spontaneously. But if if is never allowed to run low, you had sure better not ever let if run empty, or you might be looking at some expensive repairs.

Back to the main topic, I will quickly outline some facts.

1: 95% of all engine wear occurs withing 10 seconds of startup.

2: Most of this wear does occur at the rod bearings but much of it also occurs at all other moving parts. The pistons are the last to recieve lubrication from the oil.

3: Unless the engine is run low on oil, the bearings experience no physical wear.

4: The remaining 5% of engine wear stated above can be broken down as follows 4% Chemical wear (this occurs when the engine isn't even running, this can be prevented by using premium quality full synthetic oils, changing oil frequently, and by taking the vehicle on long drives at cruising speeds often) The remaining wear is the valvetrain, and this wear occurs while the engine is running.

5: Engines that are run on frequent long trips last longer. They do not need their oil changed as often. The major cause of engine wear is minimized.

6: It is possible to reduce the major wear factor to as low as 20% or less of total engine wear. This can be obtained by finding ways to lubricate the engine before it cranks at startup. This can be achieved using electric oil pumps, or pressurized oil accumulators. I will provide some links at the bottom of this post. I do not use any of these products at this time, though I will probably do one of these on my Aerostar, since it has the lowest mileage. I also only use premium oil filters that meet OEM specs. This ensures that they filter properly, do not disintegrate, and have the correct check valves if applicable.

7: Even oil that has begun to disintegrate will lubricate well, however, it becomes increasinly corrosive, and chemical wear increases.




For some good reading, I suggest these sites
http://mototuneusa.com/thanx.htm
http://www.thinkauto.com/accumulators.htm
http://www.amazon.com/gp/product/B00...reative=380341
http://www.northerntool.com/webapp/w...70_47671_47671

Additional fittings and parts may be required. Works best when used with a oil filter relocation kit.

 

Dear Khanty,

Your contributions are great and have taught me much and I thank you for them. But, darn it, rod bearings spin just like mains and in the same directions but with more problems like centrifugal loading and poorer oiling.

Think about it. What if the stroke were .5 inch. Would the rod bearings spin then?

I love your opinions but you are all wet on this.

All I say is check the darn rod bearings. They are smaller and receive second-class oilng. They are super easy to check. They are stocked at the auto parts stores, mains are not. Mine were shot when mains were like new. (your thoughts on perfect lubrication.) Since I think about kinematics, I get it wrong too. Think about it.

Ken

 

Ken & Khan:

It makes no difference what spins and what's stationary. It's the relative motion between the journal and the bearing that counts. You are both right.

From the journal's point of view, it's the bearing that spins. However, to the bearing, it's the journal that spins.

Same difference between Galileo and the Catholic Church.

As for checking the rod bearings, why not? It takes only a few minutes and a good torque wrench.

I would even check the main bearing sice that's pretty easy too once you are down there, but not the main cap on the rear of the engine. Leave that one alone.

I can also understand Khan's reluctance to open up the bearings, since you don't want to get dirt in there. Any dirt on the bearing surface will score both the journal and the bearing, and that's bad news. Be very very careful and very very clean when you open up the caps.

Can we get back to opening up the oil pan now?

My experience with the oil pan is that you don't need to jack up the engine. The main sticky point is the rear of the pan hitting the transmission cover. For that you have two choices:

1) If you already had the tranny separated from the engine as suggested by the manual, cut the transmission cover in half. The top half goes between the engine and the transmission. The lower half is held by the bolts on the starter on one side and some screws on the other side. That's plenty to hold it in place. Next time all you have to do is remove the starter (you must do that anyway) and two screws on the other side and the lower half of the cover falls off. Then you would have plenty of clearance to get the oil pan off and to clean the back side of the engine.

2) If you didn't remove the transmission, unscrew all the transmission-to-engine bolts by exactly three turns. Then remove the two bolts on the transmission mount, jack up the transmission slightly, and slide it back until it stops. That moves the transmission back about 1/4" (but still keeps it on the guide pins) and it would give you enough clearance to get the oil pan off with ease. No need to disconnect any wires or driveshafts or any Flexplate nuts.

 

i like to disconnect and slide the transmission back and takes little more time with a screw adjustment tranny jack.....

on manual tranny allows inspection of full inspection of clutch, pilot bearing and throwout bearing, firm believer in new throwout bearing every 50k miles, they're cheap compared to option 2-the blown bearing disintegrated clutch 200 miles away from home mess

pulling back autos away from the block allows inspection of the flex plate, crank spacer and replacing the front seal if >100k miles...a large percentage of the factory powdered metal crankshaft spacers have fatigue cracks allowing converter misalignment and failure and incorrect support of the TC pilot
major case of TC failure.... too many new/rebuilt TC's have been mated to a cracked failed crank spacer with resultant failure of the new TC in 1k miles or less

 

You are correct that rod bearings will fail more that main bearings. Let me explain why. The rod bearings receive lubrication before any other moving part of the vehicle. They crank is always spinning the same direction within them. The rod bearing receives lubrication second. However, they are subjected to more stress. If you read the last article in the link regarding break in secrets, you will find complete illustrations. If you read the part regarding rod bearings, you see that in the first part of the rod bearing (which is fixed within the rod by the way) rotates 15 degrees in the opposite direction as the crank. Now if the rod bearing and the crank are moving in opposite directions some of the time, and the main bearing is moving the same direction all the time, which is going to wear faster. Obviously the rod bearing, which will also fail the first because it gets the oil last.

No to be unfriendly, because frankly, your expertise and experience are really appreciated, but what I am saying is science. It is observable, repeatable, measurable. What more do you want. Tell you what, prove it to yourself. This is very easy. Find something with a crank handle. A hand drill, a hand powered pencil sharpener. Anything will do. Now if it has a sleeve around that is better. this represents the bearing. Now if you grip it with your hand this is emulating the bearing, because in an engine it is locked within the rod once it is assembled. Within that rod, it cannot move, because it is locked in there with an interference fit. Now if you turn it by hand and observe from the end, and you can place a mark on the "bearing" and roate, do it move? Yes its absolute position changes, and its angle does change, but could it be called spinning? Its position relative to the rod is fixed, and by looking from the end, its angle changes by about 15 degrees or 1/24th of a turn in either direction, depending on the phase in the stroke. But its while it is true that its angle variation depends on the length of the stroke, but in the most extreme posible variation the bearings angle relative to an observer at the front of the engine would rotate by 30 degrees, if the stroke got any shorter, greater angles would be possible, by the rod would also break because the side forces on it would exceed the linear forces. The piston would also be damaged by extreme side forces. You can't measure the the bearing as rotation relative to the crank, becuase tht would be like measuring the rotation of space relative to the earth being stationary. Thats just not they way it works. There are considerable speed differences between the bearing and the crank. The same with the main bearings, except they are stationary relative to the block. They do not even undergo an angle change (unless you want to count movement of the vehicle) However the crank is moving canstantly within this bearing. Now when I say bearing, I mean the literal definition known to mechanics the world over. The bearing is the metal sleeve that comes in 2 parts that fits inside the rod housing and goes around the crank. It is intended to prevent another more expensive less replacable part from wear. I this case the rod itself or the block iteself because if they wore down, they can not be built back up from a practical standpoint. Please Ken I beg of you on this subject, do this test. If you are a mechanic in a shop, there should be something with a crank handle like I have described, like a lathe for turning brakes, or something that has those style handles. The larger the better.

Ken, I do highly respect you and have found your posts to be informative in general. And I will agree with you on several issues to prove this. You made the statement that rod bearings are the most common failure. Since I can niether prove nor disprove this, I will agree with you on this premise. If you run the engine out of or extremely low on oil, which probably happens more often that you and I realize, the rod bearing with be the first thing to go because they are the last bearings in the engie to receive lubrication. The piston rings can withstand some direct metal to metal contact but generally don't because they are lubricated differently and have variable tolerances. In experience, I have never observed rod bearing failure in a properly maintained engine. I have seen where rings have collapsed however.

Now, before you respond to this post, I want you to do two things. I want you to read this entire article and think about what the author is saying, not just blindly accept or reject his statements. Then I want you to observe plain bearings in action (ball bearings work differently and do not make good illustrations). The author has included many illustrations so you can observe what he is telling you. This is the link and please read the entire article before you respond. http://mototuneusa.com/circular_logic.htm

 

khantyranitar!

As I can see, engine wear is not the most expencive problem. The average engine life from rebuild to rebuils is about 5-10 years ore 300-400K, even with frequent short distance trips. I use to start and stall my aero 10-20 times a day. So I had to replace many starters. My engine was rebuilt ones, when it was 250K on clock and now I have over 620K and I have slight nocking sound when engine is cold. 3.0 V6 when it is old leaks oil, leaks more then burns. My leaks from the mane seal, from the oil pan seal and from the head covers. I add a quart of oil every 1000 miles, but there is no blue ore black clouds from the exhaust pipe. Well, I gonna drop the oilpan this spring, replace bearings and may be I will find a source of nocking sound (it seems to me, that the rod bearing nocks), I will replace all the gaskets, main seal and clean all... And I'm sure, I will do niothing next 50-100 K.

Well, what is the most expencive in aero's maintenance?

My raiting
1. Fuel
2. Suspention (shoks, BJs, Insolators)
3. Steering (rod ends, rack'n'pinion seals)
4. Tires
5. Brakes (pads, shoes, cylinders and..... etc.)
6. Engine overhaul, spark plugs, wires, sensors, connectors
7. Batteries (every 2 years)
8. Clutch (disks, pressure plates, bearings, hydravlics)
9. Body
10. U-joints
11. Bulbs, Locks and other....

So engine rebuild is rare procedure, but maintane engine well, becouse to rebuild it in workshop is expencive, to rebuild it in garage is difficult... well, for me it was more difficult to pull the engine out of van and install then to rebuild.

 

Is there a typo here? These two statements seem contradicting.

It's true that the rod large end (and thus bearing) rotates as the rod moves up/down and side/side, but it rotates against the rod journal on the upper halves of each stroke slightly uncreasing the relative velocity between the bearing and journal, and with the rod journal on the lower halves slightly decreasing the relative velocity. It is a net loss, as frictional force and wear increases with the square of the relative velocity.

When you use words like "spinning bearings", I think of a bearing that for whatever reason been run with no oil, and had developed so much friction with the journal that it locked, and got spun around in its seats. Those tiny tabs can't really hold much force in those situations.

I like the idea of pre-oilers, but I doubt many of them will be able to generate enough pressure to completely keep the metal parts separated. What they will do is to push oil in all the passages so that as soon as the oil pump starts turning, it will generate pressure. But by that time, the engine has already moved some parts with metal to metal contact. It's the unfortunate nature of babbet type bearings.

Back to oil pans: I still prefer to separate the transmission when dropping the oil pan; it lets me jock the engine around. This may not be necessary for a 2wd, but the larger crossmember of the 4wd gets in the way of many of those pan bolts, and short of dropping the crossmember, jocking the engine around is the only way to get at them.

The other thing you can do when you separate the transmission is to completely drain the torque converter for a complete flush.