Can we solve the rod knock?

I don't know if this is the right place to post this so please move me if I am wrong.

So today I will be putting my old 2.5L up on the engine stand. It had a rod knock from like 3500 RPM to 5000 RPM or so and then it suddenly got worse and knocked at all RPM's really loud. So I stopped driving it before it threw a rod.

I am very curious as to why these engines are so notorious for rod bearing failure. People say bad rods, but I don't think the rod casting process these duratecs use is any weaker than anything else. People say oil drain back, but then wouldn't the main bearings be the first to go? Could it be poor quality bearings? Could it be too much harmonics on a poorly balanced crank? Does evrybody who drives these cars beat the crap out of them? I want to figure this out or at least try to make a little progress.

I will be taking the bottom end apart and checking each rod for bearing damage, I will be measuring the rod bearings ID from top to bottom and side to side. (I think if the rods stretched they would be longer top to bottom and narrower side to side)

I imagine this has all been done before but I notice most rod knocks throw the rod so we cant measure it. If there is anything else you guys think I should measure let me know I will be posting pictures.

A little more info. This is a non SVT 2.5L the original owner put on a DMD (I am not sure what mileage) I can't remember when the rod knock started but I stopped driving it at about 75000 miles when I knew the rod was about to go. I was agressive on this car within reason it was raced a few times and spent alot of time at WOT (which most engines should be able to withstand) It got synthetic (Royal Purple Napa gold filters) oil changes every 5000 miles since I bought it at 60000 miles. (I don't know what the original owner did but he took great care of it so I imagine it was close to the same) If there is anything else you guys would like to know about the engine let me know

I am curious to learn so help me out. Thanks guys
-Brian

I got the pan and tray off... and all I can say is wow. I found my culprit immediatly it was the number 1 rod. I went to take off the cap bolt and when I put torque on it it shifted. So I just grabbed it with my hand and I could move it back and forth and up and down. I was amazed with the amount of slop. So I pulled it off and I'll just let the pictures speak for themselves. and I took cylinder 2 out for comparison.





CYL 2




CYL 1






Any thoughts? The tabs on the bearings that hold them in place are totally gone. the edges that mate are completely rounded and they slip right under one another. what could cause this?

That's what we call a "Spun rod bearing". Been there done that but not in a Contour. On the car it happened to me is was due the previous owners abuse of the engine, unknown to me until the rod started to knock. In your case it could be a little abuse, high rpms, normal wear, etc. What happens is the crank comes in contact with the bearing when the oil film fails and the bearing tries to rotate with the crank journal. IF it happens enough the two seize and you have parts breaking.

In your case as well as mine we stopped running the engine before it got to that point. You might be able to put it back together after just having the crank ground and new bearings. I would not reuse that rod. The others should be OK. You should be able to get one good rod either here or at a Pick-n-Pull.

I already built a 3L and almost have it running. I am not trying to re-use any of these parts. The reason I am doing this is because the Duratec seems to spin rod bearings more often than any other engine I know of and I want to know what causes this. Like I said in the first post some say it's lack of oil others say the process they use to make the rods isn't strong. So I just want to know why these engines are so notorious for spun rod bearings. Where is this engines achillies tendon coming from

and before anybody comments on it (because I know you guys will) I already flipped cylinder 2s cap around I know it is backwards in the pics

I've seen plenty of well designed rods with all the drag racing I used to do. I don't really care for the bottom cap on those, wouldn't be surprised at all if the weak areas between bottom balance pad and the bolt bosses allow the bore to go egg shaped at high rpm chiselling oil off the split area to seize and spin. Meaning the flaw is designed in, only different rods will cure it.

Ok is there anybody out there who has spun a rod bearing with aftermarket rods? please chime in

and I mean for unknown reason not loss of oil pressure or anything like that

I don't believe that they has been anyone. plus only a small group have run aftermarket rods.

I'll share my experience.....

My original stock 2.5L spun a bearing for no apparent reason at 93k miles. The oil level was fine and I never pushed it hard through corners. It just gave out one day and made it about 10 miles before it was no longer driveable.

My 3L was built with Clevite 77 rod bearings and main bearings. For some reason, my 3L has consumed oil from day one after the install. I don't know where it's going because it doesn't leak anywhere. Bone dry all around the block. Because of the oil consumption, I tend to run very low on oil before changing it out. I do top it off sometimes between changes, but I usually forget near the end. Because of this, I've had my oil light flicker on for a second multiple times in the last 4 years. It's usually cornering into a parking lot or turning onto a street. I panic and go grab some oil immediately to bring the level back up. Everytime it happens, the motor continues to run just fine.

I have a 3L hybrid so the oil drain back problems on the 2.5L still exist on my setup. At this point, I don't think the drain back problem alone is the causing of bearing failures on our motors. Now combine that issue with weak bearings, and it makes more sense.

According to the forum posts, my engine should have been dead years ago. "Oil light flickered, is my engine shot?" "Yup! Start shopping for a motor."

and to add to that, I have taken right hand on/off ramps at speed and high rpm, oil pressure reading at the head or the main oil galley has never changed during these times. But then again I always run 6 qts of oil.

So when people say it's because of this or that everybody is right? the rods are weak and go egg shaped, the bearings are weak and with the slightest loss of oil they "spin", and we do have oil drain back issues so once you lose your pressure for a second then there is the loss of oil from my last point. Now, what is the deal with 3L? I have read people spinning bearings on new 3Ls and they use the same bottom end so same bearings? but the oil drain back was fixed so the weak bearings don't fail as much because they always have pressure. Is that the only thing that makes the 3L stronger than the 2.5? Are clevite's the best upgrade?

if there really was a oil drain back issue I would beleive that the crank bearings would go first ... since they are the first place oil goes after being pumped through the oil filter.

It may not be loss of oil at the rod bearing that cause them to spin, its the rods stretching and then the bearing isn't retained in place as it should be.

from my understanding the clevite bearings are softer then the OEM bearings. Also there was some theroizing that 3l would spin bearing because of using the taurus oil pan in the contour.

I also believe that alot of people run low on oil and never realize how low it is until its to late.


check the archives, there have been many discussions and arguments about this. Also check out FCO and what Terry has to say about it too.

If the 3L spins because they are running low on oil without knowing it because of the taurus pans, the mains will still be the first to go right? I have read most of the arguments, I was hoping because I have my engine apart there was some way I could figure out what is causing it. I will be measuring the rods today to see if they stretched

Uh, no. NO. Most engines fail rods first because they are loaded harder on smaller areas and rod cross sections thinner, bearing not supported like in mains. Block webbibng pretty much keeps the bores round. Centrifugal force plays a part there too, harder to get oil further out on the beam. Mains not off/on tension/compression loaded nearly as bad as rods. Rods getting oil last too contributes. High rpm oblongs the bore, mains do not really do that.

I've seen hundreds of spun rods, but only a few mains, the mains usually were the result of something wrong at time motor put together. Look at normal wear, most engines will wear the rods out before mains with normal or low workload during motor's life. Seen it in a hundred torn down engines.

If motor not loaded, I've seen them last for years with flickering oil light occasionally, have done it myself. Had one AMC car that held maybe 5 psi at idle for years. As long as pressure swings up at rpm increase all right. That car leaked badly and I always kept a quart handy to fix the flicker. Now if that same flicker occurs high rpm and loaded hard, kiss that engine goodbye. It'll tear something up in maybe 2-3 seconds with no oil.

Again, that bottom cap design sucks. There should be some ribbing on it to stiffen it up. It doesn't look like a forging either, it appears to be cast or maybe sintered. Both are weaker parts. Stronger rods always begin with the word forged.

amc49 said:

Again, that bottom cap design sucks. There should be some ribbing on it to stiffen it up. It doesn't look like a forging either, it appears to be cast or maybe sintered. Both are weaker parts. Stronger rods always begin with the word forged.

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I have to agree completely with you. Especially on the poor design of the cap end of the rod. I have seen some rods on other engines that had no rib but they has a thicker cross section. Also those rods are sintered. I think most OEM rods are now sintered unless it's going into a high rpm/high powered engine. I have read some on sintered rods and the process and resulting rod is a good product but only if the design is correct. The one thing I did read is the most rods of this type manufacture do not like high rpms. The quick reversal of load starts to tear them apart at the morlecular level resulting in the stretching that occures in the Duratec V6.

Well that is alot of good info thank you guys. The sintered process (for some who may be reading and might not know) is casting the entire rod as one and then breaking it at the cap so the two peices match up perfectly. This is claimed to be stronger seeing as they have a tighter clamp around the crank. As for stretching, if this process was weakning and stretching would it not be the same for any other engine that uses the same process? Or are cars with duratecs more fun to drive than anything else? (haha I'm gonna go with the later) and by that I mean we take it up to high RPMs when our engine is not really built for it. As I would like to still leave this thread open for discussion because it has good info, I am finding most info shows that there is not a "solution" for this problem that our duratecs suffer from other than changing the weak rods. I believe that will stand based on the info that people have been collecting for years. Until a forged engine spins a bearing for unknown reasons...