Two of these are not like the others - #5 Rod Bearings Spun

[Ramage]

cylinder 5 bearings did not come off with the caps they were somewhat stuck on the crank. Car had some start up rattle for a few weeks. On Thursday May 29th I noticed what I thought was rod knock. Since I had already purchased all the parts to do my Rod Bearings I started the Job this morning. The good news is somehow the crank is fine.

Car has 135000km / 83000 miles.

[BL92]

Lucky Man ! Good find !!
Sorry for the questions

What year engine ?
Did you disassemble the oil pump and replace the piston?
What are the oil change intervals ?
Did you pump oil through the crank to see if the number 5 oil feed is blocked ?

[Ramage]

BL92

Yeah, I was very lucky to catch it before it caused major damage, after I took the bearing off the #5 cylinder I was shocked the crankshaft journal was not damaged.

What year engine ?

2004 08/04 Build date

Did you disassemble the oil pump and replace the piston?

I did not disassemble to oil pump, in fact I left it attached and worked around it, I am now hoping I am not going to regret not pulling the oil pump out and inspecting it.

What are the oil change intervals ?

I have owned the car since 2012 and it had 87000KM on the clock when I bought it. The car had obviously been abused so I got it for $15K Canadian (was a former California car) with the intention of fixing it and selling it on for a better example. After I started working on the car I decided I was going to keep it and just fix it up. The number of screws I am still finding missing is simply mind boggling, all that is to say I think it had a rough life early on and when I rebuilt the vanos the caramelization of the engine confirmed that. Under my owner ship the oil is changed once a year or every 5000KM.

Did you pump oil through the crank to see if the number 5 oil feed is blocked ?

I did spray a ton of brake cleaner through the oiler on cylinder #2 while I had #5 removed and the oiler on #5 was flowing "fine". Being honest I did not even think about where all the sacrificial material went from #5 until I read your post. So again I am hoping I do not end up regretting that.


The car is all back together and running good without any noise. Going to pull the oil out in 1000KM (if I do not hear anything before that) and have it tested.

[Ramage]

The good news.

At 1,000 miles (1,600 km), I changed the oil and filter, and found no shiny debris in either. Yay!

The terrible news.

The #5 rod bearings definitely spun at some point. I was so relieved to have "caught" the damaged bearing that I focused on the crank journal and the bearings' condition, overlooking the back side. Last Saturday, after changing the oil and sending a sample to Finning Canada for analysis, I watched an old RoadKill episode showing the back of a spun rod bearing from one of their project cars. My heart sank instantly—I couldn’t recall checking the back of my bearings.

Living in a condo, I do all my wrenching at my in-laws' garage, where I’d left the bearings. I rushed to inspect them, and sure enough, I confirmed what I saw: undeniable signs of spinning.



The bearings have spun, but I'm cautiously optimistic that I might have dodged an even bigger bullet than I realized. Granted this might all be just wishful thinking, but here's my reasoning.

The car has clocked over 2,000 km with these new bearings, and I haven't detected any rod knock.

My theory (and hopeful speculation) is that the bearings spun inside the rod, not around the crank journal, perhaps only a few times before stopping.

Why do I believe this? The wear on the unoiled backside of the bearings is minimal, despite the intense forces at play, and when I removed the rod cap, the bearings remained on the crank journal, still perfectly aligned as if secured by the rod, with the locating tabs mostly intact.

For now I am waiting to see what the oil analysis comes back with and being 100% realistic it is very unlikely I got away with just replacing the bearings on #5 and the knock will be back, but I can dream.

Wish me luck.

[sapote]

I think both crank journal and rod are damaged. Pictures of the crank journal and rod in good close focus?

[fattycharged]

No free lunches IMO, it spun and will fail again. I remember doing the same on an R32 a couple decades ago, I got roughly another 25k on that engine before it failed gloriously


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[Ramage]

I think both crank journal and rod are damaged. Pictures of the crank journal and rod in good close focus?

Thank you, that's really encouraging! 😊

Regrettably, I didn't capture photos of the crank journal or rod during disassembly. I wish I had, though, as you know, photos aren't great for evaluating surface finish.

I'm roughly 85% certain the crank journal is fine (I was completely sure when I put it back together). I closely examined it while cleaning the oilers, and it appeared flawless. Maybe it ovalled, but my plastigage measurements showed a steady 0.050mm clearance across all cylinders.

In the late '80s, I assisted a friend with replacing rod bearings on his 5.0L Mustang. Stranded in a remote area without a machine shop, we chanced using a slightly scored journal. That bearing failed again after only 50 miles—definitely not a fun experience.

This engine might be a ticking time bomb, but I’m hoping for some luck. If the oil analysis looks bad, I’ll likely pull the engine for a winter rebuild project.

A 3.4L stroker could be fun.

[Ramage]

No free lunches IMO, it spun and will fail again. I remember doing the same on an R32 a couple decades ago, I got roughly another 25k on that engine before it failed gloriously


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Man if I get 25K miles I am sold, I drive this car like 3100 miles a year so that is 8 more years of driving All my experiences with half assing bottom end rebuilds has resulted in pretty much instant regret so hearing about someone getting 25K is actually encouraging. Thanks!

Seriously if I can get a couple of years of normal "trouble free" driving from this engine as it is now that would be awesome. I will have my shop built and can work on rebuilding it without the pressure of being in my in-laws way.

[sapote]

When a bearing shells that overheated, expanded and grasped on the crank journal, tight enough to spin around the rod, then the shells and crank had been rubbing, metal to metal, for many revolutions, then the journal can't be flawless. The same for the rod surface.

[Ramage]

When a bearing shells that overheated, expanded and grasped on the crank journal, tight enough to spin around the rod, then the shells and crank had been rubbing, metal to metal, for many revolutions, then the journal can't be flawless. The same for the rod surface.

I appreciate the feedback, but I disagree with using "CAN'T" so casually. Anything’s possible, don't be a killer of dreams.😁

I received the oil analysis from Finning, and it shows elevated Lead and Copper in this 1600km sample. I’m not overly concerned just yet, as the new bearings now have over 3200km with no knocking during cold starts. The elevated levels could be residual from the previous bearing failure, or possibly the new bearings settling in (though that seems unlikely since they shouldn’t be making contact, despite what some online sources claim). Alternatively, it might indicate a bigger issue, so I’ll keep monitoring. Stay tuned.

[Gt4]

When a bearing shells that overheated, expanded and grasped on the crank journal, tight enough to spin around the rod, then the shells and crank had been rubbing, metal to metal, for many revolutions, then the journal can't be flawless. The same for the rod surface.

Will the tolerance changed if measuring the new bearings with Plasti gauge on a crank/rod surface that had spun bearing?

[Ramage]

Will the tolerance changed if measuring the new bearings with Plasti gauge on a crank/rod surface that had spun bearing?

Although the question wasn't directed at me, I can share my observations and experience. Plastigauge is only marginally better than doing nothing. As I mentioned earlier in the thread, my Plastigauge results were consistent, even on the cylinder that spun, but this might be due to where I placed the strip. If the rod’s big end was rounded or the journal was ovalized, rotating the crank half a turn could have yielded different results. I didn’t test this, so I can’t say for sure.

I’m taking a chance by assuming it’ll be fine, and the oil analysis will either help verify that or confirm things need to be done right. Since my M3 is just a toy and not my primary transportation, I am ok with taking the risk for now because it is not convenient for me to take over my in-laws garage for a few days to open it up again to check on the status of the bearings / crank. That said, I’d be frustrated if I end up with a new window installed in the block that could’ve been avoided by being more thorough with the bearings when I did have it apart.

sapote advice reflects the conventional wisdom on spun bearings: pull the crank, machine it, measure it, and fit new bearings to match the updated journal clearance. I don’t dispute this approach. However, after realizing I had a spun bearing only after I had already simply installed new bearings, reassembled the engine, and called it done. I figured I could document how that works out for me as there are many engines that continue running for thousands of miles after a spun bearing with only having minimal or no effort beyond replacing the bearings done.

[sapote]

1) Although the question wasn't directed at me, I can share my observations and experience. Plastigauge is only marginally better than doing nothing. As I mentioned earlier in the thread, my Plastigauge results were consistent, even on the cylinder that spun, but this might be due to where I placed the strip. If the rod’s big end was rounded or the journal was ovalized, rotating the crank half a turn could have yielded different results. I didn’t test this, so I can’t say for sure.


2) sapote advice reflects the conventional wisdom on spun bearings: pull the crank, machine it, measure it, and fit new bearings to match the updated journal clearance. I don’t dispute this approach. However, after realizing I had a spun bearing only after I had already simply installed new bearings, reassembled the engine, and called it done. I figured I could document how that works out for me as there are many engines that continue running for thousands of miles after a spun bearing with only having minimal or no effort beyond replacing the bearings done.

plasti
1) Installed new bearings: if not using plasigauge to check for clearance then how do you know how far off the clearance is? It's one of most importance measurement in rebuild engine.

Plastigauge is designed to be used on a round journal and bearing. Although we don't know your crank journal round or oval, but at least the plastigauge should be used to check at the position of the power stroke - about 45* after TDC as it's the max wear under max piston force.

2) If it's my car, at the minimum I would check or oval, polish the journal using strips and paste to mirror shiny, with crank in engine.

[sapote]

Will the tolerance changed if measuring the new bearings with Plasti gauge on a crank/rod surface that had spun bearing?

Assuming the seized bearing journal is no longer smooth and polish, the plastigauge reading is not accurate as it should be. It should be used on a poslished journal for a correct reading.