What Is A Spun Rod Bearing - Explained

A spun rod bearing or main bearing is caused by lack of lubricant or excessive head, and will cause an engine to knock before it finally seizes. Don’t neglect your oil, don’t let it run low, or ignore the engine oil light.
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[@610610billy610610]

When i was 17 i spun all 4 rod bearings in my celica being dumb. They were destroyed. 17 year old me didnt know better, so i bought some nice rod bearings, put them in through the oil pan, cranked them down with no torque wrench, and was super proud lol. I started the car, it sounded like it had serious cams in it. "Brap brap brap brap brap" then it blew up again after driving it 100 feet lmao. Lesson learned. I learned a ton of lessons the hard way, but the hard way to learn is still a way to learn.

[@Motorcarnut]

Very true!

[@mondavou9408]

After all these years hearing the term, NOW I can visualize it. Thanks.

[@Motorcarnut]

Awesome! That was the whole purpose of the video.

[@Wi1dCatAZ]

Learned something new. Very well explained. 👍

[@Motorcarnut]

Thank you very much!

[@johannjohann6523]

This is exactly why I am "Not" a believer in low viscosity oils like 0W - 20. Heat in an engine causes the viscosity of oil to be reduced. Furthermore, high viscosity oil help compression and oil pressure. If you put a "full synthetic" (which is a blend of synthetic and mineral oil) 10W-40 oil your car, by the time you change the oil it is not uncommon for that oil to from a 40 weight viscosity down to a 30 or even 20 weight viscosity. I always like to look at racing for what is probably the best components and products for a car. In NASCAR they use a 100% Synthetic 10W-60 engine oil for racing for the reason I explained above. It needs to be noted though, 100% Synthetic oils do not have viscosity breakdown until usually 10,000-12,000 miles. And why you can go longer between oil changes with 100% Synthetic oil. Also, 100% Synthetic also leaves a film on engine parts that protect from "dry starts". I always say, if it is good enough for NASCAR, then its probably good enough for my car as well.

[@Motorcarnut]

Good write up! Many people can learn from this. Most of the problems new cars have is way too tight oil bearing clearances and lack of changing the oil results in a high amount of engine failures. BMW comes to mind with there 1000 of an inch oil bearing clearances, ridiculous.

[@mooosestang]

Same! I run 10w30 in my mustang that calls for 5w20. it's not stock though. maybe at stock power levels and normal driving 5w20 would be ok. I also don't drive it when it's below 50F outside.

[@frankandricciola9782]

The little tabs do not keep the bearings from spinning. They are locator tabs. It’s bearing crush and oil pressure that keeps a bearing from spinning

[@Motorcarnut]

You are correct! I misspoke on that one meaning exactly what you said.

[@frankandricciola9782]

No problem. Glad I could help

[@modifyman6977]

Could and would the machine shop address that seized/welded on bearing? Sort of grind it down and off. You use the term grind but I would imagine it's still a sharp tooling bit that cuts in a thousandth, or less, at a time. Would not want to risk breaking the tool/bit.

[@Motorcarnut]

No, that crank in the video is scrap.

[@Mr_Arvs]

Hi I think have a spun bearing with the rattle/knock at revs over 2000rpm. Can I drive it to the workshop about 10 miles away or will that further damage the engine?

[@Motorcarnut]

I wouldn’t, I’d get it towed.

[@migosyouknowmigos4219]

Can it damage the engineblock? i drove like 5min with a knock sound from a rod bearing i didnt knew it but then i turned off the engine

[@Motorcarnut]

Not likely unless the rod ripped off and hit the block. But that’s more rare.

[@mikeoutdoors4729]

Very cool, always heard of it but never seen it 👍

[@Motorcarnut]

Thanks, yes I wanted to visualise it.

[@jcrides1320]

You don’t want to see it :)

[@musicmojo100]

I can show you... took mine to a shop. got it back to notice a ticking sound that overtime became a knock. now the shop doesn't know me. T^T

[@damiropadobarglumskiperiod505]

I drove my car with low oil preasure(not constant low) for some 15 miles.i knew that will be thw end of that engine cos i had no other solution)engine is 1.4hdi with very high mileage.of course i had intention to buy other used engine and it is not much expensive.i have been searching for engine but after some time i turned my car on and there is no oil warning lighht(for now) and surprisingly no knocking sound you can say more or less it works ok.i do not have intention to work on it until spring time.if the bearing is not spining around journals and no major damage ond the cranshaft(maybe i have to change the rod bearing)is it worth of trying to repair or i just put other engine.

[@Motorcarnut]

It’s worth to try repairing especially if it’s not that bad yet

[@atomicdmt8763]

bearings NOT held in place by the tab. Its the crush strength that holds them.

[@Motorcarnut]

You are correct! I misspoke on that one.

[@kh2140]

What type and brand of oil and filter do you recommend?

[@Motorcarnut]

Depends on the vehicle. But Mobil 1 is a good brand for oil and filters

[@picksiauya]

Lets say youre tearing down a block. Can you reuse those crank and rod bearrings if they dont look domaged?

[@Motorcarnut]

Yes

[@Motorcarnut]

but I would re measure them to make sure they are still in spec.

[@lucaric6935]

Also what causes the connecting rod failure. Low pressure? Or over rev

[@Motorcarnut]

Both

[@lucaric6935]

@@Motorcarnut owners manual recommend change oil every 6000miles or 6month. But I accidentally change the oil once a year for last season. Big deal?

[@Motorcarnut]

No it's not. Just try to do it every 6K as stated. Also don't neglect the coolant system, should be flushed every 2 years to avoid problems.

[@lucaric6935]

@@Motorcarnut yes sir!

[@darrellsomers5427]

I diss agree over revving it won't take out a bearing ,its an oil problem or a machine shop didn't get it right

[@Peter-pv8xx]

I had installed a 305 Chevy engine in my 1979 Malibu classic sport coupe, the original engine was a 267, one day near home I decided to floor it, the throttle stuck wide open, I threw it in neutral and well you can guess what happened, it overreved. I then installed a brand new 350 Mr Goodwrench 350 then somebody stole the car, I got it back but it never felt the same, I loved that car, I bought it brand new.

[@Motorcarnut]

Sorry about that. I wonder why it didn’t feel the same? They dogged it when it was stolen?

[@Peter-pv8xx]

@@Motorcarnut It was trashed, the wheels with brand new tires were gone, the accel wires coil were gone, the battery of course the stereo the cb radio, all the CDs that we brought, the spare tire the jack, the steering column was destroyed the aftermarket cruise control I had installed was gone, the worse part was this occurred in Boston, I live in New Jersey, me and my girlfriend had gone on a dinner cruise in Boston harbor with some friends, I called the police from a pay telephone, this was in 1991 so no cell phones, they said that they don't send a police car just for a stolen car and said if I wanted to file a police report I'd have to come to a station, we got a taxi cab and told the driver to take us to the nearest station, I filed the police report then had to get a rental car, the only place was at Logan airport, we got another cab to the airport got a car then got a motel room for the night, I even drove around the area to see if I could find my car. We drove home the next day, my uncle picked us up from Newark airport, that night I get a call from Boston police telling me they found my car. I called my girlfriend who lives only two blocks away, I told her that I'm driving back to Boston tomorrow to get my car no matter what condition it was in, I had a 1981 dodge ram 50 pickup, I loaded all the tools I thought I'd need, I worked at an auto parts store, I went there and told them what happened, my girlfriend wouldn't let me go alone so she took off work, I think I drove 80 miles an hour all the way there, I think it took four hours to get there. My car was at a towing company sitting on the ground in Dorchester a suburb of Boston that is mostly black and Hispanic, the owner of the company helped me scavenge parts from other vehicles there, tires cap rotor battery a screwdriver to start the car, no internet back then so he had a Chiltons manual to look up the firing order, when everything was together my baby started right up, the guy who helped me would not accept any money for helping me, all I had to pay was for the storage the towing etc, I tried and tried but be refused any money, I had to drive the truck because it was a stick, my girlfriend drove the Malibu, I followed behind and after a while we pulled off the highway so I could ask her how the car was, she said there were no problems, after a while driving we stopped for something to eat, when we came to a toll she told them, no easy pass back then either, that the truck behind would pay the toll, we made it home around 3am, the next day I set about the task of putting my car back together, I had the factory wheels and caps which were painted to match the car, that's the way it came new, there was a bump in the floor behjnd the drivers seat due to the car being dropped onto a cinder block which damaged the body mount which eventually rusted out, that feeling of being violated like most people who have had their house robbed or their person assaulted for some reason the car just didn't feel the same, I did drive it for many years after but I had lost interest in it, maybe it was because I was older I don't know, she even climbed pikes peak when I drove to Colorado to visit my sister's.

[@Motorcarnut]

@Peter-pv8xx Wow, an amazing story. I feel for you and such great effort on you part and the people who helped you. Now I know what you meant by never felt the same. I would of felt the same way.

[@dpierson489]

You should have installed a 4speed, now days most people don't know how to drive a std and a kill switch helps.

[@akaitv6606]

Those tabs on bearings are to locate the bearings not to prevent spun bearings , bearings rely on cruch .

[@Motorcarnut]

Yes, correct!

[@brucesanderson9602]

Ok. I got one that is really eating my lunch. Bought 07 envoy. 4.2 in line 6. Me and a fella I know we're just sure. It was a rod knock. We were pizzles that fella said he drove it that way 300 miles. I tear down to oil pan. No small job...main bearings feel tight. Engine spins freely but there was a ton of metal that came out in the oil. I take off valve cover and sparkplugs. All look good. Another big job...... I take of front cover of motor to timing chain I still do not see the source of all the metal in the oil. My friend is now convinced there is nothing wrong in the engine........ I think there was too much metal in the. Oil for there not to be

[@Motorcarnut]

What about all the connecting rod bearings? There should never be metal in the oil, also can be a scored piston skirt.

[@Airman..]

Bearings could spun from normal wear and tear, contaminated oil, high rpms

[@Motorcarnut]

Contaminated oil and high rpms is neglect and not from normal wear and tear.

[@mooosestang]

Detonation

[@Airman..]

@@mooosestang under boost detonation will flattens rod bearings otherwise it can't happen an NA engines

[@mooosestang]

@@Airman.. ??? You can have detonation on a NA engine or are you saying it won't hammer on the bearings because it's NA? Some of these new engines have 12:1 compression ratio, crazy!

[@Airman..]

@@mooosestang only made possible by the precise timing of Direct injection, this system have strict safety knocking algorithms, slightest sense of bad fuel or bad fuel atomization will limit engine power before it kill anything, bearings in this case is the least of considerations. By all means static compression isn't as dangerous or destructive as dynamic compression aka boost in high performance engines

[@JuanRodriguez-yl9oq]

What are the main reason of loss of oil pressure?

[@Motorcarnut]

Oil pump failing or failed, engine just worn ( main bearings etc)

[@iipumpkiniix]

Using the wrong oil, Synthetic/Conventional ….. killed our 2000 Daewoo :

[@uranium3111]

@@iipumpkiniix My first car was a 02' Daewoo leganza and it locked up because at the time I was not aware that you needed to check or change the oil.

[@RoxusRemo]

@@uranium3111 Haha aw that sucks. It's sad how they don't teach the basics of stuff like this at school.. or your instructor didn't do a great job either lol.

[@cplpetergriffin1583]

@@uranium3111 how? thats car ownership 101. Thats like not knowing you should feed your dog

[@Xcelplus]

If lack of oil (lubrication) is the main reason that bearings spin then you can prevent this problem if you can bond a lubricant to both metal surfaces. 🙂

[@Motorcarnut]

Such as?

[@Xcelplus]

@@Motorcarnut XcelPlus

[@bigears4014]

Crap there are heaps of reasons, the main one would be conrod out of round

[@Motorcarnut]

But why? because lack of oil, oil starvation.They all come down to that.

[@bigears4014]

Journal to rod clearance not only oil , once the clearance is there the oil won't help anymore

[@Motorcarnut]

You’re talking about maybe incorrect rebuild, that misses the point of the video

[@THEROTTINGDOG]

No knocking but excessive vibration over 6k rpms, I was guessing this is what it is. I'll finish the teardown.

[@Motorcarnut]

Yeah curious on whats your problem, keep me posted.

[@THEROTTINGDOG]

​@Motorcarnut hand tight front sprocket and main engine mounting bolt. I still performed the teardown replaced all the gaskets and torqued everything on the way out like God intended. Runs like a charm.

[@THEROTTINGDOG]

1000cc kawasaki has too much power for hand tight anything.

[@Motorcarnut]

@THEROTTINGDOG Awesome!

[@darrellsomers5427]

If its a spun main bearing its most likely a junk block now

[@Motorcarnut]

Main bearing, then yes block is scrap metal

[@irmods]

It would be cheaper to just drop in a rebuilt engine depending on the mechanic.

[@Motorcarnut]

Not really, depends on many factors

[@markwiza3839]

Tabs do not keep a bearing from spinning

[@Motorcarnut]

Correct

[@jamesgrantham1352]

Yes they absolutely do. The tabs are positioned opposite each other and against the direction of rotation. They are not designed to withstand any catastrophic events, in fact engine bearings are engineered to be the first to fail in attempt to save major components. 🤓👍

[@bospet6453]

Tabs are only for alignment side to side Not to keep them from turning. The crush from torquing them down is what holds them from spinning.

[@Neploid27]

@@bospet6453 but the tabs do constrain that axis of movement, there is no argument to be made.

[@so4real]

They actually do. We removed one from a Mazda 6, after it started spinning freely.

[@dpierson489]

Don't run the darn thing out of oil!!

[@Motorcarnut]

Correct

[@stanparsonstreeinc]

Sand paper rope

[@Motorcarnut]

What do you mean by that?

[@stanparsonstreeinc]

@@Motorcarnut smooth the surface

[@Motorcarnut]

@stanparsonstreeinc if you can but most times it’s too far gone and crankshaft has to be replaced.

[@17th_Street_Preacher]

Had a spun rod bearing, put a new crank in, all new bearings & new rod..After 20min of road time it spun the same bearing😂 I did reuse the same old oil pump but is there something else that may have caused this?🎉

[@Motorcarnut]

The oil pump should always be checked but probably a blocked oil passage leading up to the failed bearing.

[@dgaz3057]

BS it can be fixed on the car...tons of videos that show it as long as you measure everything.

[@Motorcarnut]

And if it's out of spec? Most of the time it has to be removed, how are you suppose to remove the connecting rod or crankshaft? You should learn a little before passing clueless judgment.

[@dgaz3057]

@@Motorcarnut it's not clueless measure everything means just that... meaning if you can get away with the extent of the damage, it could be way out of whack. If it's out of spec then you have to pull the engine. I'm not going to get into this. When you make an engine repair without pulling a motor and if succeeds, the customer will be happy and you will save a ton of time.

[@Motorcarnut]

How are you supposed to measure a connecting rod bore for out of roundness in the car???? Guy like me are here to teach you only if you’re willing to learn of course.

[@iipumpkiniix]

Yes, you can R & R the bad bearing, but it won’t last …. Impossible to get the journal into perfect round while on the block.

[@Motorcarnut]

So what good is it?