How do crankcase bearings work?

[@LubricationExplained]

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[@chippyjohn1]

Compression stroke, the stress is still on the top of the bearing until it reaches TDC. The intake stroke has the stress on the bottom.

[@yhseo3649]

Amazing explanation. I should've taken your lectures back in my university period.

[@LubricationExplained]

Wow, thanks!

[@blkros36561]

Best explanation I have seen on this. Thank you!

[@LubricationExplained]

Glad to be of help!

[@Woodstock258]

Very informative presentation of the crankcase crankshaft

[@LubricationExplained]

Thanks Alex!

[@simonm7776]

Another fabulous description. Thank you!

[@LubricationExplained]

Thanks Simon!

[@john24443862]

Thanks for your great explanation. I’m putting a diesel engine back together for my first time ever. What is interference fit measured by? How much interference? Fitted new piston shells on the new crankshaft. When fully torqued it can with effort be rotated (3 piston engine without head on, diesel). However, main bearings with new shells when torqued stop any crankshaft rotation at all. Even before being fully torqued. The supplier of the shells said because it’s a new crankshaft the shells can be standard. To me as an amateur it seems way too tight. Can you confirm that I would be needing or it sounds like I need thinner shells? I’m taking this really slowly to assemble as I have no rush. I live in the middle of nowhere where in Canada with no support for 60 km. The engine is for a John Deere dozer 350 1971 (ish). Any thoughts would be gratefully appreciated. John

[@rileycopple7896]

Hey can you comment on what the near future looks like for fuel shortages? I’m hearing a lot of rumors the east coast of the United States is running out of diesel fuel and it’s really concerning for us in the trucking industry

[@LubricationExplained]

That’s a great question but to be honest I’m not a specialist in the fuels industry. I don’t believe there are too many problems in the diesel supply chain at the moment. On the engine oil side I know one of the two major additive suppliers is out of CK-4 additive for the foreseeable future, so that it a bit concerning. For the moment it seems the rest of the market is picking up the slack.

[@chippyjohn1]

My understanding is a journal bearing works on oil being drawn into the area of most pressure by surface friction between the journal and oil viscosity. I am trying to understand what the correlation is between the speed of the bearing (circumference m/s) and the force being applied for a given viscosity. There must be a table or formula for force, speed and surface area as to what load a specific viscosity can maintain separation between the two surfaces.

[@stevenroche9874]

Gasoline burns very rapidly, diesel fuel explodes in the combustion chamber. That is why diesel engines produce a knocking sound while running.

[@averyalexander2303]

Great explanation! Since there's not supposed to be any metal to metal contact between the bearings and the crankshaft once the engine is running, would it be reasonable to say that most bearing wear is caused on startup before the hydrodynamic wedge is established and by contaminants in the oil?

[@Robert-pq3sb]

So in a big end bearing. The oil is in between the shell and the crankcase? So the shell is interfered into the block?

[@grein545]

Could you do a video on the role of bearing coatings? An example is the upper bearing on the BMW b58 engine has a special coating that supposedly protects the bearing from the extra wear associated with the start/stop system.

[@85932]

Thanks.....

[@LubricationExplained]

You’re welcome! 😊😊

[@MunsKi]

is it true that diesel engine oils have more zddp compared to motorcycle oils?

[@averyalexander2303]

Sometimes, but not always.

[@franzliszt3195]

Dam, that's a lot of variables

[@LubricationExplained]

Hahaha

[@camillosteuss]

I get all of it, and its very well put, but the embedability kinda fucks with me here... I am not a stranger to the concept, and its used by machinists to form lapping surfaces, be they cylinders or plates for honing... Either way, it reminded me of a video that had Stefan Gsw. talk about german humor... He mentioned a machine that used plastic bushings, was it teflon or uhmd plastics, i dont remember, but the machine used plastic bushings and precision ground chromed, tempered steel shafts in those bearings... The plastic bearing is what you would assume to wear down if it should be contaminated by getting embedded with grit and shit... But no, its the ultra hard, chrome plated shaft that wears down like a stick of turd and the plastic bushing outlasts the shaft... Why is it so? They put a shaft in the bearing, let mud and grit drip over a fresh prototype example and observed the wear pattern... The ultra hard shaft, like the crankshaft, of course, does not take in the grit, and it gets embedded into the bushing, but that is it, the bushing is pliant enough that it sucks in the grit particle that oil cant wash away and it stays there, not damaging the bushing any more, but every single time the shaft makes a rotation, it gets scuffed by the particle... And the more particles there are embedded into the bushing, the more effectively the bushing is converted into a shaft hone that eats away the shaft with each second while not suffering any damage beyond having its surface now not as precise as manufactured, given that it took in the grit particles... Its a very stupid property in this case, because if the crankshaft is ``more embeddable`` than the bushing, then it will take on the grit, and will not really loose precision, but it will then become a bore hone which will eat out the bushing(bearing) in a few seconds of working, as it will scratch the bore of the bearing... If the bearing is more prone to it and gets embedded with grit, it will as said, become a shaft hone and will grind down the crankshaft in seconds without wearing itself... If the bearing is abrasive, your crank is gone to shit, but if the crank gets abrasive, it will eat any bearing and contaminate the oil in every moment of its rotary motion, making you have to regrind the crank to remove the grit from the surface of it, even if its dimensional measurement and geometry is perfect... In both cases you as the guy who owns the rotary assembly are fucked... When you are a machinist, its a very nice property, allowing you to ``charge`` the surface of a plate or a bore or a shaft with say diamond particles against a very hard surface and then use that as an abrasive ultra precision tool, but that comes with knowing what hardness is the material its used against(utilizing embedability twice, once to charge a tool, then to make sure the tool wont contaminate(charge) the work piece itself, but will only grind it with precision)... Embedability in bearings doesnt make sense as a consideration... If the bearing and the crankshaft were hard as diamonds but not as brittle, and so then it would not allow any particle softer than diamond to embed into either, but would crush the particle by sheer force, and as said, if it was as hard, but not as brittle, the system would then work as good as possible, and would not risk either component becoming a grinding tool during work... But that is a machinists fantasy... A material that is both incredibly hard and rigid but durable and able to resist impacts and sudden stress... Also, then it wouldnt technically be considered ``embedability`, as you would be using both a shaft and the bearing of the same hardness and lack of embedability to avoid charging either surface with grit, but you would want to utilize the miracle material to batter any particle into submission... The ``healing`` of the surface could occur, but the particle would have to be absolutely minimal but just above the oils washing capability... Its really a stupid approach as no surface once charged, however plastic or elastic or plaint it is, can be used to negate the fact that it ate up a particle of grit... just by being worn down it will always again and again reveal the grit particle.... Its a good idea in theory, but i dont see it really working in such an environment... The particle is either small enough to wash away or big enough to be charged into surface and from there on, the surface wont get perfectly healed and as it wears, that ``healed`` layer would have to reform constantly, taking material away from somewhere, but that particle too would stay there and its much harder, so it would eventually surface when it could not be pushed in harder and covered... I dunno, as a machinist, it kinda doesnt really sound 100% on point here in this case to me... It would have to be a miracle material once again, but this time soft and yet not soft but rather seemingly soft due to its plasticity...

[@KarolosAthens]

Polar diagram of pressure '

[@LubricationExplained]

Hopefully a helpful visualisation…

[@jay_321]

Nearly all automotive crankcase bearings are plain bearings but nearly all small displacement motorcycle crankcase bearings are roller bearings or ball bearings. Why is that?

[@mareksumguy1887]

Street bikes use plain bearings because plain bearings have less friction and last a lot longer. Dirt bikes are more likely to suffer from oil starvation/surge. Roller bearings are far more tolerant of momentary oil starvation than plain bearings.

[@nowayjose596]

There's a problem with your visuals that may make this confusing to viewers - you're showing the two halves of the bearing fitting directly to the crankshaft journal with there then being a small space between the bearing and the connecting rod/cap (ostensibly for oil to flow through). This is incorrect as the space for oil to flow is between the bearing and the crankshaft; the bearings fit directly to the connecting rod/cap. I know you obviously know this and your audible description of the relationship is correct, but it doesn't match up with how it's shown visually.

[@AEVMU]

My fake hips are ''self healing'' as well. True story. BHR resurfacing hardware. Not sure what viscosity my body produces though.