Bearings - big end and little end

[Fresh Prince]

I'm trying to understand where bearings sit in an engine, and trying to understand whether big end and little end are connected in any way.

Am I right in thinking that they are connected by a rod at the base of the piston which goes up and down a cylinder, with the little end connected to the base of the piston, and the large end connected to the crankshaft? If you were to strip an engine, can you get to one without the other, or do you have to get to one to get to the other?

Please forgive my ignorance! Trying to understand in theory how these are connected.

[227bhp]

https://lmgtfy.com/?q=Connecting+rod

[M32Guy]

You are almost correct. There are no bearings, big end and small end refers to the ends of the con rod (connecting rod). Little end connects to the piston, big end to the crankshaft. Small end is connected through the piston via a gudgeon pin. Big end is half circle shaped and theres another half circle that then bolts on after its put round the crankshaft. There are two shells that sit between the two parts of the big end and crankshaft. These have a constant film of oil that essentially float the big ends off the crank. The shells take up any initial wear from normal use or if there's a lack of oil.

You would need to remove the piston to get to the small end and gudgeon pin. To remove the piston you will need to disconnect the big end from the crankshaft. Most pistons are removed from the top after removing the cylinder head

[hidetheelephants]

You're not going to get very far without a bearing in the little end.

[SystemParanoia]

[Boosted LS1]

hidetheelephants said:

You're not going to get very far without a bearing in the little end.

Depends on if it's an interference/press fit or bushed little end. :-)

[Fresh Prince]

M32Guy said:

You are almost correct. There are no bearings, big end and small end refers to the ends of the con rod (connecting rod)...

Thanks, this is very useful. I've spent the afternoon googling and trying to understand it but only with partial success.

So, you say there are no bearings, then when people say "big end bearing", what are they referring to? Is it just where the con rod meets the crank?

[227bhp]

Fresh Prince said:

M32Guy said:

You are almost correct. There are no bearings, big end and small end refers to the ends of the con rod (connecting rod)...

Thanks, this is very useful. I've spent the afternoon googling and trying to understand it but only with partial success.

So, you say there are no bearings, then when people say "big end bearing", what are they referring to? Is it just where the con rod meets the crank?

It isn't. It's of little use (like your attempt at Googling ) and is wrong, read this PDF here: http://kingbearings.com/files/Engine_Bearings_and_...

It is a bearing, they are bearings known as 'shell' or 'slider' bearings. The problem is as you will see that it isn't black and white (things seldom are) and it has to perform different functions in different conditions throughout its life.

Your next question may well be "Why don't they use roller bearings?", they do in motorbikes.

[Boosted LS1]

Fresh Prince said:

M32Guy said:

You are almost correct. There are no bearings, big end and small end refers to the ends of the con rod (connecting rod)...

Thanks, this is very useful. I've spent the afternoon googling and trying to understand it but only with partial success.

So, you say there are no bearings, then when people say "big end bearing", what are they referring to? Is it just where the con rod meets the crank?

Yes, it's a bearing shell that sits between the con rod big end and the crankshaft. Without the shell you'd wear out the big end part of the con rod. Shells wear out but are easily replaced. Think of them as cartiledge in between bones/joints.

[M32Guy]

Fresh Prince said:

M32Guy said:

You are almost correct. There are no bearings, big end and small end refers to the ends of the con rod (connecting rod)...

Thanks, this is very useful. I've spent the afternoon googling and trying to understand it but only with partial success.

So, you say there are no bearings, then when people say "big end bearing", what are they referring to? Is it just where the con rod meets the crank?

Well technically they are bearings but not in the sense you are probably used to such as wheel bearings etc. I've probably tried to over simplify it for you

[Boosted LS1]

Maybe they could be thought of as 'load bearings'. So in a wheel they'll be ball bearings etc and on a crank they'll be bearing shells.

[GreenV8S]

M32Guy said:

Well technically they are bearings

It's not a technicality. These moving connections absolutely are bearings, similar to many other bearings throughout the engine and the rest of the vehicle, and to say they aren't bearings is fundamentally wrong and misleading. Some types of bearing have rolling elements and some don't - they're all bearings.

[Fresh Prince]

Right I think I get it now, so the shells are bearings, just a different type to what I'm used to (normally ball bearings). Thanks all!

[M32Guy]

GreenV8S said:

to say they aren't bearings is fundamentally wrong and misleading

Which is why I've already clarified the point

[Mignon]

My head hurts.

[Mr2Mike]

hidetheelephants said:

You're not going to get very far without a bearing in the little end.

There are no replaceable little end bearings in the majority of modern four stroke engines. The gudgeon pin is typically a press fit in the con rod and the bearing surface is simply the hole in the piston that the gudgeon pin sits in.

Two stroke engines generally have a needle roller little end bearing as there is far less lubricating oil available.

[samdale]

Fresh Prince said:

Right I think I get it now, so the shells are bearings, just a different type to what I'm used to (normally ball bearings). Thanks all!

See also "journal" or "plain" bearing. Have a look at different types on Wikipedia.
They are just a very simple form of bearing.