Piston wrist pin lubrication

[Mikel]

In most engines the main and crank journals are pressure-lubricated, but the wrist pins depend on oil spray, which I have to assume is far inferior in terms of lubrication, but also see the same forces from the pistons the rod journals get. How is it that these typically last the life of the engine?

 

[PAE]

Pressed or floating ?

In production engines they are usually pressed so nothing moves.

 

[ExWrench]

In most engines the main and crank journals are pressure-lubricated, but the wrist pins depend on oil spray, which I have to assume is far inferior in terms of lubrication, but also see the same forces from the pistons the rod journals get. How is it that these typically last the life of the engine?

limited range of motion compared to rods or crank

EDIT: also, when the oil rings scrape the cylinder walls, they oil the pins.

 

[Mikel]

Pressed or floating ?

Both really.

 

[Provience]

They don't do much and don't matter much when worn

 

[AgitatedPancake]

I agree on the limited range of motion mentioned by Ex. Per revolution, they only rock back and forth by the max angle of the connecting rod (not including piston rock).

But on the same token, I think the piston oil sprayers on modern engines add more focused lubrication as well as pulling heat out of the pistons

 

[Roktoy829]

Since they took the skirt off the pistons, you get cylinders worn out way before the pin.

 

[Quick & Dirty]

The limited range of motion keeps the relative velocity low. Early automotive and current small engines are splash lubricated on rod and crank bearings as well, which is fine at lower rpm than modern automotive engines run.

 

[woods]

EDIT: also, when the oil rings scrape the cylinder walls, they oil the pins.

This is how I understood they work.

Different Wrist Pin Oiling Styles Explained

Wrist pins have one of the hardest jobs in an engine, carrying tremendou

auto.jepistons.com

Good writeup there.

 

[WLDWUN]

limited range of motion compared to rods or crank

EDIT: also, when the oil rings scrape the cylinder walls, they oil the pins.

yup

and thew ones I have seen have a hole in the top of the connecting rod to drip oil down onto the pin

 

[total newb]

Most diesels have piston coolers/squirter noozles that spray crank feed oil right up at the back of the piston.

As others said the oil control rings scrape oil off the walls and feeds it to the inside pistons n pins.

 

[total newb]

Right down on to the pins

 

[YZRider]

Most diesels have piston coolers/squirter noozles that spray crank feed oil right up at the back of the piston.

As others said the oil control rings scrape oil off the walls and feeds it to the inside pistons n pins.

Plenty of connecting rods are drilled.

 

[total newb]

Yup

 

[total newb]

Heres another view. This is how most oe sbc/bbc pistons are made and why they break the skirts off when they get spun up to fast.

 

[arse_sidewards]

Less angular movement per second but way less surface speed because smaller diameter to the point where splash lube dripping in from the oil ring is fine.

2-stroke marine shit sometimes uses needle rollers between the connecting rod and the wrist pin because of the sustained high speed and lesser overall quality of lubrication available inside a 2-stroke.

Heres another view. This is how most oe sbc/bbc pistons are made and why they break the skirts off when they get spun up to fast.

And I thought Ford 300 cast pistons liked to lose skirts.



That's fucking terrible. The hole doesn't even go down onto the pin, just into the void behind the skirt. The oil ring picks up more than enough oil from the cylinder wall so I'm not even sure what the purpose of that is.

Most pistons have a hole from behind the oil ring directly onto the top of the pin so that as the piston picks up oil sliding down the cylinders whatever oil is in the back of the oil ring gets pushed onto the pin.