how are the pistons of a 4 stroke engine lubricated?

Answer 1

many different ways including targeted and non-targeted piston coolers off the main oil rife, splash lube, lower drilled hole on the rod to crank journal, saddle jet squirters off the crank bore, drilled passage up the rod from the crank end to the piston pin then around the pin to the top if the rod--that hits the piston.

Answer 2

The majority of engines (car and off-road) I have worked on have used splash lube for the pistons. The connecting rod bearings that are directly below the piston are pressure fed by the oil pump. The oil, after it lubes and cools the bearings, is always squirting out in all directions from the bearing. This is called oil "throw off". A good deal of the oil is thrown upwards at the cylinder and the bottom of the piston. This splash lubricates the cylinder walls and wrist pin. The excess oil is wiped down the cylinder by the oil ring. This oil drips back down into the oil pan where it is pumped back up by the oil pump, back to the bearings. Engines that burn excessive oil have worn rings (poor cylinder wiping) and worn bearings (excessive throw off).

I've seen race engines that were built too "tight" (too little bearing clearance). The oil throw-off was not enough to lube the pistons. So the bearings seized from being too tight, and the pistons scuffed from lack of oil.

Answer 3

By oil from the underside of the piston that is fed to the connecting rods, flowing through the holes in the oil ring. The oil ring (bottom) on the piston also scrapes off the excess oil from the cylinder so it does not find its way into the combustion chamber.

Answer 4

splash, squirt and scrape (some have rods with squirt holes, some just get splashed and all have rings that sit in a groove at the bottom of the piston that has holes in the groove to allow oil to come thru ad be scraped up and down the cylinder walls.)

Answer 5

By the oil rings.