Piston Ring Question

[Threeofnine]

This is a sheer curiosity question. Do piston rings make contact with the cylinder walls or does oil prevent metal to metal contact? I just can’t see how rings can seal without metal to metal contact. And if there is metal to metal contact, how are rings not worn out extremely quickly? If oil does prevent contact, why is there not a lot of smoke and oil consumption?

 

[Trav]

This explains it better than I can.

Piston Rings, Oil & Cylinder Wall Finish - Engine Builder Magazine

A piston ring package is not only a seal for compression, it’s also controlling and distributing the oil on the cylinder walls of the block. The way a ring interacts with oil and the bore finish is critical to engine efficiency.

www.enginebuildermag.com

 

[jhellwig]

Smart assed and is yes no sorta kinda not really but yes. Travis answer is better though. All engines burn oil and no seal on a moving surface is 100%

 

[oil pan 4]

There's usually about a 1 to 3 micron oil film between the bore and ring.
The oil appears to prevent nearly all contact between the two surfaces.
The top of the bore where the top ring stops sees the most wear.
With your clearance being 1 to 3 microns means, Dirt = bad .

 

[JimPghPA]

There are different methods of making pistons, cast, cast eutectic (10 to 12 % silicon or more), and forged. The cheapest and most common is cast, and those expand the most when heated. The (gap) has to be there to allow for that expansion. How much gap is the question? I do not know. But some really is required, espically with common forged pistons.

 

[hpengineprep]

This is a sheer curiosity question. Do piston rings make contact with the cylinder walls or does oil prevent metal to metal contact? I just can’t see how rings can seal without metal to metal contact. And if there is metal to metal contact, how are rings not worn out extremely quickly? If oil does prevent contact, why is there not a lot of smoke and oil consumption?

You have two types of rings on a piston. Compression rings and oil control rings. The oil control rings are the third usually and they consist of two thin wipers, a spring, and drain holes behind the rings. They also float on a film of oil but most of it is directed through the drain holes. Only a thin layer of oil remains on the cylinder wall but it is enough to prevent metal to metal contact.

 

[Exhaustgases]

If there was no contact there would be no break in.

Did I pass?

 

[hpengineprep]

If there was no contact there would be no break in.

Did I pass?

You passed