What is ring seat?

[Bolts]

I know that when an engine breaks in, it is said that the rings seat.

I believe it must be related to the bore surface smoothing out so the rings run against a smooth surface (not sure).

I noticed carbon buildup in the piston ring grooves, mostly in the compression groove.

Here's my question.
Is carbon buildup in ring grooves really a good thing? Does the buildup under the compression ring increase the pressure of the ring against the cylinder wall and thus form a tighter seal? Is this when the rings seat?

Or is there no relationship to carbon buildup and the rings seating?

Thanks

 

[JSeery]

Carbon is a negative thing and not related to the rings seating in. Ring seating refers to the rings and the mating cylinder wall surface wearing to fit each other.

 

[flatheadmurre]

A piston ring isn´t square it´s shaped like a barrel, scraper etc.
From the beginning it has a very narrow contact surface against the cylinderwall breaking the oilfilm.
During break in the piston ring contact area wears getting a bit wider and both cylinderwall and rings get the desired finish.
The reason you need to run the engine under power during break in is to get enough ringpressure to break the oilfilm.
If the rings fail to break the oilfilm you can get a coating of the cylinderwalls(glazing).

 

[A bones]

Carbon is a negative thing and not not related to the rings seating in. Ring seating refers to the rings and the mating cylinder wall surface wearing to fit each other.

Times two, bang on. The problem with carbon ( burnt dirt ) is it can change the clearance room in the piston lands. When this happens the rings can not maintain their up-down travel path in the cylinder. At TDC compression the piston changes direction. The moment of reversal (up-down ) is accompanied with an explosion. The resulting vibrating forces can rattle the rings from their up-down path and allow the pressures slip by.

'Back in the day' An old Ford is left at the local service station with the complaint of "it smokes too much". Test drive shows oily smoke under acceleration. An indication of ring blow by. The old guy drains the oil, replaces it with kerosene, then parks it out back, running and smoking. After near an hour the smoke dies down. The kero is drained and clean oil put in. Then test drive. All is well.

The buildup of dirt, due in part to dried out steel-mesh oil filters , unpaved roads, less than optimal fuel, ign., etc. etc. the crud now lays in the drain bucket. The rings can maintain their up-down path, and seal, while the piston works to contain the forces and pressures of combustion.

The need of break-in (running fast) is rewarded with a higher-rate oil splash lubrication and yes, maxx pressure, to ensure the rings sit properly in the lands, during direction change, as the rings are learning the ropes of honed cylinders. As mentioned by Bolts a mating surface is made.

JSeery I gotta say, thanks for alllll you do.

flatheadmurre, I see your post about glaze. Again, I'm obliged to look to dirt. The glaze is not the oil, its the oil plus heat, plus dirt=scum. Another interference against the fitted up-down path the rings need. Please don't get me started on dirty or lack of dirty oil. I began my day for, more than thirteen years full-time, pulling drain plugs out of hot, abused, and neglected daily drivers.

 

[rotorwrench]

Carbon in the cylinder is a by product of all things that inter the cylinder from fuel mix to oil that gets past the rings. Piston tops and top compression rings can get pretty hot and any oil residue or excess unburned fuel residue will get baked into carbon there. Back when fuel was still containing tetra ethyl lead, they used to have more lead deposits to deal with but with no lead fuel, it's other additives that get built up in there. Excessive carbon usually indicates blow by which you can't really ever get completely rid of. No matter how good the rings seal, there is always a bit that gets by.