well you bought it up

regarding the rings..

heat makes any metal expand, the rings when the heat up expand... since the rings are held in place by the cylinders they have only one direction in which to expand... That is why there is a gap to begin with...

 

Playing devils advocate, because it's fun....

What about gapless rings? how is that possible then?

 

dont know about them

maybe they are made from metal that only expands in one direction...

 

But look - piston expands, gases are pushing them out and what, they STILL manage to meet at the ends?
I am not saying it is not possible - I am just trying to understand HOW and WHY.

 

im guessing the pistons and cylinder walls (sleeves?) and rings are all made out of different materials...

which by definition means they have different expansion rates..

 

I fully agree. But HOW the piston rings ends can meet:
- liners expand
- pistons expand
- rings expand in length but get pushed outwards
Can all this be overcome by the length expansion?
Do we have someone here who is good at physics and/or metallurgy + knows something about the engines and could explain that?
I keep asking since I first read what TTP posted few months ago and I still don't get it.
Same with the question: does it happen in untouched engine?

 

Don't know if it helps, but can't hurt:

http://www.stockcarracing.com/techar...ics/index.html

This supports TTP's stance:

http://www.aa1car.com/library/ring_end_gap.htm

Straight from JE pistons:

http://www.sytyperformance.com/je_rings.pdf

 

Cylinder liners - Made of steel, CTE is smaller than aluminum. Higher temperatures will increase cylinder diameter. Combustion forces will try to expand the diameter of the cylinder.

Pistons - Made of aluminum, CTE is higher than steel. Higher temperatures will increase piston diameter and open up ring gap. Combustion forces will increase piston diameter and compress the piston (perhaps even having an effect on the ring gap).

Rings - Made of steel, CTE is higher than aluminum. Higher temperatures will increase the diameter, circumference, and thickness of the ring. Combustion forces will push down on the ring and tend to expand the diameter and also increase the circumference.

If someone tells me cylinder pressures and temperatures, I can generate some real numbers on the change in dimensions of each of these components.

 

Gapless Rings either have notches that overlap or are made of 2 rings. Either way they allow overlapping of the ends so that there is room for them to grow.

I think I know what you guys are missing. Yes the Piston can and will Expand, but there is room for it to grow, as the ring slot is deeper than the ring's width. So as the piston grows, the ring just gets closer to the piston.

The Sleeves Don't grow that much, because they are cooled by 180* water in the jacket outside. So the rings have nowhere to go. The End Gaps get narrower.

 

Yes, the stock Mahle pistons are forged. Tomei did an article in Turbo magazine when the X first came out comparing the differences 4b11T to the 4g63T.

 

Thanks for trying to explain.
The "sleeves" grow that much I would say - pressure test the cylinder on cold and on hot engine - you will see.

 

Well, I have a feeling that it was the only place to say so.

 

so whats your point? you don't think the ring ends can touch?

 

That explains the effect of temperature, but do the cylinder pressures really high enough in these motors to squish the rings and force them to expand further?

 

My point is that it sounds almost impossible that the factory miscalculated the tolerances so badly.
However with the engines producing 150% and more of the original power it is a different story as they require some bigger tolerances.
Moreover, if the stock pistons are forged, aren't they supposed to withstand much more thus be harder to damage?
But STILL - how big the miscalculation had to be to make ring ends touch?