Hi All:

    In another post, it is stated that the piston ring turns while the engine is running.

    When younger, I was told that the rings in a car engine do turn in the cylinder while the engine is running.  The wavy springs in the ring/piston set up was engineered to cause the ring to turn.  This was to induce an even wear on the piston and cylinder.

   I had a difficult time believing this then and still do!

  Any proof that the rings actually rotate or turn on the piston while the engine is running?

K&B 4011 does not have a pinned ring, K&B 61 does.   

What Brian said is very true. If the ring gap is in the exhaust port where you can see it you can rotate the engine one way and the ring will move one way. If you then flip it in the opposite direction it will usuall move the opposite direction.

There's a high degree of vibration and force in reciprocating engines that can cause the rotation. Ring pins on two-strokes are used for a reason. Unless you want to do a rebuild by having a ring catch on a port, it's best to utilize the pins!

Valves in four-stroke engines also rotate in use. There are some interesting videos put out by BMW during testing that show this, and it's pretty impressive to watch, really.


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...flipping it over for several minutes and noticed that the ring gap was gradually moving between the port bridges.

Noticed this last week when flipping my old McCoy 49. The ring rotated the same way whether I flipped forwards or backwards.
I have had a few problems recently with this engine, this is why I was giving it some attention.

The first ringed engine I encountered with a pinned ring is the ST G.51. The K&B .40, ST G.61, ST .60bb and Fox Eagle .60 had rings but none were pinned. The deal there was that the port windows were interupted with multiple 'posts' to prevent the rings from 'hooking'. Blocking the intake side is going to reduce power a lot, but exhaust side isn't such a big deal. Having taken the T&L G.51 apart a few times, I assure you that the pinned single ring made it a big PITA...mostly because the sleeve is a heat shrink fit into the case.

Lauri, are your cylinder/case fits that tight? I can't for the life of me fathom the logic of honing the cylinder to get it dead round and the desired taper, only to shrink it into a cast case that's only bored and could easily be .001"-.003" out of round...remembering that the production machinery is likely old and may well be far from state of the art.  Steve

Lauri,
You seem to be talking of a very small number of very high tech engines. From Brown Juniors to the current production ringed engines, unless the rings are stuck or pinned, ALLl the rings rotate when run. Frank, I am sure, is not talking of a few super high tech engines that you are making. Your diatribe about poor old fashioned ringed engines may be perfectly true, but it has nothing to do with the question. I think you are inadvertently high jacking the thread!

Andrew.

Well Andew,

I have given my opinion and some practical examples to the question if it is good that ring turns. Why would you call that hi-jacking the thread? My time is limited so I tend to do things as well as possible, in the end doing so saves a lot of time. Of course we are capable of doing things that are not possible in mass production, I am very sorry for that.
But if they turn, why? A few possible reasons:
-Honing pattern may have an effect.
-Ring and piston side pressure is not symmetrical, and it's changing all the time. And same with temperature.
-The forces that compress the ring against groove walls are not symmetrical and of differend strenght in differend parts of cycle.
With those and propably several other things, you don't need much to trigger rotation. Why do loose screws turn under vibration?

L

Hi  Yes  most all rings move if they are not pinned, one thing that cause this is the cylinders  are  NOT   round when running, you have  a cool side where the cold fuel charge is coming thru, and you have a hot side of the piston and sleeve where the exhaust is, you also have cool air on 3 or so sides and 1 side ,or more, runs hotter, as soon  as the engine shuts down and cools, the metal will go back to normal size, another thing that causes  rings to turn is the cross hatch cut into the sleeve. I see this a lot when flipping  a non running motor, and it seems to move much more when the sleeve is brand new. they will also move  with new sleeves when running an IC engine in with an electric motor. A few times after much run times  I have seen motors have still rings that stay where they are.
Spinning rings are not much of a problem , and you have  no worries with sleeves that have smaller  window ports, large ports have to have the rings  pinned.

Randy

I would have thought that all 2-stroke piston ring grooves would have a peg in each one away from the exhaust port (and transfer port) in order to prevent the ring rotating in the groove and subsequently fouling the port.

Every 2-stroke motorbike engine I've come across uses this method to keep the rings in one place!

I'm surprised these aeroplane engines don't sustain extensive internal damage without this preventative measure in place.


Enlightened somewhat,


Tim

Tim

Most all model engines that do not have pinned rings have  window ports cut so they are small enough that the ring ends cannot get into the port, the loop charged engines with much larger ports are pinned so the cannot get into the ports. Many of the use either a very small roll pin, or a steel peg.

Randy