Do rings rotate?
 

We had an interesting discussion today at the swap meet regarding ring gap, and the question came up whether spacing the gaps made any real difference, because they rotate anyway. One thought, if they don't rotate, and like many gaps, it doesn't close all the way up, wouldn't it leave a small vertical ridge as the cylinder wears? Anyway does anyone have any insight on this?

Re: Do rings rotate?
 

Rings are supposed to be installed such that the gaps don't line up from ring to ring. So if one ring tended to cause a ridge the other rings would cancel that out. That is, wear it off.

Re: Do rings rotate?
 

'because they rotate anyway.'

says who?

more fordbarn erroneobilia

unless you are in a tornado

Re: Do rings rotate?
 

I see no reason as to why they would not rotate. They are not pined in place. The actual question in my opinion is how much do they rotate.

As for how come we care about spacing the gaps, we do know with 100% certainty the negative effects of a gap from the top on the piston down the side.

Re: Do rings rotate?
 

well they may rotate slightly but eventually will wear in and kinda seat themselves, if they rotated willy nilly there would be no such thing as stuck rings and would have worn out piston ring grooves in the pistons.

Re: Do rings rotate?
 

http://download.ms-motor-service.com...958-02_web.pdf

Section 1.6.11 covers ring rotation.

Re: Do rings rotate?
 

In the 60's I overhauled an engine where someone had installed the rings with all the gaps in a straight line on one piston. That cylinder had a line of metal where the rings didn't wear it away. That's the only time I've ever seen such a thing, but does show those rings didn't rotate.

Re: Do rings rotate?
 

Rings do rotate. I saw it fairly recently in an 0-200 Continental that an 'engine shop' had supposedly overhauled. The engine was returned to that shop twice for low compression and excessive oil consumption which continued.
We jerked the cylinders off it and found them tapered quite badly and the rings were lined up on 2 cylinders within 10 hours. Straightened them out, new rings and balanced the new pistons as they were out quite a bit. Engine has been running fine for about 3 or 4 years now. Knock on wood.
Maybe the engine was stuck together with those ring gaps all lined up, but, I doubt anyone would do that. But, they never took the taper out of the cylinders so who knows.

Re: Do rings rotate?
 

Lots of good information here Mike, thanks!

Re: Do rings rotate?
 

Years ago, I asked this same question and came to the conclusion that ,no, they didn't rotate. What would drive the rotation? would it be CW or CCW would the upper ring rotate CW while the lower ring rotated CCW? Would one ring rotate faster than the others? Wouldn't the cross hatch prevent it? Until the cylinder wore ever slowly out of round? Once the cylinder is out of round, the rings couldn't possibly rotate.
Terry

Re: Do rings rotate?
 

Sorry, SeaSlugs, but I have to disagree. The rings will move a lot. The only way to prevent it is with a pin in the groove at the gap, which I have seen. I can't remember what engine it was, this was long ago, but I know it has been done.

And piston ring grooves will wear out from ring movement and they can become bell-mouthed. Although they can be machined square again and have a ring spacer installed, it is really time to replace the piston.

Sticking rings can result from overheating, fried oil, varnish, dirt or other Acts of God not understood by Man. Sometimes it is just plain magic. Maybe even ethanol in the gas, it does everything else. :)

Re: Do rings rotate?
 

Question! How come the ends of the the comp. rings are not "lapped" over to gain a 100% seal instead of having a ring gap? In other words, the ends of the ring would be lapped over each other and there would be no ring gap. Just askin'.
Terry

Re: Do rings rotate?
 

Motorcycle two strokes almost always had the pins in the pistions to prevent ring rotation. I think because they didn't want the ring gap to occur in the port area.

Re: Do rings rotate?
 

A guy I knew went to a tech school in the '60's. He had lots of time to play, so he built engines and mapped where the ring gaps were when assembled. Even run for a few seconds when torn down the gaps would be at a different place. The only reason for staggered placement is for initial start up.

Re: Do rings rotate?
 

YES! That was the engine. Thanks Jon.
I raced a two-stroke motorcycle back in the 60's and tore it down many times. I should have remembered.

One thing I do remember well about those days was when the chain broke under extreme acceleration and the end of the chain came whipping around the rear wheel and snapped me on the hinder like a wet towel. I coasted to a stop on the track. Standing up. Stood up for quite awhile after that too. :)

Re: Do rings rotate?
 

It's pretty common with aircraft piston engines to see a sudden drop in compression go away after a few additional hours of operation. It was always explained as several of the ring gaps lining up. This differs from a slow degradation, which is due to wear. Of course there's many explanations for sudden losses of compression, but absent other signs of serious issues (i.e. an engine suddenly experiencing severe oil consumption, or uneven values of cylinder head temps) we would just run the engine for 10 hrs or so, watch it closely, and retest; compression would always go back to normal after a few hours.

Re: Do rings rotate?
 

Childs & Albert makes step-gapped rings.

Re: Do rings rotate?
 

All two stroke engines have their rings pinned to prevent rotation (and to ensure they are installed correctly in the first place). Otherwise if/when they rotate the ends will get hung up in one of the ports and BAD things will happen.

Oops, see this was already mentioned...

Re: Do rings rotate?
 

Rings start to move around in cylinders as soon as the gaps find a worn area to move to....old worn, out of round cylinders can be found to have all ring gaps lined up......after tear down,a dial bore gauge should be used to determined if you need to hone for slight wear or a complete rebore is necessary.....

Re: Do rings rotate?
 

Please explain where does the force that rotates the rings comes from? Pistons cannot rotate. The cylinder does not rotate. So how is it you say the rings rotate in operation?

Re: Do rings rotate?
 

Ring rotation is explained in paragraph 1.6. 11., on page 37 in the link referenced above.

Interesting read.

Bob

Re: Do rings rotate?
 

No description of the origin of the force is provided.

I have torn down engines that I put together and the rings were always right where I put them.

See also Tom Wesenberg's comment.

Compressive forces are pushing the rings out toward the wall

I for one do not believe everything that I read. If I did then this entire forum would have to be taken as gospel.

The article states that rings are rotating 5-15 times per minute. If this were true then in 10K or less miles your piston ring lands would be all worn out.

The actual gap in a hot engine is negligible because the rings expand with heat and the gap is nearly closed, thus very very little compression is lost. The airplane story is a presumption at best

Re: Do rings rotate?
 

The piston will rock as it changes direction. Also if there is a slight twist in the rods, the pistons will rotate. No they should not be a twist in the rods, but you see it all the time in model a rods. I ques some one does not know you are suppose to check the rods.

Re: Do rings rotate?
 

The force causing rings to rotate is the same force that causes pistons to suffer wear in the ring lands. What do you measure on a used piston? The gap in the ring groves. Aside from sealing compression, rings also function like bearings. Since the piston is fixed in position, somethings has to give to distribute the forces and dissipate heat. That would be the rings.

Re: Do rings rotate?
 

Excuse me, but piston ring rotation in aircraft engines is not presumption. This phenomenon is referenced in maintenance literature published by both Teledyne Continental and Lycoming. The technique of waiting and rechecking is also recommended procedure. Google "aircraft piston ring rotation" and you'll find a lot of references, mostly based on real world experience, and several references from the engine manufacturers.

I don't want to get into a flame war over this - it's not that important to me - so this is my last post on the subject. Agree or disagree at your discretion.

Re: Do rings rotate?
 

Not only 2 strokes. Early 500cc singles like AJ's had rings pinned.

Re: Do rings rotate?
 

From what I've been told, it's the cross hatch honing marks that make the rings rotate.

Re: Do rings rotate?
 

I am certainly NOT speaking about Model A engines, but I can attest to the fact that there is significant turbulence in a 'wedge' motor dependent upon valve placement (intake vs exhaust), valve timing and cam overlap.

I built a car in '74-'75 (?) that sat on the pole for the 500 and the following 400 that had the motor built by Chevy engine guru Bill Jenkins, and he was adamant that the rings not only be pinned, but we also drilled the edge of the pistons outer perimeter to add force to the top ring to keep it sealed. I made a die injector in an attempt to trace the air flow in the top end, but it was touchy shutting off the motor in time to 'read' the die vs letting it run and loose the die 'stains'.

Re: Do rings rotate?
 

Rockhillwill, I THINK Grumpy's idea with drilling holes around the top of the piston was also to shorten the path for the gases to expand the rings so they seal better. Would be great on a race car that gets rebuilt often, holes would probably carbon shut on a street engine. I had forgotten he did that until you mentioned it.

Re: Do rings rotate?
 

while we are at it, let's take advantage of this remarkable product from Kale Co for our cars...
http://kalecoauto.com/index.php?main...u8QOkpPCL8XWo2

Re: Do rings rotate?
 

don't u believe it :rolleyes:

Re: Do rings rotate?
 

Yep, the fella I tore this particular engine down with worked at that mentioned engine shop [ Great world wide reputation also] at the time it was torn down and reassembled there. And, I have read both manufactures manuals. I've seen it on other water and air-cooled stuff but could not say how it could have happened or how the engine was assembled.
Its just one of life's little wonderments. As in many things in this life, there will be doubters, thats fine.

Re: Do rings rotate?
 

I torn down a Model T engine that I had put fresh rings and honed the cylinders. I know when it went together the gaps were staggered. When I pulled the pistons to do some work because of oil pumping (the cylinders had to much piston/wall clearance from the get go) , 2 of the 4 pistons compressing rings had the gaps in a row.

Re: Do rings rotate?
 

Thanks Mike for a wonderful article. This is one of the few that don't talk in technical jargon but in laymen's language. Gonna print it out for future reference and rainy day reading. My old memory is not what it used to be (confirmed DAILY by my wife....lol).

Re: Do rings rotate?
 

Here is a paper from the SAE on measuring something some of you say does not exist, But what do they know right! :cool:

http://papers.sae.org/900224/

Re: Do rings rotate?
 

High school automobile mechanics class, 1967. We had a rep from Perfect Circle Piston Ring Company give a Forum on pistons and rings. When he was asked about positioning ring gaps opposite when building and engine....."You can position ring end gaps any way you want, run the engine for 30 minutes and if they are still in the same position, I'll buy everyone in here lunch". FWIW

Re: Do rings rotate?
 

Re: Do rings rotate?
 

I gave a ring to the first girl I wanted to marry. She gave it back. The second girl wouldn't take it because she wanted a new one. I guess you can't rotate some kinds of rings..... ;)

Re: Do rings rotate?
 

Bob,
Nice hearing from you. We are getting 1/2' here in VA supposedly. You guys OK?

Rings rotate at the rate of 3.1416 times pie + the humidity divided by the number of red heads in yer Model A. (mine baaaaaarely move...

Stay warm, Clem
Divide by the

Re: Do rings rotate?
 

Coriolis effect? If so, I expect one of our South of the of the Equator friends to pipe in with observations that their rings rotated clockwise but now that they sold their car to some fellow in Fairfax, the rings now rotate counter-clockwise...