I've intalled them in crawler tractors, lawn mowers, trucks, chainsaws, cars, and pickups.....but I still don't know how they really work.

I've been told that the ring "rolls" in the ring groove as it travels in its cylinder bore, but what really baffles me is lubrication. On the down stroke, is all oil scraped or wiped, leaving the cylinder bore totally dry? It seems if this is so that ring metal to cylinder metal contact exists and this would cause excessive heat and wear.

Thanks for your help!

Boggles the mind!
If you really want to be amazed, you should see how they make rings.

I don't know all the answers but you have it right for the most part. How clean the cylinder wall is after the oil ring wipes down the bore is a function of the tension on the oil ring and the second ring.

Racing sets use low-tension oil rings to help lubricate at high rpms and cylinder pressures. The top rings have a sort of barrel face; the second can be the same or be sharply beveled.

Materials range from cast iron too stainless.

The rings do rotate around the cylinder bore, the two stroke motors are staked and do not move.

Shade,
I am going to a ring seminar that Hastings is giving at our warehouse. If I get any interesting info I will try to post it.
By the way Wally does not know what the H$#L he is talking about ! (just kidding Wally) http://www.chevelles.com/forum/smile.gif

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Bill Koustenis
Advanced Automotive Machine
Waldorf Md

WHAT!!??

Are you guys saying that the rings rotate within the groove in the piston (as looked down on the top of the piston)?

I find that REAL hard to believe! (at least as far as the top rings go)

During the compression cycle, the compression would hold the ring snug against the bottom of the groove. (or you wouldn't build compression)

During the firing cycle, the expanding gas would hold the ring down. (sealing against the surface of the bottom of the groove)

During the exhaust cycle, the movement of the piston upward (friction on the cylinder walls) would keep the ring down.

It's only during the intake cycle that the ring would go to the top of the groove. That transition would occur right at the TDC point. Friction with the cylinder wall would keep it at the top of the groove.



So, when and why would the rings rotate? It's not due to the cross-hatch honing. That is symmetrical in pattern.

If they rotate, why would it make any difference where the gap is positioned during assembly?

I could be missing something here, but I sure don't see it.

Wes.

Wes,
You got it ! I dare you to take a motor apart and find the rings in the same position as when they were installed. It has to do with the general design of the rings, and helps to keep the ring grooves somewhat clean. I really do not think it is a fast rotation, but it does happen. I am going to a piston ring seminar that Hastings is giving next week and I will add this to my list of questions.

By the way guys, I want to make it clear that I was just messing with Wally in the above post. He is a very good friend / customer of mine and I could not help but give him some grief. He has probably built more performance motors, especially marine ones than all of us combined and he does know his stuff !


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Bill Koustenis
Advanced Automotive Machine
Waldorf Md

Wes,
You got it ! I dare you to take a motor apart and find the rings in the same position as when they were installed. It has to do with the general design of the rings, and helps to keep the ring grooves somewhat clean. I really do not think it is a fast rotation, but it does happen. I am going to a piston ring seminar that Hastings is giving next week and I will add this to my list of questions.

By the way guys, I want to make it clear that I was just messing with Wally in the above post. He is a very good friend / customer of mine and I could not help but give him some grief. He has probably built more performance motors, especially marine ones than all of us combined and he does know his stuff !


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Bill Koustenis
Advanced Automotive Machine
Waldorf Md

Wes, I know it sounds like a load, but think of it this way. They stake the rings in two stroke motors. There is a little stud that keeps the rings in place. There is a good reason, the cylinder has what they call finger ports so the fuel and oil can enter the combustion chamber. No valves like we know them. If the rings don't rotate, then why stake them??

Wes, I believe the only reason you place the ring gaps at assembly in certain positions, is so that you don't have any gaps in-line with each other at initial startup. This could cause the cylinder wall to get scared, and then the rings would not function properly ie. rotate during normal engine use. I rebuilt a Johnson 90 HP outbard motor a few years back, and these rings are not allowed to rotate because of what Wally said. The ring gap cannot intersect an intake or exhaust port, or it's all over for that motor, plus the 2 stroke fuel lubrucates the rings all the time, unlike a 4 stroke. If you have ever taken apart a 2 stroke, you'll notice that the cylinders are almost always scared in a straight up and down fashion, even in a motor that was well lubricated. Hell, it makes sense. 4 strokes would'nt last long if the rings did not rotate a little bit. It's kind of like the rotating lifter phenomenon. What I would like to know is, how many cycles does it take for the ring to rotate 360 deg.?

I knew that there was going to be a "discussion" here.

As I understand it, lifters rotate due to the cam lifter surface not being parallel to it's center line (it's off by 1 1/2 degrees). I'll buy that.

I've no problem understanding the situation in two stroke engines and oil control.


But, I see NO reason (by design) for the rings to rotate. The ring groove is a smooth surface and so is the surface of the ring. If they were not smooth, they wouldn't seal against one another.

Sure, they move around from the original installation. Stuff just moves if not tied down.




I contacted Larry Ofrea (spelled wrong) of Valley Head Service and put the question to him. His response was the same as my thinking, that there is no "design" reason for the rings to rotate.

It will be interesting what Hastings has to say.




In an added response to the original post, although the oil rings "wipe" off the oil, due to the porosity of the cylinder wall, not all is removed.

Wes. (hard headed) Vann

[This message has been edited by Wes V (edited 04-07-99).]

It's probably not by design, and I don't see the rings rotaing all the same direction, and at the same angular velocity. If it was by design, then it would probably be part of some kind of marketing gimic to sell rings. Someone would try to use it in an add somewhere claiming that the faster the rings rotate the more horsepower you get, or some other similar line of B.S. Maybe the engineers knew the rings would move around, and decided that was better for the cylinder walls. Maybe they figured the gyroscopic action of the engine would rotate the rings in a corrolis type effect to improve cylinder life. How do you like that line of sh*t! I am a mechanical engineer, and as you can see I don't know the answer, I just think it's a very interesting topic. All I can say is that in this type of engine, I think it's better that they don't stay in one position.

[This message has been edited by ETD66SS (edited 04-07-99).]

Rings are lubricated pretty well because they glide on a film of oil much like a bearing does. In fact, the ridge near the top of the stroke is the result of the ring wearing the bore as the ring comes to a stop at the top of the stroke; zero velocity gives zero hydroplaning of the ring on the oil film and hence the wear. As for rotation, it is pretty much random and I think that cross hatch must play a part in it. I spent several years testing piston rings for an engine manufacturer and rings became pretty interesting. Too bad the job did not last!

I am also very interested in what Hastings says. Do rings rotate differently above the equator than below ??

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Okay, I'm going to take a blind shot in the dark because I KNOW I'm not even close to being a mechanical engineer. But if you think about the last post, he got me thinking. Water when removed by opening a valve turns turns like a tornado through suction. Tornados are created by two different air masses with drastically different tempratures colliding. ANYWAY, don't you think that the suction (and possably variant in temprature) could cause this? I'd assume that their is enough cylinder pressure to cause this (especially with a cam that has a lot of exaust overlap). I don't know if I'm making sense to anyone but that's what I was thinking. Go ahead and shoot it down if you want.

-Joe Y.

Here's my .02

The flame front across a piston is NOT completely symmetrical. Therefore the explosion, if you will, is faster on one side than the other. Therefore part of the ring on one side gets pressed down into its bore before the other side. As the piston moves, this can cause the ring to stick just a little bit, and it will rotate. Not to mention piston rock. Heck, we all know that forged piston tend to knock a little till they expand. So the same could be applied to the piston rocking in the bore. No matter what the clearence is, if it exists, http://www.chevelles.com/forum/smile.gif the ring is going to stick more on one side than the other. I use "side" as a general term, as we know that circles don't have sides. Sound good? I should become a politician.. http://www.chevelles.com/forum/smile.gif

--
Chris

Whew! I'm glad I found this out. To think of all the time I've wasted lining up the ring gaps as per the performance manuals over the years. Now I know, when building the next engine I'll throw in a handfull of sand to score the cylinders and prevent this ring rotation. One of these days I'll build the perfect engine, you'll see. tom (in a cloud of smoke and a HI-YO Silver)

Don't forget that some long rod racing applications actually pin the bottom and sometimes the second ring so they cannot rotate. This is because the wrist pin is forced way up in the piston to the point that wrist pin hole crosses a portion of the ring pack.

If a ring gap were to line up with the wrist pin hole there would be big time blow by. So we know they rotate and some say the rotation is an integral part of optimum performance. They will site if rings ever get "stuck" the rings are not functioning correctly and wear will be accelerated.

When you do the assembly stager them as per the manufactures recommendation knowing they will not stay there. And yes I think sometimes the gap on the first and second ring actually line up which is not good from a blow-by perspective but they continue to rotate and things self correct.

John

Hi guys,
Here is the promised info from the Hastings ring seminar. Sort of condensed but pretty accurate.

1: Rings DO rotate ! The are designed to do so in order to keep from wearing in one place on the cylinder wall, and to keep from sticking in the grooves. All three rings rotate at about the same speed, so it is still important to space the gaps when installing them. The tech person at the seminar could not answer the question as to how fast they rotate, but I got the impression that it is very slowly. There were a lot of guys asking questions and I failed to find out exactly what in the ring design makes it rotate.

2: Cylinder wall finish is very important. Basically with todays rings you need a VERY VERY smooth cylinder. A "plateau" finish is preferred. This requires a special type honing "stone" or "brush" type hone as a final finish. (we use the brush hones at my shop) It leaves almost a mirror finish. The rings are pre - lapped at the factory and really should not need any break in.

3: End gap is important but it is better to have too much rather than not enough. They told us that in Dyno tests, there was no measurable difference in power or blowby up to .040" end gap. The guy basically said it is not as important as most people make it out to be, and they have seen plenty of damaged motors from not enough gap, but none damaged from too much.

4: Cleaning the bores prior to assembly: The only way to properly clean a bore is with a stiff brush and hot soap and water ! Solvents such as varsol etc will not get the crud left over from honing out of the metal pores. He also suggested wiping down with white paper towels until the towels came out clean.

5: Lubrication - I was very surprised to hear him tell us that they recommend a mix of motor oil and STP or similar assembly lube on the rings for assembly. Most of us seem to steer away from a real "slippery" lube on rings for fear of them not wearing in properly, but if it is true that they are basically broken in at the factory, then more lube should be better as far as initial wear.

6. "Scotchbrite" pads. Basically, don't use them ! Keep them away from any engine part etc etc. He showed us some highly magnified pictures of rings that had been sent back to them for problems, and you could actually see small pieces of the "scothbrite" material stuck to the rings from someone cleaning the pistons with the stuff. He told us that it is some of the most abrasive stuff known to man.

7. The rest of the stuff he showed us was dealing with new materials for rings in the near future. Mostly steel instead of cast iron, due to it's strength. We also saw a VERY interesting tape on the manufacturing process. You would be amazed at how rings are made ! If anyone is anywhere near the Hastings facility in Michigan, I would recommend you do a tour.

If there are any unanswered questions, e-mail me and I have a contact I can call and try to get an answer.



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Bill Koustenis
Advanced Automotive Machine
Waldorf Md

Thanks Bill for posting this, very informative. But I think you forgot to ask the most important question of all, do the rings rotate in the opposite direction south of the equator? http://www.chevelles.com/forum/smile.gif

Pat

yes, during odd-numbered leap years. And, don't forget the effects of the eleven-year sunspot cycle. http://www.chevelles.com/forum/smile.gif

Tom

WOW what a great post proabaly one of the best that I've seen thanks for the info guess I'l throw away my scotch brite now.....