Do the rings spin on the piston?

[greencrew]

In a normal operating engine, do the rings move or spin around on the piston as you drive down the road?

I ask this in relation to comments I have read here that talk about rings that get stuck in a groove. In my mind, if the rings don't get stuck in a grove it will move around in a perfect circle that will provide a better seal.

Please advise.

 

[Idrinkmotoroil]

I've had people tell me they aren't supposed to spin, but I have seen it myself on engines taken apart after short re-builds, the piston gaps are not set exactly the same way they went in which tells me the rings do dance around a bit.

 

[Ken2]

Very large diesels have a piston ring detector that keeps track of the rotation of the top ring. If it stops rotating an alarm sounds. It's interesting to note the different speed of rotation depending on the load...faster at light load.

This detector also continuously measures the wear of the top ring.


Ken

 

[greencrew]

quote:

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Originally posted by Ken2:
Very large diesels have a piston ring detector that keeps track of the rotation of the top ring. If it stops rotating an alarm sounds. It's interesting to note the different speed of rotation depending on the load...faster at light load.

This detector also continuously measures the wear of the top ring.


Ken

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Wow, I'm not sure what impressed me more, the timely 2 replys, the quality of the answers, or the idea that you can not only monitor the top ring, but measure the wear on it.

Now think about this for a second. I struggled with the concept of the rings moving. I'm not even going to attempt figuring out about the concept of monitoring it.

Thanks.

 

[cryptokid]

on most automobiles, there is a pin pressed into the piston groove so that each side of the piston ring is on either side of this pin. this prefents the rings from moving. i have personally rebuilt a subaru engine, a series 2 landrover engine, and a porsche engine, all of which has this pin preventing the pistons from moving. and some chain saws and weed wackers and lawn mowers. oh yeah, vw rabbit diesels have this pin as well. i have never actually heard of pistons without this pin, much less PROMOTION of pin movement. although i cannot see the benefit of ring movement, i would imagine the ring would never seat into the cylinder properly, but obviously this cant be the case. i guess ya learn somthing new every day, ill have to research it somtime. thanks for the new info.

yah,both my dirtbikes have the pins preventing movenent, as well as my yfz350banshee twin cylinder 4 wheeler that was stolen

 

[Shannow]

Rings need to rotate to keep the grooves clean and even out wear. Keeping the ring gaps in one location will produce a groove given enough hours.

Most mass produced engines allow this rotation.

Two strokers don't let them rotate, as they might snag a port in their travels.

Which raises a question in my mind about what the sleeve valve engines used to do, with a rotating cylinder, and a ported liner.

 

[Cressida]

quote:

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Originally posted by Shannow:
Rings need to rotate to keep the grooves clean and even out wear. Keeping the ring gaps in one location will produce a groove given enough hours.

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This appears to be in conflict with what Cryptokid said in the prior post based on his experience with a number of engines. Now I'm really at a loss for what is going on with the piston and rings

 

[MolaKule]

If the very hard and springy rings rotated, they should dig a ring groove into the soft aluminum piston and eventually the rings would "recess" into the grove, not sealing the combustion gasses.

Most rings are aligned 90 degrees in order to prvent gasses leaking into the crankcase in the form of a straight-through channel via the ring gaps. If the rings were allowed to rotate in the ring grove, there would be a certain probability they would eventually align the gaps.

Valves rotate but rings? I doubt it! What forces "cause" the rings to rotate?

[ February 16, 2003, 01:37 PM: Message edited by: MolaKule ]

 

[OneQuartLow]

Depends. Rings that aren't pinned do rotate. I wouldn't call it spinning. It isn't fast, but spiral installation, land/cylinder milling issues, or rod alignment can make them rotate slowly. Should stop for the most part after breakin when they find their place. In engines where rings pass over ports or oil grooves they need to be prevented from rotating, hence locating pins.

 

[NThomas]

i have seen a video of a cutaway of a engine, they aligned the rings, cranked the engine over at normal RPM and the rings started rotating. they moved aprox. 3/8 inch within 10 seconds
They do rotate.

 

[Shannow]

Molakule,
not exactly sure what the driver for ring rotation is. Crosshatch maybe, bore being slightly out of round, some pumping effect of the oil film.

Supposedly it's quite rapid during break-in, then a slow crawl for the balance of the engine's life.

When we did I.C. engines at Uni, proper rotation was explained as being necessary to keep the grooves clean and the rings free. I've read it in a couple of books also.

While trying to find information on the 'net, I found the following two PDF documents

See section 5 - Piston Assembly

Interesting article, and mentions rotation at the end.

 

[Shannow]

Subsequently found this link
Ring rotation and the problem of "ring spin"

 

[OneQuartLow]

quote:

---

Originally posted by Shannow:
...
While trying to find information on the 'net, I found the following two PDF documents

...

Interesting article, and mentions rotation at the end.

---

Good catch Shannow!

 

[Ken2]

The very large diesels are all two-stroke; most are uniflow with intake ports in the liner and the exhaust through a valve in the head. The piston is cast iron with a bolted-on forged steel crown.

Sulzer diesels have their SIPWA system (and I've forgotten what the initials mean). The top ring has a v-shaped groove milled into it; the groove is milled in a helical pattern, starting low on the ring face at one end and ending high on the ring face at the other side of the ring gap. A brass insert is placed into this v-groove.

A detector is mounted in the cylinder liner wall that detects when the top edge of the iron ring passes, the top edge of the brass insert, the bottom edge of the brass insert, and the bottom edge of the iron ring. If the distance from the top of the ring to the top of the brass insert is changing from stroke to stroke, the system knows that the ring is rotating ('cuz the groove is helical around the ring). The system measures the width of the v-insert and thus measures the wear; the narrower the brass, the more the ring has worn the v.

Test engines have a radioactive pellet in the liner wall to measure liner wear, but commercial engines don't get this. We still have to put a man into the liner with a mike to measure the wear (these liners are 84 cm. bore, or 93 cm, or whatever).


Ken

[ February 16, 2003, 08:56 PM: Message edited by: Ken2 ]

 

[dickwells]

Very interesting thread. I heard not too long ago that a run of small block Chevy engines (I think in Camaros) had to be recalled because of excessive oil consumption. Upon disassembly it was found that the assembler had lined the gaps up on all the rings. One would think that they would have worked their way out of alignment if they move very much.

 

[OneQuartLow]

Another cause of oil consumption is installing rings upside down. I've heard of it happening more than once on factory vehicles where the shop accused some teenager of abusing the break-in process only to find this was the cause. Or, the other half of the cause.