Setting Piston Rings in Cylinders

[Bruce Lancaster]

The aligned gaps would have to provide enough flow to dump almost all the cylinder's energy, seems to me...no way.
I happened upon a manual for a 2000 Toyota V6 Camry this morning (had car for 15 years, have only glanced under hood for such things as refilling windshield washer. Can't tell you much of anything about the motor.)
Interestingly, there was a diagram of how to align rings at installation, AND all the gaps were to be in a 180 degree arc on one side of piston! So Toyota is still interested in these issues...

(looked at the Toyota ring placement charts again...the arc where all the gaps are to be put is the front of the cylinder in traditional terms, the end opposite transmission attachment... the engine is of course sideways to confuse me. That would mean it is spanning between the thrust and non-thrust sides, if that is a factor. Fortunately, I don't own enough metric sockets to tear in there and see where they are now!)

[51 MERC-CT]

Originally Posted by Bruce Lancaster

The aligned gaps would have to provide enough flow to dump almost all the cylinder's energy, seems to me...no way.
I happened upon a manual for a 2000 Toyota V6 Camry this morning (had car for 15 years, have only glanced under hood for such things as refilling windshield washer. Can't tell you much of anything about the motor.)
Interestingly, there was a diagram of how to align rings at installation, AND all the gaps were to be in a 180 degree arc on one side of piston! So Toyota is still interested in these issues...

Interesting, so I decided to check the shop manual on my '14 Transit Connect.
Seems that even Ford is concerned about ring gap location.

[amodel25]

Not taking sides on this one, just relaying a story from my youth.......1968, High School Vocational Auto Mechanics Class. We had a sales Engineer from Perfect Circle Piston Rings visit our class and give a talk on pistons and rings. When asked about ring gap alignment, he said "Install the rings with the gaps set any way you want to, drive the car around for an hour, pull the head(s) and if the gaps are in the same place as they started, I'll buy everybody in this class a steak dinner."

[JAKEFORD]

There seems to be convincing arguments as to piston ring rotation. A few questions may be in order: (Assuming a cylinder bore that is in tolerance and not worn to excess)

What effect does the cross hatch pattern have on rotation?

After installation and start up, if the rings rotate do they settle in a final position and spend the rest of their life there?

What effect does ring pressure on the cylinder play? Do skinny rings tend to rotate more?

What effect does the lubricant play? If the oil rings are working there shouldn't be a lot of oil or else the engine will burn a lot. But the oil trapped in the rings lands could be a factor.

Thanks

[mike in tucson]

Dear Dr. Flathead:
My manual says to hone the engine using a crosshatch pattern oriented about 45 degrees to the axis of the cylinder. My question: should the hatch pattern progress to the left or to the right going down the cylinder? I can run my hone either clockwise or counterclockwise. Also, if I am in the Southern hemisphere, should I do the honing in the opposite direction?

[scooder]

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Jake,
I don't know the answers to your questions, I know a lot of folk don't give a shit why the rings move. They do move, that's a fact. And that's good enough for most. But I do like some ponder thinking every now and again, so I'd like to know the answers too.
I have some pistons here that came out of an 8BA in a pickup, it "smoked a bit" apparently. There are places around the piston where the rings had broke and worked their way around and on top of other sections of ring! Yup the ring land had been worn to a point from age and ring rotation I guess, that allowed two thicknesses of ring, one on top of the other!
Martin.
"it smoked a bit"

[cmbrucew]

Just how much ring gap are we talking here, My book calls for .0015 to .003 .
Bruce

[rotorwrench]

On the aircraft engines, we do a compression test every 100-hours of flight time utilizing a differential pressure leak down test rig. If we find one that is excessively low and it is pressuring up the crank case, we run the engine on the ground for a while and then recheck it. If the rings are lined up, they will usually rotate away from alignment after a 5-minutes of run time. If it is still low then we pull power with it in flight for a trip around the patch before we consider taking a cylinder off for repairs. It's hard to explain to a customer that we pulled a cylinder and found nothing wrong except for aligned rig gaps. This will generally take place several times within the overhaul life of the engine. It's not as uncommon as some folks might think.

Ring gaps should be far enough apart that there can be no end to end contact when the engine is hot. It they make contact, the ring will break. Every manufacturer has different specs for ring gaps.

[51 MERC-CT]

Originally Posted by cmbrucew

Just how much ring gap are we talking here, My book calls for .0015 to .003 .
Bruce

Better re-check the specs. Doesn't sound like end gap but like ring to land clearance.

[Ronnie]

Originally Posted by cmbrucew

Just how much ring gap are we talking here, My book calls for .0015 to .003 .
Bruce

You should re read that book I believe you will find that reference is not about ring end gaps all,but perhaps ring clearance in the ring lands.
Also remember that ring end gaps are determined by bore sizes at the factory with light gauges. All the rings leave the factory having met the ring gauge specs. The rub begins when the end user begins to hone the engine for a re ring and exceeds the determined bore size which changes the end gap it is as simple as that.An example would be a ring set in standard at 4" not 4.005 not 4.009 but at 4.000. If you had a bore that was serviceable with .005" wear the ring gap on that standard ring when measured in the 4.005" finished bore size would open up by the formula of "pie" about 3.14" for every .001" increase to be added to the advertised clearance,for every .001" increase on diameter,thus the reading would be that much larger but not enough to change the performance in a street engine. Another consideration is the clearances are minimums not maximums. (every .001" increase in bore produces another 3.014" in end gap)
Many papers have been written on this and there are engines today that are built with gaps much larger than those specs that are adhered to.
The specs originally come from SAE and not necessarily the ring mfg's

R

[51 MERC-CT]

Originally Posted by Ronnie

(every .001" increase in bore produces another 3.014" in end gap)


R

Wow! that's a big gap

[Ronnie]

Originally Posted by 51 MERC-CT

Wow! that's a big gap

Fat fingers"LOL" .00314"

R

[Capt Kirk]

LOL...I have no idea what my ring gaps are or even if they're aligned. My engine runs well and that's what counts. There probably hasn't been an engine pulled and rebuilt because the ring gaps were aligned. I'm a pilot and know a bit about the rings in a new built engine not seating resulting in burning some oil. Boss said to run it hot to get them seated...didn't work totally in that case but it wasn't because of where the ring gaps were.

[JAKEFORD]

Has anyone had any experience with the Gapless ring?

It overlaps at the former gap and is said to improve HP, reduce blow-by and keep alcohol out of the crankcase in race engines.

Rotation is probably not an issue in either the north or south hemisphere with this ring.

[flatheadmurre]

Here you have 3 more or less engineered gaps.
The cost of the most overengineered ring must be huge....

[Pete]

Originally Posted by JAKEFORD

Has anyone had any experience with the Gapless ring?

It overlaps at the former gap and is said to improve HP, reduce blow-by and keep alcohol out of the crankcase in race engines.

Rotation is probably not an issue in either the north or south hemisphere with this ring.

I have used Totalseal gapless rings in several engines.
They work fine. They have about 2% leakdown as opposed to 5 or 6 with conventional rings on a new installation.

[Tom Walker]

I believe a rule of thumb for ring gap is 0.004" per inch of bore for the top ring, and 0.003" per bore inch for the second ring.

[SofaKing]

[QUOTE=JAKEFORD;1165727]Has anyone had any experience with the Gapless ring?

Yes. I did not notice a seat of the pants difference between them and cast rings. At next teardown they had practically no tension so I went back to cast rings.

[JWL]

If you read my book you will see the gapless top ring can be a good choice and the gapless second ring can cost power. A long explanation is in the book.

[Ronnie]

Originally Posted by Tom Walker

I believe a rule of thumb for ring gap is 0.004" per inch of bore for the top ring, and 0.003" per bore inch for the second ring.

Take into consideration that those figures are minimum gaps for a stock street engine..

R