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Everything you wanted to know about piston rings

Inspecting the piston rings requires that the engine be removed and disassembled.
If you suspect that the ring set on your car is defective, perform a cylinder leakage test or compression test to determine the cause.
Occassionally, a piston ring will break or an engine will be overheated (which causes rings to lose their spring tension).
A broken ring can rattle during acceleration.
A cylinder ring ridge that is not removed when new rings are installed can cause a clicking sound because the square edge of the new ring hits against the rounded edge of the ring ridge. this can also force a ring land down on the second ring. the result is a stuck second compression ring or a broken ring or ring land.
A vehicle owner will usually blame piston rings for oil consumption even through oil can be lost through a variety of other conditions.
While looking for a cause of oil consumption, experts often check an engine's compression. while this procedure might locate worn or broken compression rings, it does not check the condition of the oil control rings.
Engines that suffer from too few oil changes can have plugged oil control rings.

Worn rings are found more often on a high migleage engine.
[Image: f43-01.gif]
Plugged oil control ring. Courtesy of Dana Corp., Perfect Circle Division.

Excessive leakage past the oil ring results in oil consumption and blue smoke from the exhaust.
If compression rings were working properly, the piston land between the top and second rings should be relatively clean.
The following are some of the things that can cause piston ring wear:
Leftover honing grit from a careless block cleanup.
Running the engine with a missing or damaged air cleaner or broken vacuum lines.

Using a contaminated oil fill spout or funnel.
[Image: f48-13.gif]
Compression and oil rings worn by abrasive particle. Courtesy of Caterpillar and Dana Corp., Perfect Circle Division.

When inspecting rings for wear, look for the following:

When wear is due to dirty air getting in, the top ring will show more wear and vertical abrasive lines will be visible.
The cylinder wall will show scratches in the area where the rings ride.
When ring wear is due to abrasives in the oil, the lower rings and cylinder wall will have more wear and the top ring will have less wear.
When abrasives cause wear, the bottom side of a ring will wear, leaving a lip on the outside edge.


Vacuum Test

Weak piston rings can result in low vacuum. To test for this with a vacuum gauge:

Hook up a vacuum gauge to a manifold vacuum source.
Raise the engine speed to about 2000 rpm.
Then, snap the throttle closed and watch for an increase of from 2" to 6" of vacuum above normal.
Worn rings will not increase vacuum sufficiently during deceleration.
Generally, the higher the rise, the better the condition of the rings.
End Gap

Before installing rings in a cylinder bore, check the ring end gap. The ring gap is the space where the ends of the piston ring come together after installation of the piston.

[Image: fps07-01.jpg]

To measure gap clearance, install the ring in the cylinder and square it up with a piston.
Then measure the gap with a feeler gauge. the ring must be positioned in the unworn portion of the bore, below ring travel.
The end gap is tapered, so be sure to measure at the outside edge of the ring for an accurate measurement.
To give themselves more latitude during production, manufacturers produce rings that have 0.005-0.010" more gap clearance than the minimum specification.
If any gap is too narrow, the gap can be increased by a file or ring gap cutter. If a file is used, cut from the outside of the ring toward the center.
Correct all rings requiring wider gaps.
If the ring gap is too wide, it is possible the gap was checked with the ring in a slightly worn area of the cylinder bore.
The ring gap should be at least 0.003" to 0.004" for each inch of cylinder bore diameter unless otherwise specified in the repair manual.
Following is a general specification chart that may be used if manufacturer's specifications are not available.

The ring end gap can be filed to fit if it is not wide enough.
One manufacturer states that maximum gap clearance is not as critical and can actually be as much as 0.030" more than the minimum specifications without causing blow-by.
The important thing about ring gap is the minimum specification. Too small an end gap can cause the rings to lock up in the bore as they heat and expand. Ring end gap lockup results in scuffing and ring failure. The ends of the ring will appear polished if this happens.
An increase of 0.002" in the bore size would increase the gap by about 0.006". Installing standard rings in a 0.030" oversized cylinder bore would result in an end gap increase of approximately 0.090".
The gap will change by about 0.030" for each 0.010 error in size.
A common error is to want to install oversized rings in badly worn cylinders. An oversized ring might fit into the top of a tapered cylinder. Because of the tapered cylinder wear, the gap on an oversized ring would lock up as the piston moved down the cylinder wall.
The figure below shows rings that were too small for the cylinders they were run in. Notice the dark area (carbon deposits) near the gap.

[Image: f48-14.gif]
Rings that are too small for the cylinder will have the appearance of carbon deposits near the gap. Courtesy of Dana Corp., Perfect Circle Division.


Piston rings are replaced whenever an engine is disassembled. Also, if a cylinder head is removed for repairs and the oild pan is readily accessible, the customer might opt for the installation of new piston rings.

There are three piston rings on a piston.

[Image: f15-24.gif]
Piston and rings. Courtesy of General Motors Corporation, Service Technology Group.

The top two rings are compression rings. They seal between the piston ring grooves and the cylinder wall, keeping combustion pressure from entering the crankcase (blow-by).

[Image: f15-27.gif]

Oil is scraped off the cylinder wall by the oil ring and returned to the crankcase through holes in the piston.
Removing Piston Rings

Disassemble the engine and remove the pistons.
Compression rings are removed with a ring expander.

[Image: f48-03.jpg]

Using a shop rag to remove or install a compression ring.
Oil rings are easily removed by rolling off the rails and removing the expander spacer.
Clean the piston ring groove and check the ring groove wear/side clearance.
Installing Rings on Pistons

Be sure the rings used are the proper ones for the piston. Pistons designed for use with low-tension rings have ring grooves that are shallower than standard ones.
Use a ring to double-check for correct groove depth. Roll the ring around the entire groove to ensure that the ring does not bind up on the edges of the ring land.
Check the end gap prior to installing the rings on the pistons. oil rings are installed first. then, the second compression ring is installed. finally, the top ring is installed.
Oil Ring Installation

Most automobiles use three-piece oil control rings, consisting of an expander spacer in the center with two outside rails. Install them as shown in the figure below.

[Image: f48-17.gif]
Installing the oil ring rail. Courtesy of Federal-Mogal Corporation.

Install the expander spacer, being careful not to overlap its ends.
The ends are usually painted different colors to make it obvious to the installer if they are accidentally overlapped.
Some expanders are filled with a Teflon button on their ends to prevent improper assembly.
In the absence of a recommendation, position the expander gap above one end of the wrist pin.
Next, install the rails. Installing the top rail first is easiest.
While holding your finger over the butted ends of the expander, install the top rail.
Position its gap above the skirt on one side of the expander spacer gap.
Install the lower rail with its gap placed above the skirt on the opposite side of the expander gap.

[Image: f48-18.gif]

Oil ring gap positions. Courtesy of Federal-Mogal Corporation
Compression Ring Installation

Piston rings are often tapered or have chamfers or reliefs to cause them to twist.
These piston rings must be installed with their identification marks facing up.

[Image: f48-19.gif]
Ring identification marks face up. Courtesy of General Motors Corporation, Service Technoloogy Group.

Installing them upside down will result in severe oil consumption. In fact, one compression ring installed upside down can double an engine's oil consumption. The second compression ring actually controls more oil than compression.
Use a ring expander to install the compression rings.
If a ring expander is not available, a shop rag can be used as shown above.
It is important not to "spiral" or roll the rings on; they can become distorted to resemble a lock washer.

[Image: f48-20.gif]
Improper installation can ruin a piston ring.

Overexpanding plain cast iron rings during installation can very easily result in a broken ring.
Compression Ring Gap Position

The gaps are placed at different locations around the piston. Manufacturers specify different gap positions in their service manuals.

According to information published by engineers in the Perfect Circle Division of Dana Corporation, the reason for the practice of staggering ring end gaps is to guard against scuffing when an engine is started for the first time.

As the engine operates, rings will rotate from the position they were first installed in.

End gap position is not a cause of oil consumption.
There are many differing opinions on ring gap placement. The most prudent policy is to follow recommendations of the vehicle manufacturer, when available.
The positions shown below are popular in the aftermarket.

[Image: f48-21.gif]

Chart showing popular ring gap placement.

Taken from,GM,federal mogul,cat and dana corp
Good stuff. Good find Rob. Thumbup
Ain't no squad like the EJ8 SQUAD..
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nice to know information will look into it when i take my head off thanks man Smile
I live my life a quarter pounder at a time nothing else matters.
at the end of the day its my car i see it everyday i drive it every day so feel free to express your opinion but dont hate on me for expressing my style Smile
very nice find rob! i have been wanting to read up more on pistons and rings, when i have more time i will be reading this
Nice post very good info.
97 Civic Hatch (EK9 Clone)
Good info!
Well done. Bookmarked.
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Actually, way more info than I wanted to know about rings. Lol. Very good informative read here. Thanks!
This tutorial will help people for the rest of time thankyou so much publisher!
Its really wonderful. Thanks a lot for sharing.

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