What do worn piston rings look like?

[Stephen Tashiro]

What do piston rings look like when they are worn enough to let too much oil leak by, but not worn enough to disintegrate? If I looked down the side of a piston (say, using a borescope) could I see that the rings were bad?

The way I think of piston ring, as the rim wears off, there is less and less pressure forcing the ring against the sides of the cylinder. When the rings start leaking oil, can you actually see some daylight between the edge of the ring and the wall of the cylinder? Or does the leakage start a long time before there is any visual evidence?

[Shawn Pixley]

If you could see a gap, I doubt that the engine would run at all. The ring sits in a gallery in the piston. The gap in the ring will get larger with ring wear but you wouldn't see a gap around the cylinder. Long before that you would get so much piston slap your engine would be ruined. Your engine would sound like it is about ready to fly apart.

Testing rings is done using a compression tester.

[Brett Robson]

The rings you could see are the compression rings. The oil control rings are below the compression rings and wouldn't be visible without pulling the pistons.

Here's a picture, just because I happen to have some pistons lying about! The oil control rings are just above the wrist pin.

[Mike Henderson]

With today's oils, if you maintain your car as prescribed, it's unlikely you'll have significant ring and bore wear. My indication has always been to look at the top of the cylinder bore and see if there's a "lip" at the top - at the location where the the top ring of the piston reaches. If so, your rings may need to be changed, but you may also need to bore out the cylinders. But again, I say that with modern oils, worn out rings are unusual.

I'm old enough to remember when the bearings on the crankshaft would wear and you'd have to change the inserts (a "bottom end" job). That's unheard of now. Next, it was ring and cylinder wear - take out the pistons, hone or bore out the cylinders, and replace the rings and maybe the pistons (a "top end" job). Essentially unheard of now. Lastly, it was the valve guides that wore and oil would seep past the shaft of the intake valve (a valve job was needed about every 50K miles). Today, highly unusual in a well maintained engine.

Modern engines that are well maintained just go on and on.

Mike

[Rick Potter]

A carpenter friend of mine has a 10 year old Chevy pickup. It has over 300,000 miles on it, and the rings are still the originals. The accessories are going bad, at a regular rate, Alternators, starters, fuel pumps, etc, but the basic engine is sound. He maintains it regularly.

We used to hear a lot about how long Rolls Royce car lasted. I am sure they are really well built, but suspect regular mainenance has a lot to do with it. See above for a test case result.

Back to the question of what worn rings look like using a bore scope. Just like good ones, unless a top one is broken. The best way to check is a compression test and a leakdown test, neither of which is visual.

Rick Potter

[Myk Rian]

The way I think of piston ring, as the rim wears off, there is less and less pressure forcing the ring against the sides of the cylinder. When the rings start leaking oil, can you actually see some daylight between the edge of the ring and the wall of the cylinder? Or does the leakage start a long time before there is any visual evidence?

You do a compression test with a pressure gauge.

[John Coloccia]

You can actually still get to the pistons? I'm surprised engines aren't just welded shut these days.

[Jeff Monson]

The way I think of piston ring, as the rim wears off, there is less and less pressure forcing the ring against the sides of the cylinder. When the rings start leaking oil, can you actually see some daylight between the edge of the ring and the wall of the cylinder? Or does the leakage start a long time before there is any visual evidence?

If you look at the picture that Brett provided, the top 2 rings are your compression rings (responsible for creating compression), the bottom set of rings are the oil control rings (2 rings with a spacer inbetween) these are responsible for oil control. If you have an oil consumption issue, its most likely the oil control rings are stuck, they get full of carbon so they can no longer "float" around the piston. That results in oil getting to the compression rings, then the oil gets burnt instead of getting wiped down the cylinder and back to the oil pan. If you are having oil consumption issues, this can also be caused by the valve train (worn valve guides, or bad valve seals), or possibly a PCV system that is not working correctly either.

[Kevin Bourque]

You can do a simple compression test to determine if the rings are bad, or you can have a mechanic hook the car up to a diagnostic computer. Using a scope won't really tell you much at all.

[Joe Angrisani]

....Testing rings is done using a compression tester.

You do a compression test with a pressure gauge.

You can do a simple compression test to determine if the rings are bad.....

No no no. Please return to your shadetree and stop giving mechanical opinions for the sake of posting something.

Read Jeff's response. The compression rings have nothing to do with "letting too much oil leak by", as the OP asked. The oil rings have nothing to do with compression, as Myk and Kevin proclaim. Besides, I don't know a single mechanic who would waste time with a compression test. In all my years wrenching, I've NEVER done a compression test. We only did "leakdown tests", which not only show a problem, but shows whether the loss of compression is due to the rings, the intake valves, the exhaust valves, or the head gasket.

[Joe Angrisani]

What do piston rings look like when they are worn enough to let too much oil leak by, but not worn enough to disintegrate? If I looked down the side of a piston (say, using a borescope) could I see that the rings were bad?

The way I think of piston ring, as the rim wears off, there is less and less pressure forcing the ring against the sides of the cylinder. When the rings start leaking oil, can you actually see some daylight between the edge of the ring and the wall of the cylinder? Or does the leakage start a long time before there is any visual evidence?

Stephen....

What engine are we talking about? What are the symptoms? How fast is it consuming oil? Big stinky cloud on startup? Cloud only on hard acceleration? No cloud - oil just disappears from dipstick? Any oil on driveway? How's it run? What did the plugs look like when you pulled them?

Give us any and all observations.

[Stephen Tashiro]

Stephen....

What engine are we talking about? What are the symptoms? How fast is it consuming oil? Big stinky cloud on startup? Cloud only on hard acceleration? No cloud - oil just disappears from dipstick? Any oil on driveway? How's it run? What did the plugs look like when you pulled them?

Give us any and all observations.

Let me emphasize that I'm interested in the general question of whether piston rings can be inspected visually, not in solving one particular engine problem.

An engine that is handy at the moment is a Toyota 4AFE on a friend's 1990 Corolla with about 200,000 miles on it. He hasn't changed the oil in a long time. We drained the oil and I think it would be interesting to look in the engine with a borescope. I want to look through the oil pan drain hole and check that the screen on the oil pump isn't clogged. I think it would be interesting to look at the other parts of the engine from below and (from the spark plug holes) above. The engine doesn't emit a cloud of smoke. The plugs have some dark carbon deposits on them. I'll know more after I look with the scope.

I have done both compression tests and leak down tests on various engines. (My friends engine has compression of about 150 psi in all cylinders, which is adequate. The spec is 191 psi for a new 4AFE and 142 psi minimum.) I'm simply curious about what one can tell from a visual inspection.

I think about things like putting a little oil in the sparkplug hole (as in a "wet" compression test), applying compressed air to the spark plug hole and looking at the sides of the cylinder from below with the scope to see how much oil blows by the rings. However, I'd have to do the same test on an engine known to be good to make sense such results.

[Jeff Monson]

Pretty tough to get an answer with a scope, or with a piston still in the block, if that is the question you are looking at getting answered. I've looked at plenty of pistons still in a block and all looks ok, when they are removed the answer is usually revealed. In the case of your friends Toyota, lack of oil changes, I'd put my money on stuck oil rings, I have seen plenty of them in my day. Its really an easy fix, I'd also bet there is very little to no cylinder wear.

[Joe Angrisani]

.....I'm interested in the general question of whether piston rings can be inspected visually....

No, they can't. Neither compression rings or oil rings.

[Myk Rian]

Let me emphasize that I'm interested in the general question of whether piston rings can be inspected visually, not in solving one particular engine problem.

Only if you remove the pistons from the engine.