Blue smoke out of the tail pipe, low compression, excessive blow-by, excessive motor oil consumption, loss of power.
A more detailed answer
If all your piston rings are badly worn you'll have blue/black smoke coming from the exhaust every time you accelerate and your engine oil dipstick will show the oil being used up much faster than usual, like you will have to top-up with a pint of engine oil every 300-500 miles. If only one or two pistons have worn-out piston rings the symptoms would not be so bad.
It all depends on how well the engine has been driven and maintained. On a modern engine, say less than 15 years old, if the oil was changed regularly and the engine was never thrashed (over-revved) then it is unlikely you'll get worn piston rings until the engine has done 150 thousand miles, or much more if it's a diesel.
Note
On modern engines with overhead camshafts, if the valve-seals are worn you'd also get blue/black smoke coming from the exhaust every time you accelerate and would be burning up engine oil fast. Even if the engine was driven well, and its oil was changed regularly according to the recommended service intervals, its valve-seals are still liable to wear out faster than its piston rings. How long the valve-seals last will depend most of all on the quality of the materials used by the engine manufacturer and, to a lesser extent, on the engine size: on some makes of engine the valve seals could normally need replacing every 100 thousand miles, on others they could last 300 thousand miles or more.
The piston rings create a seal between the piston and the cylinder wall.
It is a spring metal sleeve that goes over a piston to compress the rings so that the piston can be install in the motor. It tightens down on the piston, forcing the rings into the grooves in the piston then you tap it into the cylinder.
Could do as the fuel/air mix although would be the right consistency it would be diluted by being able to transport down the cylinder block. therefore you wouldn't get as big a bang!
With a piston ring compressor.
You are talking about an engine overhaul. It could run thousands, parts and labor, depends on the year, make and engine.
bad valve seals, bad piston rings bad valve seals, bad piston rings
Worn piston rings, bad valve seals,
bad piston rings or a bad cylinder all together look up a rebuilder bad piston rings or a bad cylinder all together look up a rebuilder Worn piston rings and or bad valve seals. Could be from high mileage or poor maintenance either way there is no cheap fix.
If you're getting gasoline in the oil, then you have bad piston rings that are allowing gases into the crankcase. You can find which piston(s) have bad rings by doing a compression test; a cylinder with bad rings will have lower compression.
smoke loss of power
loss of power
you don't fix piston rings. if you have bad rings you have to pull the piston and replace them. on most vehicles you have to pull the engine, then you take off the heads and oil pan. unbolt the caps from the bottom of the rod and push it out the top.
Bad piston rings. Get new engine.
bad piston rings
You might have bad piston rings, main cause of that because once you wear your rings out your gas is then able to seep past your piston rings into your oil and into your pan.
no, you have bad piston rings
The piston rings create a seal between the piston and the cylinder wall.