The piston is an integral part of an engine of the dirt bike. That’s why we are going to discuss the functionality of the piston ring the dirt bike and understand how do piston rings work?
A piston ring is a type of ring that fits into the OD groove of a piston. These are made to maintain the combustion pressure and cylinder pressure of the IC engines. There are three types of piston rings Top Compression ring, Secondary compression ring, and oil ring.
How do piston rings work?
Piston rings have three main functions. The three major roles that the piston rings are going to play is that they’re going to keep whatever is in this chamber—in your combustion chamber out of your crankcase, they’re going to keep whatever is in your crankcase out of your combustion chamber, where you have oil.
Then they’re also going to help facilitate heat transfer between your piston and the cylinder wall.
So Pistons are in contact with the piston rings, those are in touch with the cylinder walls, and that’s how heat is going to be transferring from pistons to your cylinders.
On the piston, there are three rings. So the top ring is the compression ring, and that’s helping to seal that combustion chamber you get good compression and so that you don’t get any of that air and fuel mixture down into your crankcase which is known as blowby.
And so the second ring there is a mixture of both the top ring and the last ring and that last ring is an oil scraper ring and thus it’s helping to keep the oil out from the combustion chamber that’s in your crankcase that’s lubricating those cylinder walls.
Also, there are little holes right underneath that oil ring. And so what those holes are for is they’re going to pass that oil through the piston back into the crankcase, so it’ll scrape it down on the walls and that fuel to get scraped on the walls will pass through the holes and fall back into your crankcase.
So as we mentioned, the middle ring is going to be helping to scrape oil on the walls, and it’s also going to be contributing to seal the chamber for compression.
So how do piston rings allow for blow by well and this is a bit of an exaggerated look into it? So on the exhaust stroke, when the piston is moving up, you can see the piston rings are going to be pressed down, and there’s a gap behind them between them and the piston itself.
So your exhaust fumes and gases can get behind that gap and then on your intake stroke which occurs after your exhaust stroke.
The pistons are then going to move up and so as they move up and hit the top of the piston, those gases can now pass underneath them and travel down and eventually making their way into the crankcase.
So that’s blowby, where you’re getting gases from your combustion chamber and getting them into your crankcase.
The piston gap is going to be quite a bit smaller. It’s going to be very small as far as the gap there, but it exists nonetheless.
That gap exists so that this ring acts as a spring, so it expands out, and as the metals within the engine expand and contract based on different temperatures, you can make sure that you
have good compression, because the rings will expand out and meet up with the cylinder walls so that you have a beautiful sealed chamber for combustion.
Nonetheless, these gaps will allow for some of the air and fuel mixture and your combustion gases to pass through and get down within your crankcase.
So what happens if your piston rings have worn out? Well, you’re going to have two problems occur because of that. First of all, you’re gonna have low compression, and as a result of low compression, the amount of power you make and the efficiency of the engine is going to go down, and you’re also going to be burning oil because some of that oil isn’t going to be scraped off and it’s going to be making it into your combustion chamber.
So, less power and burning oil. So it’s not a significant problem to have. And, unfortunately, going in and replacing these is going to be expensive, because you pretty much have to tear down the whole engine.
The dirt bike has a different kind of issues like sputtering, backfiring, smoking etc. but dealing with these issues needs some basic knowledge which we have discussed in this blog in detail.
Symptoms of bad piston rings 2 strokes:
The bottom of the piston ring may have a dark coating on it, and also on the ring, there will be a little bit of coating on the top, but mostly on the bottom, the coating fades. It’ll curve a little bit more than it should be.
So if you are planning to change a piston or a piston ring, make sure you cover up the underside of the piston, so nothing falls into the bottom end of the motor especially the little clips. A small clip that holds the piston pin in there when you try and get those out they very quickly fall into the bottom end of the motor and then you’ve got serious trouble.
Piston ring failure:
Bent Reins
The most common problem is bent reins; this is caused by improper installation, the bent ring results in leakage of blowby and oil.
Lock washer
A lock washer occurs when ring points are bent out of alignment usually by improper handling and also results in a high blowby and oil consumption.
Steel shot embedment
Steel shot in Penman is the result of a piston run in an engine in which the heads and intake manifold has been cleaned with steel shot that was not entirely removed resulting in engine failure.
Glass beads
This can cause excessive blowby or oil control and abrasive wear to all engine parts with the resulting reduction in engine life and possibly complete engine failure.
Steel shot
Damage also happens when the engine has been cleaned with steel shot which was not entirely removed.
Pockmarking on ring sights is from the shot caught between rings and piston groove.
Overheat
Overheat can be detrimental to the piston ring’s performance. The piston shows oil cake below the ring belt, indicating excessive cylinder temperature. Any old ring which was removed from an engine that was overheated, you can notice the bluish cast lack free cap loss of ring tension and misalignment of ring points.
Excessive ring rotation
Excessive ring rotation occurs when the compression rings and oil rings exhibit high side wear with a wear ridge near the OD. Excessive ring rotation can be caused by misaligned connecting rods, piston grooves not perpendicular to piston skirt, excessive crankshaft play and excessive engine vibration.
Abrasive wear
Abrasive wear is caused by several factors some of the reasons include leaks in the air induction system, cracked or broken vacuum lines, leaking intake manifold, cylinders and engine parts not properly cleaned, abrasives in engine oil.
Bore finish
Proper bore finish is critical to piston ring performance. Hastings ring materials are compatible with industry-standard honing practices for cast-iron cylinder bores.
Oversized bore
The standard rings that have been run in an oversized bore. You can notice the irregular wear pattern due to a lack of sealing unacceptable blow by in oil control is the result.
Groove depth
Groove depth issues occur when piston grooves are too shallow, or piston rings are too serious severe engine damage will result.
Conclusion
Today in this post we have discussed the functioning of piston rings and also understood how do piston ring work? We have talked from the different aspect of it’s working process and briefly, we have also got some knowledge about the symptoms of a bad Piston ring.
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