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Piston rings


Terminator20's Avatar
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11-16-03, 12:31 AM   #1  
Piston rings

I am trying to learn more about piston rings. If you did not have piston rings, would the engine run? What are they for? The last question I have about piston rings is, how would the piston rings cause oil burning spacifically?

 
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mower17's Avatar
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11-16-03, 05:54 AM   #2  
O.K. There are two types of rings, compression rings and oil control rings. Depending on what engine you have, there will be a certain amount of each rings on each piston.(chainsaws and trimmers have one or two compression rings but no oil control rings, briggs angines have at least two comression rings and at least one oil control ring, diesel engines can have up to four comression and four oil control rings) The purpose of the rings is to seal off the compression so it stays in the cylinder above the piston. An engine will never run, if fact it will never start without rings, that goes for every engine. The compression rings seal off the compression so it stays above the piston while the oil control rings act as a scraper when the piston goes down on every stroke since oil will get thrown on the cylinder walls during opperation and it can't all stay there, however, a thin film of oil does have to be left so that the compression rings will get lubrication. If these oil control rings get worn too much then they don't do their job as well and oil gets to the top of the piston where it will be burned and cause that blue smoke. Rings have to be replaced after a long time of using the engine since they will wear out. It is also just as important to have the cylinder walls just as flawless as the rings since it is one of the most important things that has to work for the engine to opperate. If the cylinder walls have a scratch in them then that cylinder will not have good compression and that is a very bad thing. Some rings even have to be placed in certain grooves even though they all look the same, there is even a top to them that has to face up, it is that important to propper engine opperation. Even if the gap between the ends of each ring(this is known as end-gap) are one or two thousanths of an inch more than they should be, then the rings are no good. Likewise, if the gap between the side of each ring and the inside of each ring groove(this is known as side clearance) is one thousanths of an inch more than it should be, then either the rings are no good or the piston is no good. Even how the gaps at the ends of each ring are placed on the piston will make the differance between the engine have lots of power and the engine having little power, the propper way to to put the gaps is 180 degrees apart from each other so very little compression is lost. A good mechanic will check these, though some mechanics don't. Compression is the most important factor to a diesel engine. I remember one time not long after the summer I was overhauling a diesel engine on a tractor and I thought, "why check end-gap and side clearance"? Well that tractor never started and I got the wonderful oppertunity to take everything back off that I JUST put on and do what I didn't do the first time. Lesson learned VERY WELL that doing a job half way is a very big mistake. That's why mechanics go to great lenghts to make sure to get these rings right cause if the cylinder is leaking just a little after an overhaul, then they get to tear everything back down and find the problem. That's why using ether is a BIG mistake, it will break the top compression ring and the only way to replace it is to tear into the engine which costs the customer money and chances are, if it runs then that's good enough for them, so once the damage is done from the ether, to be able to start it on the next time, they have to use more ether. This process is known as an engine being spoiled to ether. Even though the engine will not start right up, a good mechanic will hardly use much if not any ether even though he might have to struggle with the engine a little longer. Also, getting the rings to seal propperly with the sides of the cylinder is known as seating the rings, which is done by running the engine for a while with a load on it. As you can see, rings are very important to an engine since breaking a ring is a very bad thing and that not being able to get the rings to seal can make the difference between an engine running like brand new or an engine not running at all. Hope this helps!!!!!!!!


Last edited by mower17; 11-16-03 at 06:24 AM.
 
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11-16-03, 08:42 PM   #3  
Good explanation mower 17!

Also, let me add a couple details. When the rings get replaced, honing the cylinder is required, unless the cylinder is aluminum. Proper honing is vital to ring seating/engine break-in. There must be a cross-hatch pattern of around 30 degrees uniformly along the cylinder walls. This does two things...it helps wear the parts together to seat in, and the fine scratches provide lubrication for the rings. A very small amount of oil gets in these scratches and helps lubricate the parts. Also, if there is a ridge at the top of the cylinder, it should be cut out with a ridge reamer. If this is not done, the top ring can and often does break. Especially if a new piston and/or rod is installed. A broken ring can RUIN an engine in less than one second.


"Who is John Galt?" - Ayn Rand (Atlas Shrugged)

God bless!

 
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11-16-03, 09:35 PM   #4  
After learning all this great information I have decided to not replace the rings myself, and let a mechanic do it. As much as I hate to do that. This will not be done anytime soon anyway. This will be done next year hopefully. If I can not get it done next year cause of financial issues than what I will do is keep running it while I save up a little money each month untill I can get the rings replaced. Basically the problem is that its burning blue smoke. Not a ton of blue smoke, just ever so slightly to where you have to really look at the muffler and you will see it slightly burning oil. You can barely see it. But you sure can smell it! I have brought this up to Cheese in the past and he told me the causes for blue smoke. I have rulled out many causes because, even though the carb is 15 years old. I have replaced parts inside it and adjusted it to the best it could be adjusted, and its still burning oil. I even got the right oil in it. SAE 30. That is what all these engines take. Basically because of the oil burning it is fouling spark plug. Once I clean it, it fires right up. After some use, and you take the plug off and look at it you can understand why it does not want to fire up. Because its filled with burnt oil AKA chared! Sence I know this engine is 15 years old, its got to be the rings. I don't think its the fly wheel key because I have never really hit anything hard with it. But remember what I said before? I got this mower free from this guy who had it all that time before, so, for all I know it could be parshaly sheard. Basically it runs well when the sparkplug is clean. But as soon as it gets a full consontration of oil burning, no more fire. Now because I replaced the oil this month, I will not be able to test the new oil untill next year. Also next year is when I will pop the shroud off and take a look at the flywheel key. Anymore information you can give on this subject would be greatly appreciated...Mower17...Cheese

 
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11-16-03, 10:00 PM   #5  
A sheared flywheel key will make itself obvious. The engine won't run well. It is not likely that a sheared key will cause enough oil consumption to cause smoke. It could cause an engine to use more oil than it should, but not so much that it smokes. Same thing with a carb problem...won't make it smoke (blue smoke anyway).

Replacing rings sounds like a fine science by reading the previous posts. Don't let that scare you away from doing this yourself, if that's what you want to do. It is not hard at all, and if you let a mechanic do it, he may not do any of the checks that should be done. Many small engine mechanics just tear the engine down and stick a new set of rings in and button it back up. Yeah...that might work more times than not, but to do it right, and have confidence in the work you did, you have to do the things we mentioned. You can do this in one afternoon, and the tools needed can be rented for free at autozone.

You will need:

Ring compressor
Ridge reamer
Cylinder hone...unless you have an aluminum cylinder
3/8" drive torque wrench
feeler gague set
basic hand tools
pan gasket, head gasket, bottom crankcase seal


"Who is John Galt?" - Ayn Rand (Atlas Shrugged)

God bless!

 
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