<font color="#000000">Just wanted to post a test explaining the differences between the 2 test and give some examples.........</font></p>
<font color="#ff0033">COMPRESSION TEST</font>......<font color="#000000">What a compression test does is tells you how much pressure that piston/rings can make moving from the bottom of the cylinder to the top. The problem with a compression test is that it is not a real accurate way to determine the health of a engine as it usually has to have a very serious issue to show up on a compression test. I have a insert out of a manual that states if a engine has equal compression and is hard to start or runs poorly, to check for mechanical issues. So even OMC (Johnson/Evinrude) understands this and puts this in their service manuals. All engines work off the same principles. I have dealt with several engines that have passed a compression test and failed a leakage test. </font></p>
<font color="#000000">I mainly use a compression testto help determine what octane fuel that a engine requires. The higher the compression, the more heat is produced in the combustion chamber. This can cause the temperature in the combustion chamber to ignite the fuel instead of the spark plug (detonation). Causing engine damage. The higher the octane, the slower the fuel burns at the same compression ratio. So to get the most out of the fuel, you need to use the correct octane for your compressionas too high of octane will cause a 2 stroke to actually loose power. More on this later!</font></p>
<font color="#ff3300">LEAKAGE TEST</font><font color="#000000">..... First you must understand what happens in a cylinder. The piston begins moving to the top of the cylindercompressing the air/fuel charge making it more flammable.Just before the piston reaches thevery top of the cylinder, spark will occur. (thisknow as timing for example 23* Before Top Dead Center)Just as the piston reaches the top and starts on it's way back down the air/fuelthat has already startedto burn will finish burning creatinga large amount of pressure pushing on the piston thus rotating the crankshaft, drive shaft, and then the prop.So what a leakage test does is check the seal of the piston rings and gasket. Remember whencombustion is happening, there is a large amount of pressure pushing on the piston. If you have a poor seal, then some of this pressure will go elsewhere and the engine will have a power loss. This leakage is also known as blow by. Now that you understand what is going on you can see if you run 93 octane (slower burning) in a engine that needs 87 octane (faster burning) it will mess up the combustion process and cause a power loss. </font></p>
<font color="#000000">What a leakage test does, is induces air into the cylinder as the engine is being held from moving and this tests the seal of the rings and head gasket. What I do is remove all the spark plugs and using ascrewdriver I will rotate the piston to the top and then down 1/2" to 3/4" past theTDC (top dead center)and mark my screwdriver with tapeso all are tested at the same height. I do this as a carbon ring will form at the top of the cylinder and give you a false reading. I will include Ditchdoc666's engine as a prime example of this. I willthen hold the engine with either a pair of vice grips on the flywheel pushing against the starter or using a breaker bar. The leakage tester has two 100 PSI gauges. One tells mehow much air I am inducing into the cylinder, I use 100 PSI as it is easier to determine %, and the other tells me how much the cylinder I am testing is holding. IF it is holding 90 PSI that is 10%, 80 PSI= 20%, 70 PSI= 30% and so on. So if the cylinder is 10% or less it is a healthy cylinder any more than that it is starting to coke or beginning to have issues. If it has 50% or 60% you have some bad issues. </font></p>
<font color="#000000">I will include one that we found a coked ring on the 2nd ring. What is coking? Carbon is a by product of combustion. So cokingis carbon that builds up around the rings and causes them to stick. In a automotive applications (4 strokes) the rings will rotate and will keep a lot of the carbon from sticking the rings in the ring lands. On a 2 stroke, they have pins that keep the rings from rotating. Because of this I see a lot of rings that will be stuck in the ring groove and willcause high leakage. That is why you need to regularlyrunchemicals like sea foam or Berryman's or anything similar to help prevent it.I will now include some examples..... </font></p>
<font color="#000000">I hope this helps!!!!!!!! </font></p>
<font color="#000000">Ditchdoc666's Engine. The bottom ring was so stuck I had to use pliers and break itto remove it!!!!</font></p>
http://www.chattanoogafishingforum.com/forums/thread-view.asp?tid=27877&posts=27&mid=214730&highlight=150+&highlightmode=1&action=search</p>
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<font color="#ff0033">COMPRESSION TEST</font>......<font color="#000000">What a compression test does is tells you how much pressure that piston/rings can make moving from the bottom of the cylinder to the top. The problem with a compression test is that it is not a real accurate way to determine the health of a engine as it usually has to have a very serious issue to show up on a compression test. I have a insert out of a manual that states if a engine has equal compression and is hard to start or runs poorly, to check for mechanical issues. So even OMC (Johnson/Evinrude) understands this and puts this in their service manuals. All engines work off the same principles. I have dealt with several engines that have passed a compression test and failed a leakage test. </font></p>
<font color="#000000">I mainly use a compression testto help determine what octane fuel that a engine requires. The higher the compression, the more heat is produced in the combustion chamber. This can cause the temperature in the combustion chamber to ignite the fuel instead of the spark plug (detonation). Causing engine damage. The higher the octane, the slower the fuel burns at the same compression ratio. So to get the most out of the fuel, you need to use the correct octane for your compressionas too high of octane will cause a 2 stroke to actually loose power. More on this later!</font></p>
<font color="#ff3300">LEAKAGE TEST</font><font color="#000000">..... First you must understand what happens in a cylinder. The piston begins moving to the top of the cylindercompressing the air/fuel charge making it more flammable.Just before the piston reaches thevery top of the cylinder, spark will occur. (thisknow as timing for example 23* Before Top Dead Center)Just as the piston reaches the top and starts on it's way back down the air/fuelthat has already startedto burn will finish burning creatinga large amount of pressure pushing on the piston thus rotating the crankshaft, drive shaft, and then the prop.So what a leakage test does is check the seal of the piston rings and gasket. Remember whencombustion is happening, there is a large amount of pressure pushing on the piston. If you have a poor seal, then some of this pressure will go elsewhere and the engine will have a power loss. This leakage is also known as blow by. Now that you understand what is going on you can see if you run 93 octane (slower burning) in a engine that needs 87 octane (faster burning) it will mess up the combustion process and cause a power loss. </font></p>
<font color="#000000">What a leakage test does, is induces air into the cylinder as the engine is being held from moving and this tests the seal of the rings and head gasket. What I do is remove all the spark plugs and using ascrewdriver I will rotate the piston to the top and then down 1/2" to 3/4" past theTDC (top dead center)and mark my screwdriver with tapeso all are tested at the same height. I do this as a carbon ring will form at the top of the cylinder and give you a false reading. I will include Ditchdoc666's engine as a prime example of this. I willthen hold the engine with either a pair of vice grips on the flywheel pushing against the starter or using a breaker bar. The leakage tester has two 100 PSI gauges. One tells mehow much air I am inducing into the cylinder, I use 100 PSI as it is easier to determine %, and the other tells me how much the cylinder I am testing is holding. IF it is holding 90 PSI that is 10%, 80 PSI= 20%, 70 PSI= 30% and so on. So if the cylinder is 10% or less it is a healthy cylinder any more than that it is starting to coke or beginning to have issues. If it has 50% or 60% you have some bad issues. </font></p>
<font color="#000000">I will include one that we found a coked ring on the 2nd ring. What is coking? Carbon is a by product of combustion. So cokingis carbon that builds up around the rings and causes them to stick. In a automotive applications (4 strokes) the rings will rotate and will keep a lot of the carbon from sticking the rings in the ring lands. On a 2 stroke, they have pins that keep the rings from rotating. Because of this I see a lot of rings that will be stuck in the ring groove and willcause high leakage. That is why you need to regularlyrunchemicals like sea foam or Berryman's or anything similar to help prevent it.I will now include some examples..... </font></p>
<font color="#000000">I hope this helps!!!!!!!! </font></p>
<font color="#000000">Ditchdoc666's Engine. The bottom ring was so stuck I had to use pliers and break itto remove it!!!!</font></p>
http://www.chattanoogafishingforum.com/forums/thread-view.asp?tid=27877&posts=27&mid=214730&highlight=150+&highlightmode=1&action=search</p>
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