revelstone
Member
i think the following should go on the noob thread but now i cant find it. i had a hard time with the following, but only because i WANTED to be right. i think i got it now.
HOW MANY CC IS THAT ENGINE, ANYWAY???
After a lot of research I finally found the answers I need.
How to calculate the cc of an engine. Especially 2-strokes.
There I was walking down the street when I see this old snow thrower, dead by the side of the road. I think, "I can save you, little engine! But can I legally use you in the state of Utah?"
The whole mystery for me was am I supposed to measure from Top Dead Center (TDC) to Bottom Dead Center (BDC) or am I supposed to measure from TDC to when the exhaust ports are uncovered on the down stroke, thereby releasing the pressure of the explosion of the fuel and air. I called Day Power Equipment. All they do is fix yard equipment from riding lawn mowers to the smallest weed trimmer you can imagine. Day Power Equipment mechanics informed me that stroke on a 2-stroke is measured from TDC to BDC, thereby clearing up just one more of life's little mysteries. I knew this was the case on a four stroke, but having limited experience with 2-strokes, I had to make sure.
The only other problem is how to measure this stuff. I took off the muffler on the little engine, rotated the crankshaft by hand, and stuck a wooden Popsicle stick in the port across the top of the piston. Then I marked the Popsicle stick with a pencil and measured the mark to the end of the stick with a ruler. Same thing with stroke of the engine. Remove the spark plug and turn the crankshaft by hand. When you feel the stick at BDC, mark the stick. Rotate crankshaft again till you feel TDC. Mark the stick again and measure between the marks. This is the stroke.
Normally you measure engine volume in cubic centimeters although engine dimensions are often shown in millimeters. You need to convert any measurements into centimeters before starting the calculations. To convert millimeters to centimeters divide millimeters by 10. 34 millimeters become 3.4 centimeters.
The volume of a cylinder is calculated by multiplying the area of the bore of the cylinder by the stroke. The bore area is calculated as follows:
Bore Area = Bore x Bore x pi / 4. (Pi has a value of 3.14159)
Example:
Bore Area = 4.0 x 4.0 x 3.14159 = 50.26
Bore Area = 50.26 divided by 4 = 12.57
Bore area is therefore 4.0 x 4.0 x 3.14159 / 4 = 12.57 square cm.
Cubic capacity is 12.57(bore area) x 3.8(stroke) = 48cc
Stroke on a 2-cycle engine is Top Dead Center (TDC) to Bottom Dead Center (BDC).
I hope this information helps some other NOOB, making his or her entry into motored bicycles easier.
Revelstone
P.S. I can't use the little snow thrower. According to my calculations, it's 108cc. 49cc is the legal limit in Utah. So I'm giving the engine to a friend of mine for a go-cart he's making.
HOW MANY CC IS THAT ENGINE, ANYWAY???
After a lot of research I finally found the answers I need.
How to calculate the cc of an engine. Especially 2-strokes.
There I was walking down the street when I see this old snow thrower, dead by the side of the road. I think, "I can save you, little engine! But can I legally use you in the state of Utah?"
The whole mystery for me was am I supposed to measure from Top Dead Center (TDC) to Bottom Dead Center (BDC) or am I supposed to measure from TDC to when the exhaust ports are uncovered on the down stroke, thereby releasing the pressure of the explosion of the fuel and air. I called Day Power Equipment. All they do is fix yard equipment from riding lawn mowers to the smallest weed trimmer you can imagine. Day Power Equipment mechanics informed me that stroke on a 2-stroke is measured from TDC to BDC, thereby clearing up just one more of life's little mysteries. I knew this was the case on a four stroke, but having limited experience with 2-strokes, I had to make sure.
The only other problem is how to measure this stuff. I took off the muffler on the little engine, rotated the crankshaft by hand, and stuck a wooden Popsicle stick in the port across the top of the piston. Then I marked the Popsicle stick with a pencil and measured the mark to the end of the stick with a ruler. Same thing with stroke of the engine. Remove the spark plug and turn the crankshaft by hand. When you feel the stick at BDC, mark the stick. Rotate crankshaft again till you feel TDC. Mark the stick again and measure between the marks. This is the stroke.
Normally you measure engine volume in cubic centimeters although engine dimensions are often shown in millimeters. You need to convert any measurements into centimeters before starting the calculations. To convert millimeters to centimeters divide millimeters by 10. 34 millimeters become 3.4 centimeters.
The volume of a cylinder is calculated by multiplying the area of the bore of the cylinder by the stroke. The bore area is calculated as follows:
Bore Area = Bore x Bore x pi / 4. (Pi has a value of 3.14159)
Example:
Bore Area = 4.0 x 4.0 x 3.14159 = 50.26
Bore Area = 50.26 divided by 4 = 12.57
Bore area is therefore 4.0 x 4.0 x 3.14159 / 4 = 12.57 square cm.
Cubic capacity is 12.57(bore area) x 3.8(stroke) = 48cc
Stroke on a 2-cycle engine is Top Dead Center (TDC) to Bottom Dead Center (BDC).
I hope this information helps some other NOOB, making his or her entry into motored bicycles easier.
Revelstone
P.S. I can't use the little snow thrower. According to my calculations, it's 108cc. 49cc is the legal limit in Utah. So I'm giving the engine to a friend of mine for a go-cart he's making.
Last edited by a moderator:
what wasn't clear to me was what and where to measure. appriciate the help 
