ok ive made a cylinder from a three inch piece of cast its three inch's long and the bore is about 1" +or- how do you measure for the crank throw. oh im hoping that this will be a gas engine. no plans just what ever i can figger in my head & by reading stuff here & there. i think that i measure from the top dead center to the bottom of the cylinder . is that kinda close then divide that in half to make the crank throw.
piston & rod ,crank
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Bogstandard
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Sid,
For an ic engine it is a little more difficult as you have to allow for compression ratios, valve clearances etc. Unless you build all that into the head.
For a straight single acting air/steam engine, measure the length of the cylinder - a, measure the length of the piston - b, subtract b from a, then divide by 2. That will give exact crank throw, where the top of the piston is at the top of the cylinder on the forwards stroke, and the lower edge of the piston skirt is exactly at the bottom of the cylinder at full rearwards stroke. It is always better if you reduce that throw slightly so that you don't hit the extremes.
Confusing isn't it.
John
For an ic engine it is a little more difficult as you have to allow for compression ratios, valve clearances etc. Unless you build all that into the head.
For a straight single acting air/steam engine, measure the length of the cylinder - a, measure the length of the piston - b, subtract b from a, then divide by 2. That will give exact crank throw, where the top of the piston is at the top of the cylinder on the forwards stroke, and the lower edge of the piston skirt is exactly at the bottom of the cylinder at full rearwards stroke. It is always better if you reduce that throw slightly so that you don't hit the extremes.
Confusing isn't it.
John
Cedge
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Itowbig
Having recently done my first engine with a standard cylinder design, I had to work my way through this too. I determined I wanted a 1 inch stroke using a piston that was 1/2 inch in length. I also wanted a 1/16 inch space at each end to accommodate the incoming port. I worked it out by adding the measurements together to come up with a cylinder bore length of 1 5/8 inches. The Crank was designed with the 1 inch stroke in mind by moving the crank pin 1/2 inch from its center axis.
The selected piston rod length was arbitrary and chosen for visual balance and clearances at the stuffing box. I let this rod and the crank determine where my cylinder would have to mount, by setting the piston to the center of the bore. I then checked this at both ends of the stroke to assure the 1/16 inch gaps were equal. Not being a math whiz, I opted for a pragmatic real world approach so that my tiny brain got visual verifications all along the way. This would work with a connecting rod, although I do know there are formulas somewhere for the "best" length in a given setup.
I can't help with the IC idea, as it's not an area I've explored.
Steve
Having recently done my first engine with a standard cylinder design, I had to work my way through this too. I determined I wanted a 1 inch stroke using a piston that was 1/2 inch in length. I also wanted a 1/16 inch space at each end to accommodate the incoming port. I worked it out by adding the measurements together to come up with a cylinder bore length of 1 5/8 inches. The Crank was designed with the 1 inch stroke in mind by moving the crank pin 1/2 inch from its center axis.
The selected piston rod length was arbitrary and chosen for visual balance and clearances at the stuffing box. I let this rod and the crank determine where my cylinder would have to mount, by setting the piston to the center of the bore. I then checked this at both ends of the stroke to assure the 1/16 inch gaps were equal. Not being a math whiz, I opted for a pragmatic real world approach so that my tiny brain got visual verifications all along the way. This would work with a connecting rod, although I do know there are formulas somewhere for the "best" length in a given setup.
I can't help with the IC idea, as it's not an area I've explored.
Steve
C
Circlip
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Not only is Sid confused, but me also. Thought he said "Gas" engine? Shouldn't "Over square" or "Under square" ratios come into play? and forget stuffing box. ??? :-\
Regards Ian.
Regards Ian.
