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Old 07-31-2010, 10:46 AM   #16
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It would make a purdy paper weight though.
lol. no i cut to much weight out probably just blow away. it weigh 37g
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Old 07-31-2010, 11:00 AM   #17
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it is a sirio longstroke 5+2 so it came it the silicone putty. for the people that dont think cuting groves in the outer crank dose anything it increase pressure in the crank wich lest you run less fuel. a high counterwieght crank is only help to speed. balance dose noting i can put a heavy flywheel on if i want to stop vibration but it will ear up what iam trying to do the motor has more power than it need. the only thing i need is fuel mileage.
I agree i think those small things you are doing well help. These motor are hard to make un-balanced I do alot to stock cranks myself and have never had a problem. I think your mods look good and im sure myself that they well help runtime and bottomend. I hope you keep up the work bud i love moding my motors. Speedy
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Old 07-31-2010, 12:17 PM   #18
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I am not sure why people say you can't balance a single cylinder engine. Yes on multiple cylinder engines they make sure the piston and rod are all the same wieight to each other. But on 8 cyl motors they also have a formula to calculate the total weight of the piston rod, rings etc. to get the right bob weight on the crank.

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Old 07-31-2010, 01:03 PM   #19
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I am not sure why people say you can't balance a single cylinder engine.
Because you can't. The perfect "balance" changes depending on crank position, rpm, etc. Multi cylinder engines compensate for this automatically (well some do). As one piston is going up, another is going down and the changes mostly even out.

You actually would NOT want to match counter weight to piston/rod weight. It would vibrate like crazy at high rpms.
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Old 07-31-2010, 01:13 PM   #20
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i guess it all depends on what a person is defining by the term balancing....Engine harmonics is a very advanced subject that goes much deeper then just the general term balancing ! in the end the entire goal is to make the engines vibrate the least amount possible...the only way to really do this is using some very advanced equipment and testing the engines in actual operation....
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Old 07-31-2010, 02:22 PM   #21
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Because you can't. The perfect "balance" changes depending on crank position, rpm, etc. Multi cylinder engines compensate for this automatically (well some do). As one piston is going up, another is going down and the changes mostly even out.

You actually would NOT want to match counter weight to piston/rod weight. It would vibrate like crazy at high rpms.


Did I say match the weight? I don't think any motor no matter how many cylinders can be perfecly balanced.

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Old 07-31-2010, 03:03 PM   #22
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I don't think any motor no matter how many cylinders can be perfecly balanced.

Rex
Some configurations are better than others. For instance, V10's are known for being an inherently well balanced design. When F1 switched to V8's, vibration above 19k rpm became a MAJOR problem so the FIA actually limited them for reliability. Straight 6, flat six and V12's have NONE of the four main vibrations and are therefore the smoothest of all.

The general consensus with go kart motor builders is that somewhere between 48-60% balance works best. Since our motors turn twice the rpm, our needs may be different but that is still a big margin to work within.
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Old 07-31-2010, 03:17 PM   #23
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I guess thats why most hi-rpm, big horsepowered
multi-cylinder engines use a rather large harmonic
balancer. Not to mention a counter-weighted flywheel
also. Whats going to be the next big thing in rc nitro
engines, a fluid filled harmonic balancing flywheel ?
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Old 07-31-2010, 03:23 PM   #24
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Originally Posted by rageworks View Post
I guess thats why most hi-rpm, big horsepowered
multi-cylinder engines use a rather large harmonic
balancer. Not to mention a counter-weighted flywheel
also. Whats going to be the next big thing in rc nitro
engines, a fluid filled harmonic balancing flywheel ?
That's because V8's are terrible in terms of balance. A flat twin is better (and they aren't all that good either).

As for our motors, balance isn't that big a problem. The flywheel actually dampens a lot of it and what is left isn't a problem. I mean you don't see us breaking cranks left and right do you?
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Old 07-31-2010, 03:36 PM   #25
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Originally Posted by wingracer View Post
Some configurations are better than others. For instance, V10's are known for being an inherently well balanced design. When F1 switched to V8's, vibration above 19k rpm became a MAJOR problem so the FIA actually limited them for reliability. Straight 6, flat six and V12's have NONE of the four main vibrations and are therefore the smoothest of all.

The general consensus with go kart motor builders is that somewhere between 48-60% balance works best. Since our motors turn twice the rpm, our needs may be different but that is still a big margin to work within.
I believe the angle of 92 or 94 degrees within the V-shape is the magical number to minimize the vibrations and other forces. Several F1 engine manufacturers have tried it all but all do come back to this magical number.
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Old 07-31-2010, 04:20 PM   #26
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Originally Posted by wingracer View Post
Because you can't. The perfect "balance" changes depending on crank position, rpm, etc. Multi cylinder engines compensate for this automatically (well some do). As one piston is going up, another is going down and the changes mostly even out.

You actually would NOT want to match counter weight to piston/rod weight. It would vibrate like crazy at high rpms.
Go ahead and cut a some of weight out of the counter balance of a motor, reassemble and start it then tell us that a single cylinder is not balanced or can't be balanced. This is why it is called a "counter weight" or "counter balance", It should be pretty darn close to the weight of the piston and rod along with other variables that take place.
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Old 07-31-2010, 04:37 PM   #27
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i got a question for you guys....why did O.S. make the crank like this in there .28xz?

its basicly a solid chunk ....stock on the right, the one i modded on the left.
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Old 07-31-2010, 05:54 PM   #28
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Originally Posted by NitroFreak2 View Post
Go ahead and cut a some of weight out of the counter balance of a motor, reassemble and start it then tell us that a single cylinder is not balanced or can't be balanced. This is why it is called a "counter weight" or "counter balance", It should be pretty darn close to the weight of the piston and rod along with other variables that take place.
counter weight of the is not the counter balance. the more counter weight will not give you more balance what it dose is give you more mass. the mass will help stop vibration not because it even balance because it weighs more. counter balance it counter the compression wich is not never even.

to prove this right think of it this way if you have two cylinder you would balance the crank than you would balance the piston. the motor is still not balance because the piston compress at different time even if you make the pistons compress at the same time even form each other still one piston will make more compression than the other. the only to help is to add weight. wind you add weight to the opposite of the piston it like time 5 what the flywheel. unless you counter flywheel. all the weight you add will slow down your acceleration and fuel mileage. wich the last time i look acceleration and fuel mileage is what you need the most in offroad rc racing. but dont get me wrong you still haft to have some counter weight.
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Old 07-31-2010, 08:35 PM   #29
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Originally Posted by NitroFreak2 View Post
Go ahead and cut a some of weight out of the counter balance of a motor, reassemble and start it then tell us that a single cylinder is not balanced or can't be balanced. This is why it is called a "counter weight" or "counter balance", It should be pretty darn close to the weight of the piston and rod along with other variables that take place.
I have done it many times with no problems. If the counter weight was the same as the piston/rod etc. weight you would have a crap engine. You want the counter weight to be LESS than the weight of the reciprocating mass by a certain percentage. I don't know what that percentage is on our motors but on go kart motors it is usually between 48 and 60%.

Think about it for a second. The reciprocating mass (piston, wrist pin and clips and a percentage of the rod) move up and down (vertical plane). If you match the counter weight to that, you will have mostly balanced the up and down mass of the motor. Not completely but pretty close. The problem now is that you have that highly weighted crank rotating, not reciprocating. This will be massive imbalance in the horizontal plane as opposed to the vertical plane of the reciprocating mass. In this case all you have done is change the plane of the vibration, not reduced it all. You will have just as much side to side vibration as a completely non-counterbalanced crank would have up and down. By using a lighter counterweight crank, you can partially dampen the vertical plane and not throw the vertical plane so far out of whack.

Now please understand, I am not saying you need NO counterweight. Some is absolutely necessary for a good running engine. What I am saying is that this myth that a one cylinder motor can be perfectly balanced and must maintain that exact balance in order to run well is completely false. It needs to be within a certain range, but an exact number is not required.
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Old 08-01-2010, 01:39 AM   #30
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Originally Posted by absolutemayhem View Post
i got a question for you guys....why did O.S. make the crank like this in there .28xz?

its basicly a solid chunk ....stock on the right, the one i modded on the left.
Did you notice something after the mod?

Be clear about one thing, no manufacturer does put the ideal engine on the market. The best engine will take a lot of work which takes to long production time and that is why manufacturers are choosing shapes they can create in a short time with as less tools possible.
Beside that, you did take away some volume of the crank making the crankcase volume larger and that is affecting the bottom power.

About the counterweight. it is on a different distance from the center than the piston so there is no use to make it in balance with the weight of the piston/rod. Rotating forces are build up depending the distance from the center and beside that you have the forces from the compression and combustion to take with it. I have heard that indeed somewhere a balance of 1/3:2/3 is needed.
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