Hot Rods connecting rod

[shanYE west]

:yelrotflmao: :yelrotflmao:

 

And I hope we all agree that you should have longer rod life due to it being more perpendicular on the compression stroke.

 

Now stop argueing ya bunch of know it alls :beer:

 

 

I agree.

 

 

That sounds like a plan. :thumbsup:

[2strokesmoker]

I agree.

 

 

That sounds like a plan. :thumbsup:

 

Well it was fun while it lasted. I only took three days. :yelrotflmao:

[No Limit Powersports]

These are the kind of discussions that make a good board a good resource for people.

 

The longer rod length does cause the angle of the rod to lessen causing less friction on the piston wall/cylinder wall at the same time giving a mechanical advantage to turn the force applied by the combustion cycle to downward motion to a longer rod but not in all quadrants of the crank rotation. So yes the force applied by the combustion is constant but it will turn the force into motion easier with a longer rod. But in the same hand a shorter rod will keep your port area time open longer and in theory cause the motor to pump more efficiently but the advantages of this can quickly be overcome by the friction loss by too short of rod. LOL this is one of those arguments that can be argued that shorter rods are better and longer rods are better and both be correct lol! So thats the million dollar question, whats the magical ratio.

[Stellar Performance]

6 inches. Or at least thats what I tell my wife is the magic ratio....lol!

[shanYE west]

These are the kind of discussions that make a good board a good resource for people.

 

The longer rod length does cause the angle of the rod to lessen causing less friction on the piston wall/cylinder wall at the same time giving a mechanical advantage to turn the force applied by the combustion cycle to downward motion to a longer rod but not in all quadrants of the crank rotation. So yes the force applied by the combustion is constant but it will turn the force into motion easier with a longer rod. But in the same hand a shorter rod will keep your port area time open longer and in theory cause the motor to pump more efficiently but the advantages of this can quickly be overcome by the friction loss by too short of rod. LOL this is one of those arguments that can be argued that shorter rods are better and longer rods are better and both be correct lol! So thats the million dollar question, whats the magical ratio.

 

Good points :thumbsup: I agree with all of that!

 

I never thought about the port area being open longer with a shorter rod.. It makes sense though..

[shanYE west]

6 inches. Or at least thats what I tell my wife is the magic ratio....lol!

 

 

You just need to find a smaller wife.. You can be 4 inches and get the same ratio... :ninja:

 

 

:yelrotflmao:

[Bansh-eman]

Force has nothing to do with measuring the weight?? then how is force measured? in cheerios?? I have 165 cheerios per square inch of compression. My bike generated 300 cheerio's of torque. Your right.. that is better! :biggrin:

 

 

 

Sorry greg.. but your back pedaling and contradicting yourself.. I underlined your quote.

 

 

 

So which is it greg?.. by your last quote your saying that more angle produces less direct force. (The scale will read less at a angle) Then above you state that less angle produces less direct force...

 

 

Thats why this is pointless becasue you dont even know what point your arguing.. You try to sound like you know what your talking about.. but in the end.. Its all bullshit..

Force is measured in Newton

[Stellar Performance]

I hate to burst your bubble greg. But the amount of force it takes to move something is determined by the amount of resistance it has. So by you stating that the resistance is the same, then the force must be the same.

 

There is a hole in your comparison to the weight on a broom stick over a scale. The piston is limited to only a vertical stroke, staying in a straight line, not being able to shift left or right. The crank shaft can only rotate, not move vertical or horizontal. The rod is strictly being used to connect those two items (all of these things we know). But where your comparison fails is that all of the components you used (weight, broomstick, scale, etc) would have to be setup in a matching enviroment. In other words, the scale would have to be mounted in a fixed position like the crank (not be able to move verticle or horizontal). The broomstick would have to be fixed to the scale like a rod(not being able to slide around freely). And the weigh would have to be fixed to the broomstick (not being able to tilt freely). And if you were able to rig up all of those items as stated. Well I think we all agree that 100 pounds whether it is directly over the scale, or offest by a foot, is still going to weigh 100 pounds.

 

Greg....do not read this and think I am trying to be an ass. Its not meant to call anyone out or say this person or that person is right or wrong. I do think that some times these threads can get interesting. And arguments some times lead to better knowledge for everyone to read. But lets get real. Not one of us graduated MIT with a masters in physics (that I am aware of...lol). Not one of us is going to spend the time and money to do the proper testing to prove their "theory" right or wrong. And in this application because of it being a rotating load at 358 out of 360 degrees of movement, all of our statements of what it true or what is false simply are "THEORY".

 

 

 

I dont understand why everyone is being so hard headed on this anyways...lol. It seems that we all agree on everything except the bearing life being extended. My stand on that stays the same in regards to the most amount of resistance on the bearings, rod, piston, etc is during the compression stroke at TDC when the rod is perpendicular to the crank and piston anyways. So rod length would not change that at all, only combustion area (cc's) would.

 

 

Now let's get some beers and go racing :beer:

 

[Bansh-eman]

I know that the broom stick/scale was not accurate, that

[BellicoseBanshee]

I think Greg was trying to illustrate the i and j components [r(t) = x(t)i + y(t)j + z(t)k] the rod pins experience when force is applied at an angle. The i and j components can be easily illustrated with a free-body diagram of the system. In other words, if the rod is at an angle, the pin is experiencing force in two directions, and the only force that the scale will experience is the force in the j direction. The scale will not experience the resultant force...

[BigRed350x]

The answer to all of your questions is..... 7. That's all there is to it. :geek:

[dajogejr]

You guys lost me at the flux capacitor.

[Stellar Performance]

okay.....now lets go have a drink!!!!

[No Limit Powersports]

With the increased angle from a shorter rod it will put more pressure on the piston wall/cylinder wall friction surface, thats given. Now if we take an increased amount of friction on the wall it will take more force to get the crank to rotate because as Tim said the force to move an object is relative to how much resistance that object has (this is the "for every action there is a equal and opposite reaction").

So in theory yes I feel that a longer rod during certain parts of the stroke is easier on the bearings and most importantly on the piston. But with whats readily available for our motors a short rod (110-115) to a longer rod (120-130) the wrist pin bearing is not the problem anyway so it really not where the short rod/long rod discussion needs to head. We have built several 64mm stroke 73 bore motors with the 115mm rod and they are hard on the pistons skirts but then again we have another dozen variables we can throw in the mix including and most importantly oil so to 100% attribute the piston wear to the short rod would be a inaccurate also.

 

These are the kind of discussions that make me love these boards and not the how fast is my bike and will i out run a raptor!

[shanYE west]

With the increased angle from a shorter rod it will put more pressure on the piston wall/cylinder wall friction surface, thats given. Now if we take an increased amount of friction on the wall it will take more force to get the crank to rotate because as Tim said the force to move an object is relative to how much resistance that object has (this is the "for every action there is a equal and opposite reaction").

So in theory yes I feel that a longer rod during certain parts of the stroke is easier on the bearings and most importantly on the piston. But with whats readily available for our motors a short rod (110-115) to a longer rod (120-130) the wrist pin bearing is not the problem anyway so it really not where the short rod/long rod discussion needs to head. We have built several 64mm stroke 73 bore motors with the 115mm rod and they are hard on the pistons skirts but then again we have another dozen variables we can throw in the mix including and most importantly oil so to 100% attribute the piston wear to the short rod would be a inaccurate also.

 

These are the kind of discussions that make me love these boards and not the how fast is my bike and will i out run a raptor!

 

 

I agree with that.

 

My whole argument was that extended wrist pin and lower rod bearing life would be minimal if any and is not the key benifit to a long rod crank. (IMO the piston skirt wear is the primary benifit for increased life) Loads on the bearings will remain the same with long rods unless resistance is reduced. Long rods dont reduce the resistance they only provied a mechanical advantage against it.

 

But you did make a VERY good point that with reduced side wall friction less resistance will be obtained. :thumbsup: