With all of the talk about un-balanced cranks lately, and some of the other post I've been seeing, I started thinking about what exactly is a balanced crank, and are the Cannondale engine builders actually balancing our cranks, or balancing our engines, and does it matter?
I am by no means an expert on this subject, just trying to learn and get everyones ideas.
First, I'll throw out my definitions:
Balanced Engine: A balanced engine will have the weight matched for the opposing forces in the engine: i.e. The weight of the piston, piston pin, rings, rod, and counterbalance will be matched to the weight of the crank so that as they are spinning opposite each other everything balances out.
Crank balancing: To properly balance a crank, it is installed on a machine that spins the crank at high RPM's that checks for proper balance - similar to balancing a tire. Given that our crank is single cylinder and all the weight is on one side it can't be 100% balanced, however it can be trued and adjusted for best performance in out engines.
From the Falicon website: A single cylinder crank is always unbalanced. The balancing operation we perform moves that unbalance (vibration) to an RPM that is either higher or lower than your engine's RPM operating range. We accomplish this by removing or adding weight to the crank in a location that our balancing equipment has told us to do so. Balancing or "moving the unbalance" really helps a single cylinder crank, especially if it is to be used at sustained high speeds.
OK, so I know from the factory that when the cranks where changed for 03' they where lighter than the old style cranks. Based on my definitions above, this would cause our engines to be out of balance, not necessarily the cranks to be out of balance. The factory corrected this late in 03' by adding weight to the crank.
I just saw a post from Southbay stating These kits have been balanced to the new style crank to prevent the known balance issues associated with the OEM piston kits. which again goes toward balancing the engine.
So my questions are:
Are the cranks themselves in balance, and if not, is anyone doing anything about it?
When the factory added the weight to the 03' cranks to correct engine balance, they put it all on one side. Wouldn't that throw the side-to-side balance of the crank itself out?
How much out of balance can our engines be without causing exsessive vibration and wear? my understanding is that the stock bore piston is 4 grams lighter than the 450 - is this a problem?
Balanced Engine vs Balanced Crank
I might be able to help out here. This can be made as complicated as you like, but for the sake of us all I'll hit the high points and try to keep it on layman's terms. The crank it self can be balanced for a prescribed rpm range It's usually not a problem to achieve this throughout the rpm range we would specify. Esentially the rotational masses are equally distributed around the circumference of the main axis (where the main bearings go). This is why we have a counter weight or balancer to offset the mass of the crank "throw" (where the rod connects). If we spin our cranks to, let's say....20,000 rpm, they may become unbalanced because the crank deforms and the position of the rotational masses move. I don't think we'll ever be running them up to 14,000 much more to 20,000 rpm. So, to have a balanced crank is some what important, because any vibration caused by an unbalanced crank would be transfered to other sytems or components in the engine. An activity called resonance might occur. This is basically when one vibrating system induces another system to vibrate. This is BAD. Now that we have the crank balanced, lets move on to the engine. Our engine will never be perfectly balanced, mainly because it is a single cyclinder system. In fact, most engines are not "fully or perfectly" balanced regardless of the number of cyclinders or arrangement. Our goal here is to minimize any vibration caused by the crank, rod and pistion and most importantly prevent a "critical speed" from showing up in the operating range. The critical speed is a point at which the system will be excited to it's natural frequency. This can cause the crank to deform when compounded by the centrifugal forces while rotating. This is VERY, VERY, VERY BAD and can wipe you engine out in a heart beat and maybe crack or break other things such as the frame. So the key is to move this critical speed outside of the prescribed rpm ranges or not to operate at the critical rpm. The last would not be practical in or case, but in larger engines such as on trains, ships, power plants, etc, it's cost prohibited to move the critical speed(rpm) outside completely of the operating range, and since most of these engines operate at some constant speed, the governing systems won't allow one to set the rpm at the critical speed, only pass through it.
I hope this helps. I've got a headache now.:eek:
I hope this helps. I've got a headache now.:eek:
Swamp, great explanation.
Thomez, based on my definition above, I know Winky is balancing the engine. Is he balancing the crank itself? Dynamically? What method is Southbay using? How about WWE? ATK?
Winky has also discovered some other problems with our cranks, and is addressing those, things like the side clearance on the rod, garbage in the oil channels.
Don't get me wrong here, I'm not knocking any of the engine builders, just trying to get a better understanding of exactly what is being balanced. Based on all the information I've gotten so far, what we're getting is more of an engine balance than a crank balance. Does it really matter?
Thomez, based on my definition above, I know Winky is balancing the engine. Is he balancing the crank itself? Dynamically? What method is Southbay using? How about WWE? ATK?
Winky has also discovered some other problems with our cranks, and is addressing those, things like the side clearance on the rod, garbage in the oil channels.
Don't get me wrong here, I'm not knocking any of the engine builders, just trying to get a better understanding of exactly what is being balanced. Based on all the information I've gotten so far, what we're getting is more of an engine balance than a crank balance. Does it really matter?
good read:
Can a single cylinder crankshaft be balanced? Does it help?
A single cylinder crank is always unbalanced. The balancing operation we perform moves that unbalance (vibration) to an RPM that is either higher or lower than your engine's RPM operating range. We accomplish this by removing or adding weight to the crank in a location that our balancing equipment has told us to do so. Balancing or "moving the unbalance" really helps a single cylinder crank, especially if it is to be used at sustained high speeds.
I just found this somewhere, thought it looked interesting.
A single cylinder crank is always unbalanced. The balancing operation we perform moves that unbalance (vibration) to an RPM that is either higher or lower than your engine's RPM operating range. We accomplish this by removing or adding weight to the crank in a location that our balancing equipment has told us to do so. Balancing or "moving the unbalance" really helps a single cylinder crank, especially if it is to be used at sustained high speeds.
I just found this somewhere, thought it looked interesting.
-
southbaymoto
- Posts: 0
- Joined: Wed Mar 10, 2021 10:41 pm
The counter balancer only assists the crankshaft to help cancel out vibration. The counter balancer was never changed in the engine. Cannondale decided to change the crank specifications for more economical production.
The vendor that mfgs. the cranks and the Cannondale engineers overlooked the fact that the new mfg. process altered the "balance factor". This means the new crank does not match the original balance specifications. Thereby the newer engines have more vibration. The engine needs to be balanced to match the counter balancer in order to true up the balance factor and reduce vibration.
Depending on the style crank you have one of the processes involved in the DE1 kit is to balance the engine. We do this in engines that have the newer style crank by lightening the reciprocating weight in the top end and adding weigh to the crank.
Our piston kit takes in to consideration the balance factor and is matched to work with the newer style crank. This means that there is reduced vibration. It is true that it is completely impossible to balance a crank perfectly. The goal is to reduce the vibration as much as possible. This process used in our dependability enhancement kit that is the skeletal structure for all our performance upgrades.
I can understand how this can be confusing. There is defiantly an issue of semantics in calling it ????????????????balancing the crank??????????????? which raises a point. I guess balancing the engine is a better way to phrase it. Well to the website I have some changes to make. Thanks Jaybr!
Dustin
SBM
The vendor that mfgs. the cranks and the Cannondale engineers overlooked the fact that the new mfg. process altered the "balance factor". This means the new crank does not match the original balance specifications. Thereby the newer engines have more vibration. The engine needs to be balanced to match the counter balancer in order to true up the balance factor and reduce vibration.
Depending on the style crank you have one of the processes involved in the DE1 kit is to balance the engine. We do this in engines that have the newer style crank by lightening the reciprocating weight in the top end and adding weigh to the crank.
Our piston kit takes in to consideration the balance factor and is matched to work with the newer style crank. This means that there is reduced vibration. It is true that it is completely impossible to balance a crank perfectly. The goal is to reduce the vibration as much as possible. This process used in our dependability enhancement kit that is the skeletal structure for all our performance upgrades.
I can understand how this can be confusing. There is defiantly an issue of semantics in calling it ????????????????balancing the crank??????????????? which raises a point. I guess balancing the engine is a better way to phrase it. Well to the website I have some changes to make. Thanks Jaybr!
Dustin
SBM