Maintenance & Technical > KX500 Original

The real crank balancing answer

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ma71t:
ok this might sound stupid but im looking for the straight up answer..... ive read every post about crank rebuilding and balancing on here and it seems as though some of you guys are all about "balancing" the crank, now i called crank works and they were agreeable with my questions about balancing then i called pro-action and their motor guy tells me "cranks are balanced at the factory and there is no need for it....crank works jsut lightens the crank" , as it sits im in the middle of making the decision to have my crank rebuilt & trued w/ the wiseco hot rod which i already have purchased and leave it at that, or since i will be using the bike primarily as a supermoto on the road ..... :evil:...... should i have the crank "balanced" if there is such a procedure
im well educated on the inner workings of a motor and im still a little bamboozled how you can "balance" a single cylinder motor without a separate couterbalancer....anyways what im looking for is a little insight on the subject and whether or not its worth my $200 through crankworks to have this done

thanks guys....love the site btw

-Adam

BDI:
At a certain RPM the crank halves will start moving away and towards each other due to their weight.  This will cause bad vibration, when you lighten the crank halves you can move the point at which this happens higher up the RPM range but removing metal from the crank will lower primary compression ratio and can cause you to loose some horsepower.  For a motor that spends alot of time in the higher RPM'S this might be something you would consider. There are other reasons and ways to change the weight of the crank and I am sure Doordie or Stewart would be more than happy to give you the reasons why you should or should not do this. 

kaw rider:
there is no such thing as a perfect balanced single cylinder crank. since we don't have a counter balancer. you have to balance it in the rpm range that you spend the less time in. or balance it below 1,000 rpm or higher then 9,000 rpm. i would spent the $200 to have it balanced.

A single cyl motor can never be truly "balanced"
Some of us have enough experience with them to know what kind of "balance factor" to use so there is very little vibration in the operating range we "tune" it for.
A counterbalancer is a MUST

BDI:
I myself have a real hard time justifying spending the money on it. If I road raced the bike I could understand balancing the crank for some sustained high rpm use. If I wanted to lighten the crank so that it would rev faster I would just take the weight off the flywheel and save my primary compression. I could never justify balancing it for low rpm use where I don't think it would really help anything other then rider comfort unless you planed on using the engine in a parking lot striper. I'm sure there are people who can give some really great reasons to do it but given all the pros and cons I think I will be spending my money elsewhere and it sure will not be on welding the crank either.

don46:

--- Quote from: BDI on February 18, 2008, 02:07:11 PM ---I myself have a real hard time justifying spending the money on it. If I road raced the bike I could understand balancing the crank for some sustained high rpm use. If I wanted to lighten the crank so that it would rev faster I would just take the weight off the flywheel and save my primary compression. I could never justify balancing it for low rpm use where I don't think it would really help anything other then rider comfort unless you planed on using the engine in a parking lot striper. I'm sure there are people who can give some really great reasons to do it but given all the pros and cons I think I will be spending my money elsewhere and it sure will not be on welding the crank either.

--- End quote ---

Totally agree, maybe if I was going to make a dual sport out of the K5 I might just for rider comfort. If you get it balanced for a given RPM range it will be smoother there but probably worse at other RPM's, I think the factories use a facto of around 60% from what I have found out, I to was looking into the balance thing and came to the conclusion that it would be a waste for me. I would spend the money on truing, since your installing a new rod anyway make sure the crank is spot on, that will give you less vibes and appear to be smoother.

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