The real crank balancing answer

[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 ..... ...... 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]

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.

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.

[chevyk30]

Hey guys!  This is kind of funny!!  My name is also Adam, I am new here as well, love the site!! I also have the same question, as I am in the middle of rebuilding the lower end of one of my kx500s, I also appreciate all of your responses!!  keep them coming! 


Adam

[KXcam22]

I have to agree with BDI and Don.  I also don't think that it is worth is unless your are building a high RPM engine.  If the guy who is assembling the crank does a carefull job then the balance, while not perfect, will be very good.  Many of us have concluded that the reason some KX500's vibrate more than others is based on the crank assembly tolerance at the factory.  I would spend my money elsewhere.  Hope this helps. Cam.

[ma71t]

thanks for all the quick responses guys

-Adam

[Mick]

When these bikes were produced they might have had a 60% balance factor.  God only knows what most of yours is nowadays with all the after market pistons, rods and bearings.  Even replacing parts with OEM components will yield different results due to inconsistencies in production.  There is however the slim chance you've actually improved the balance for your particular riding style and ability.

I haven't been impressed by the work I've seen from crankworks.  I've seen them take weight off in several places around the crank halfs.  At 9, 11, 4 and 7 o'clock from the crank pin.  WTF?  And none of the material taken off was the same distance from center.  And I'm not a fan of welded cranks either.

This is a crank I had balanced by Surf 'N Turf out of Connecticut.



Taking the very parts I run and having the ability to balance them to a 56% factor really helped.  It runs smoother everywhere.  How so?  The original parts must have been far from Honda spec.  As the motor was assembled by Service Honda piece by piece.  No fault on S/H, but I don't believe Honda's or Kawasaki's off the shelf parts receive the thorough QC inspection they once used to now that they are no longer produced.
Regardless of who's to blame, the only downside to a balanced crank is money.  It cost me $375.  But it was worth it.  It vibrates much less than I imagined a 500 could be balanced to run.  Yes it vibrates more at some rpm than others, but overall it runs much smoother than you'd think a 500 could.  Big thumbs up!

[js]

has anyone tried to use a heavy flywheel weight to balance the crank. and why wouldnt this work? anyone with a bridgport could lighten up one side of there steahly weight if they knew where to put the holes and the size of hole to get it balanced out. I quess you'd have to mark it to line up with everything. or come up with a new design that locates everytime you put it on. ajustable weights patented in the 30's and hundreds of external balancing patents. uspto.gov if someone need to look up there idea.

[BDI]

Internaly balanced engines work better then externaly balanced engines.That why race engines get balanced internaly.

[KXcam22]

Plus the weight is at the end of one end of the crank which adds additional harmonics and oscilations, many you don't want. Nice dwgs though. Cam.