KX500 balanced crank?

[69HemiGTX]

Maybe some of you open class guys can help me here. I am looking for input about balancing cranks on non-counterbalanced two stroke engines, especially CR and KX 500s. I am trying to find out how much they reduce vibration when placed in a quad frame. Yes, I am asking a question relevant to ATVs, but this applies to bikes, too. I am coming around to the idea of a KX500 powered quad again (I've wanted to build this for years but couldn't afford it), so that's why I am asking about crank balancing. A KX500 could shake so bad that it kills unborn children, and I don't want any of that. If worse comes to worse, I already have blueprints drawn up for a rubber mount system. I just want something very different from the thousands of Hondas I see everytime I am at the dunes. Plus, I'm a Kawasaki guy, and I'm sick of not having any good "true" Kawasaki powered quads, excluding the V-Force. I don't want a V-Force because of the auto tranny or a Tecate because thay are too hard to find parts for. Any help would be greatly appreciated.

Ooops, I forgot to mention the type of riding I'll be doing and powerband I am in search of. I will ride almost exclusively in the dunes. I will venture to a motocross track every once in a while, but will be on the sand 95% of the time. I live four miles from Little Sahara in Oklahoma. I prefer a low-to-mid powerband. I hate drag racing, so top-end really isn't imporatnt to me at all. Torque means a lot because I average about 220lbs. most of the time.

 

[Camstyn]

I looked into this while I had my KX500, the consensus that I got was that you could basically balance it to run smooth at a certain RPM range. Mine ran fairly smooth at low-mid RPM's but would vibrate horribly at high RPM.

I could be wrong but that was the information offered to me at the time, can't remember the source.

 

[gwcrim]

Camstyn is right about the balancing for a certain range of RPMs.

Maybe it's just that my other bike is a Sportster but.... I don't think my KX5 vibrates a lot.

 

[Ol'89r]

I looked into this while I had my KX500, the consensus that I got was that you could basically balance it to run smooth at a certain RPM range..

69HemiGTX.

Cam is correct. You can't balance a crank for all rpm ranges. Since you are dealing with two different forces, Rotating weight, (round and round) and reciprocating weight, (up and down).

The best that can be done is to determine what rpm range the engine will be run in most of the time then, balance it for that range. This is done by using a balance factor.

The engine will vibrate a little above that range and below that range but, will smooth out when within that range.

Just my & .02

Ol'89r

 

[DGMAX99]

For some reason, anytime I get my 500 above idle, vibration is not an issue... more like survival!!! :yikes: :nener:

 

[cujet]

Having spent quite a bit of time with an ACES balancing setup on 2 stroke engines, I can say without reservation that it is impossible to achieve smooth operation. There are those who will say that it can be made smooth at any single and specific RPM, discounting low RPM's of course. That simply is not so. If you spend some time thinking about what is going on with the various internal forces, you will come to understand why this cannot be done.

However, all is not lost. The KX500 engine is a vibration monster. It seems Kawasaki did not do the best job possible in the first place, so there is room for improvement. The Honda CR500 engine is somewhat better, but it can be improved upon also.

As I have mentioned here before, I spent some time with my equipment understanding X and Y axis accelerations on my Husky 360 2 stroke. I was able to modify the balance factor for a smoother overall experience.

Quite simply, by changing the balance factor you will move vibration from one axis to another on a single cyl engine (fore and aft vs. up and down). Certain chassis will respond better in one direction than the other.

The rubber mounting solution is actually a good one. It is almost too bad the engines do not have enough beef on the mounting flanges to accept a proper rubber bushing.

Chris

 

[Hogwylde]

I don't know why everyone thinks that KX500 vibrates so much. Mine doesn't feel like it does. Especially enough to "kill unborn children". Granted, I'm not the first owner of my 93....but Eric Gorr went through my engine last year (i didn't request any special balancing) and I think it purrs along just as smoothly as any other 2 stroke I've ridden.

 

[69HemiGTX]

Thanks for the replies, y'all. I have recieved an email from a European quad builder who uses KTM 560 engines, and he said that he rebalances the cranks and rubber mounts the engine, which almost eliminates vibration. I think I will try the same approach, although I don't think "eliminating" the vibration is attainable. I expect to still have some, just not enough to make me reconsider the project. Most of it will come through the swingarm bolt because it cannot be rubber mounted there. I think that having the crank balanced will help greatly. I can understand why Kawasaki would have not been more stringent with their balance factor: cost. It would have been cost prohibitive to be very precise, so they just determined an acceptable range, and stuck with it. As far as my comment about "killing unborn children," I said that because the geometry of ATV frames tends to amplify harmonic resonance (vibration). I have ridden a drag quad with a CR500 engine in it (solid mounted), and it was like a paint shaker. Absolutely untolerable for long periods of time. My hands and feet were numb within two minutes. It was fun, but I looked like this: :laugh: Like I said before, I hate drag racing, so I will be riding for more than a few minutes at a time, so comfort is at a premium. Some of my ideas for reducing the vibration are balancing the crank, rubber engine mounts, Faast Company brass bar-end inserts, and rubber handlebar mounts. I understand that this will be a long and expensive process, but I am willing to do it. The ends justify the means in my eyes. Thanks again!


I almost forgot this. Stupid question, but what is the maximum rpm that a 500 is designed to turn? I prefer bottom-to-mid power, so max revs for me will be down from peak. What rpm range would that put my engine in?

 

[cujet]

The 500's generally do not make power above 7500 RPM without serious porting. with the meat of the power around 6500. BTW, the LT500 Suz engine is counterbalanced. While they are troublesome if modified for more output while everything is stock, there is a wealth of info out there as to what needs to be done to eliminate the weak spots. Cylinder studs come to mind. Not too big a deal to make them a nice, powerful, smoother, reliable engine.

Chris

 

[69HemiGTX]

So I guess my rpm range would be from about 3000 to 6500? I am very familiar with the LT500R. Hell, I've owned four! Most of their weak spots are the lower cylinder bolt bosses, main bearing bores, and second gear. I love Quadzillas, but I want something no one else has. I might be one of maybe 20 people in the world with a KX500 powered quad when I'm done, and that suits me just fine. Do you think the Faast Company bar-end inserts would actually help? I know a lot of desert racers use them.

 

[nephron]

I'm like Crim in that I honest to God don't notice ANY vibration. Probably for similar reasons. Maybe I don't care if it vibrates? Maybe I consider it a good trade-off? Maybe it's because everything on a farm is louder than hell and vibrates like a jackhammer? I don't drive a Lexus. I guess I don't get why anyone would literally want to modify their motor to keep it from vibrating. I don't think Pedregon ever has considered it. ;)

 

[gwcrim]

Do you think the Faast Company bar-end inserts would actually help? I know a lot of desert racers use them.

I know of a lot of Harley riders who have tried everything from lead shot to rolls of nickels to bar snakes. From what I've heard, none of them were real effective.

I changed to a different bend of handlebars (2" higher on my Sportster) and noticed a big drop in vibes.