RM forks on KDX

[clw]

Yeah, yeah...got this old KDX and now I've determined that it has a RM front end. The RM forks measure about 1 1/2" longer (top of tube to axle centerline) than the original forks. I checked another guys bike last weekend. Even raising the forks in the clamps the maximum amount it's still 1" too long up front.

Question: These old forks have a lot of preload, can I reduce the preload to a mm or two to get the front end to settle a bit? The front now has a tendency to push, but it is stable! Is there a better way to get the proper attitude back?

 

[Fred T]

Longer dogbones - Devolracing.com

 

[johnf3]

Longer linkage rods in the back will lower the back end, which would make the problem worse.

 

[Fred T]

OK Longer ones then, they sell them too. K?

 

[clw]

Thanks for the suggestions.

Actually a longer rod would raise the back end. It's the old rocker arm arrangement on top of the swingarm. I called a welder friend and he thought he could splice in a chunk of aluminum if I knew how much. It looks like it is about a 3:1 ratio between wheel and shock travel. Does this sound right?
So to jack up say 1 1/4" he'd splice in 3/8"? This would make it a big bike!

Or is there a simple way to limit travel inside the fork? I've read something a long time ago about shortening bikes for the vertically challenged but don't remember if it was simple or not.

 

[marcusgunby]

You will need to find shorter springs and then install a spacer on the damper rod.

 

[clw]

All right! Shorter springs shant be a problem, they already have a 4" or so spacer on top of the spring. So do I just fabricate a new shorter preload spacer (like 3") and then put a 1" spacer on the damper rod to limit the extended travel? Or, should some other compensating adjustments be made? I don't know if I should maybe raise the oil level a bit since there will be slightly less air in the pump (to keep the air volume to travel proportional)? Increase or decrease preload? Am I getting too deep without a test ride?

Thanks again.

 

[marcusgunby]

The spacers sound correct.On the oil level -good question, i would start at 1" lower than spec.Its easy to add oil.

 

[RGalesi]

Talk to a guy named Ricky Carmichael... He probably had to lower his forks too...

Sorry... You're right about the oil... If you make a abrupt change in the amount of air in the fork, it wil heavly affect its performance.

 

[JasonWho]

Nice try FredT, but what do you KTM guys know anyway? :-) Just kidding. The '87 200 doesn't have pull rods. It looks like a mid-80's KX.
Speaking of which, have you considered using an adjustable link from one of those mid 80's KX's? I am not sure if it would help or not.
How far above the top triple clamp can you mount them without bottoming out on the front fender? Perhaps you are familiar with the zip tie around the fork tube trick to determine true fork travel.

 

[clw]

adjustable link?
adjustable link?
I kind of remember seeing one, somewhere. Are these still made/sold?

I can raise the forks another 1/2" or so before they hit the bottom of the handlebars. I should try a real measurement of travel. Man, I'd hate to find out I was wrong and bottom the tire under the fender. An ugly endo, the last one hurt, for a long time!

 

[JasonWho]

Just search on ebay or used parts websites, cycle salvage places, etc. You might want to check www.buykawasaki.com to see which model KX's had the adjustable link.