Fork Swap: KX80 forks on a KDX80

Magellan

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#1
Originally posted in the minis forum, but got no responses there.
Thought I'd try here. Apologies for the cross-post.
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Picked up a decent (i.e., running) kdx80 for my son who has outgrown his XR70 and is ready to move up to a clutch. For $250 it was a good buy, even if does need a little work.

One of the things I wanted to do is to put a set of KX80 forks on it. Primarily to get him a disc brake up front, but the improved suspension would be nice as well.

I picked up the forks, triple tree, and brakes for $99 off eBay (that included shipping).

I'll have to shorten the forks a bit and slide them up in the tree, but I think I can keep the length close to what the KDX had stock.

What is causing a bit more of a problem is finding a 16" rim to lace to the KX hub. The stock KDX rim has 32 spokes. The stock KDX hub has 28.

I can find 32H hubs, but they are spendy and way overkill for this application. I would like to keep the 16" wheell size, but I could be talked out of it.

Will a 17" wheel affect the steering geometry much? Any negative side effects?

I'm going to be hard pressed to keep the bike's stance close to stock as it is given the KX forks are longer. I haven't received them yet, so I don't know how much travel I have to work with. I'd like to keep the 5" of stock travel and I think the forks are 4 or 5 inches longer, so I need at least 8" of travel in the KX forks to accomplish that (I can slide them up about 1" and remove 3 " of travel).

Anyone know of other hubs that will work that are 32H? Or a source for rims? I tried Excel and DID, but couldn't find anything.

Thanks,

mag
 
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#2
Magellan said:
Will a 17" wheel affect the steering geometry much? Any negative side effects?
This is all I'm even close to qualified to answer on this question: Answer is: theoretically, yes. In real life, probably not much. But you can likely negate any change if you can use a lower profile tire. The O.D. of the 17" rim is only 1/2" greater distance from the center of the axle, so a change in the tire may bring it back very close to original OD of the tire you were running on the 16" rim. But if you are running forks signficantly longer than what you were running, the geometry of the bike will be so vastly different than what you had, I doubt the 1/2" difference in your rim will be your problem.
Good luck !!
 

Magellan

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#3
Thanks.
I think I'll just go with the stock KX wheel. Probably the cheapest route and I agree that I have bigger changes to deal with.
 

Magellan

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#4
Done...Finally

Didn't start working on the bike till this spring. Spent the fall and winter collection parts.

I stripped it all down and repainted the frame Kawi green and painted the swingarm and pegs silver.

I had to have the cylinder re-plated. I probably could have run it as it was, but there was a small nick near one of the parts and the plating was work through in a few spots. Add $360 for re-plating, piston, and rings.

Replace all the bearings in the chassis: wheels, swingarm, linkage and shocks.

Put the KX 80 front end on it. I ended up picking up some bronze bushings and turning one down on a lathe so I could use the stock KDX80 steering bearing races on the KX80 stem. That was overall pretty straightforward. I also had to mill the nut on for the triple tree (one just above the bearings) a bit so that it would all bolt up and still have enough threads for the final not on the top of the triple tree.

I shortened the KX80 forks (these are the damper rod ones) with a 4 inch spacer. The stock KX65 for springs are the same rate as the KDX80 springs and are 4 inches shorter. Picked up a set off flea bay, threw in some new seals, and the front end was almost done.

I picked up a '00 wheel, not realizing it was a bit wider than what I needed. I have it working for now, use some inner races from the old wheel bearings as spacers. I'll make some spacers for it later. I had painted the hub and don't feel like doing another wheel. New spacers will be easier.

Rebuilt the rear wheel using a KTM 65SX rim and custom spokes from Buchannan.

New front Maier fender. I have a Maier fender for a KX80, but again, it is the wrong year and isn't a good fit. I may try to modify it, but for now, the original fender is on the bike. Picked up a good looking used tank off flea bay to complete the plastic. (side panels are orig, but not in bad shape).

Cleaned up the carb and treated it to new gaskets.
Need some new bars. Came with some ugly blue anodised bars that we're using for now.

So, the $250 bike ended up closer to $1800 after all the parts (including new tires). My son rode it for the first time today in the yard. Took him a few tries to get the clutch down, but he loves it. It starts first kick and runs really sweet.

I'm in the market for a better rear shock. I think maybe a KX80 shock will work and it would be good if I could add an inch to the back. I have the fork tubes slid up an inch, but the bike could be a bit taller fro my son.

I'll post some pics later.
 

Magellan

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#5
Pics here....


<table style="width:194px;"><tr><td align="center" style="height:194px;background:url(https://picasaweb.google.com/s/c/transparent_album_background.gif) no-repeat left"><a href="https://picasaweb.google.com/113931087230982047644/KDX80?authuser=0&authkey=Gv1sRgCO6WwJnV0s_Ofg&feat=embedwebsite"><img src="https://lh3.googleusercontent.com/-lu79Sbxf19E/UZ2l8_HTFME/AAAAAAAAGf0/bUEMCYVk4HE/s160-c/KDX80.jpg" width="160" height="160" style="margin:1px 0 0 4px;"></a></td></tr><tr><td style="text-align:center;font-family:arial,sans-serif;font-size:11px"><a href="https://picasaweb.google.com/113931087230982047644/KDX80?authuser=0&authkey=Gv1sRgCO6WwJnV0s_Ofg&feat=embedwebsite" style="color:#4D4D4D;font-weight:bold;text-decoration:none;">KDX80</a></td></tr></table>
 

WoodsRider

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#6
Looks good. This spring I finished building a '78 XR75 with CR80 suspension (and a few other mods) for my son to race the PacNW VMX series.