BUILDING A KX500AF with a 2007 KX250F chassis

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I have read several on other builds that have been done and I think I can do it even though I have never tried anything like this before.
I don't have any special training or really cool tools.
I can't weld for beans and certainly not aluminum.
Yet, I think I can do it.
Here is what I started with:


Bye bye Donor bike






Too late

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To see how the engine would sit in the frame I removed the engine mount off the frame.
Now you see it.....


Now you don't.....


I used my Sawsall with a fine metal cutting blade.
Then, after I removed the mount I used a hand grinder and then a orbital sander to smooth it out.
I know it's not necessary as nobody will see it.
Yet for some reason I will feel better

I went ahead and purchased some brand new engine cases for my engine build.
As some of you probably know the left crank shaft bearing journals get really worn and sloppy on K5 engines.
I don't want to do another build any time soon so I might as well do it right to begin with.
This left me with a nice set of blanks for my Mock Up Engine.
I Installed a back up cylinder and head on the old cases and ended up with a good mock up engine.

You will need to drill the rear engine mount holes on the back of the case to make way for the 17mm Pivot bolt.
Do not use a 17mm drill as it is not large enough.
Instead get a 43/64" as it is 0.672" or 17.06 mm.
This is only .01mm or 0.0004" larger than the holes in the frame.
Drilling the cases was a little intimidating but as it turns out it was really fairly easy.
With the hole drilled out I set the engine in the frame to see what all needed to be done next.


Now that I see how it fits, it's time to cut some more on the frame.

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A little measuring and cutting and you now have plenty of room for your engine.
Keep all the pieces you removed as you will need some of them for later


Next

Next

Next

Now.... it is too late

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Just for grins I went to mount the Swing arm to the engine and frame.
Guess what? It does not fit.
The engine cases measured 94.3MM or 3.713".


The inside to the inside of the swing arm bushings when pushed toward the center as they would be when mounted measured 93.95MM or 3.699".


That leaves a interference fit of .35MM or .014".
My solution was to remove material from the Collars that are on the outside of either side of the swing arm.
The book shows that they are 6MM thick.
However, I measured them at 5.95MM or .234" thick.
I precision ground (Bench grinder and a 17MM rod) each to 5.59MM or .220" thick.


Everything fits together nicely.


These Collars are hard anodized so, they may need to be anodized again depending on how fast the ground soft aluminum surface wears.
My next project is to check the swing arm to right engine case clearance through it's full range of travel as I believe it may be a bit too tight and I may have to machine the swing arm a bit to make it fit correctly.
I wouldn't want to bottom out my suspension and crack my right engine case

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Found a nice crack in my clutch cover...
Time to go see Mr. Tig


What I'm doing next is checking the clearance between the right engine case and the swing arm.
I have the frame, swing arm, and engine bolted together without the shock so I can test the full range of motion of the swing arm.
To temporarily hold it in the correct position I am using a piece of .154" or 3.91MM steel that fits in between the cylinder and the frame.



I may have to adjust it a bit later but this is fairly close for now.
As you can see by the next photo, it is a tight fit with the swing arm in it's neutral position.

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That part of the swing arm actually has a raised embossed area that is making it a close fit.
I believe I can machine the swing arm about .015" deep by about .25" wide and it will be fine.
I may also have to machine a bit of the clutch cover as shown below.



I am holding off on that until I see how well the swing arm mod works.
The last thing I want to do is make the mating surfaces between the clutch cover and the right engine case any narrower.

With the swing arm all the way in the up position you can see that it already has enough clearance.

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This is what happens on a four year old MX bike that has not had the bearings lubricated.



I was going to replace them anyway but I figured I'd show those non believers what happens with even relatively new bikes if you don't maintain them.

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Here you can see the raised part of the swing arm that is preventing the clutch cover from bolting on.



Just a minute or two with a hand grinder and sander.



As you can see, this easily creates the clearance needed.

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The clutch cover fits perfectly without machining it.
Grinding the swing arm was all that was required.







Note that the water outlet on the right side of the cylinder is currently in the way of the pipe.
I bought a hose kit from Service Honda and turned the outlet facing up.
Now there is just enough clearance.
I also bought the pipe and a arrestor from Service Honda.

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My next step was figuring out how to mount the lower frame rails to the lower frame.
Keep in mind that I am not a metal worker
This is where I was at:



Both sides had the frame rails cut but I needed to remove the inner frame rails from the outer part of the frame.
So, I slowly removed the welds until I could see the crack that is between the inner frame rails from the outer part of the frame



It only took a few minutes and they were out.
Now I am ready to tune up the rails and they will slip in nicely.



Since I do not have many fabrication tools I used the following:



It was inexpensive and easy to use.