BUILDING A KX500AF with a 2007 KX250F chassis

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The head stay made it in today:



Now I can start making all the mounting brackets and get them welded on.

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Any guesses as to what this is for?
If my idea works I'll post details later

block1.JPG (42.61 KiB) Viewed 16022 times

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I'm also working on removable motor mounts.
Most guys weld the motor mounts directly to the frame.
However, using a KX250F frame limits the amount of space you are working with.
So, I will drill through the frame tubes and weld in aluminum tubing.
This will give the strongest mounting points and allow the mounts to be easily removed which will make engine removal a lot easier for future upgrades
It will be a little harder to do but I feel it's worth the effort.

2.jpg (46.13 KiB) Viewed 16022 times

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Here's another pic with a little more details:

engine mounts 2.JPG (18.23 KiB) Viewed 16022 times

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I have the aluminum mount made.

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I had considered a slightly different design but decided in favor of the design above:

mount.JPG (20.79 KiB) Viewed 16021 times

[Sandblaster]

Because a few people had problems breaking their frame rails I wanted to be sure I understood where the transfer of energy was taking place at.
Here is a rough diagram of where the mounting points are in relation to the frame.

frame lay out.JPG (36.63 KiB) Viewed 16015 times

As you can see, when coming down hard on a jump the force is transferred in a radial motion.
So, the rear mounts must be in line as much as possible with the direction of the force.
Further, having the front mount on the head helps to stop any force that is trying to be transferred to the frame rails.
Here is some pics of the different views.
Nothing is welded yet but you get the idea:

K5AF REAR HEAD MOUNTS TOP VIEW.JPG (24.41 KiB) Viewed 16015 times

K5AF REAR HEAD MOUNTS TOP VIEW 2.JPG (82.35 KiB) Viewed 16015 times

K5AF REAR HEAD MOUNTS REAR VIEW.JPG (39.27 KiB) Viewed 16015 times

K5AF REAR HEAD MOUNTS BOTTOM LEFT SIDE.JPG (22.37 KiB) Viewed 16015 times

That's my story and I'm sticking to it for now

[Steve O]

Very nice. I can see why people had problems with the frame rails. By the way, love the cad drawings. Put that degree to work !

[Sandblaster]

Yeah I thought about doing the whole engine in CAD but in reality I just wanted to visualize the problem without all the pieces in the way.
Once that was done it was a lot easier to see why others had trouble.
Their top mounts are hanging down perpendicular to the arc.
In essence they made a big lever that their engine pulls against
I wouldn't do it that way but what do I know...
I guess we'll see when my test pilot gets a little flight time logged

[Sandblaster]

I finally got the engine mounts done.
It's amazing how long this stuff takes when you don't have the proper tools
The front and lower mounts came out exactly as I planned in that they would be exactly the same size as each other.
The top mounts are completely different as you would expect.
Try that when you are cutting out the original carriage that they all mounted too and try to fab and weld something completely new.
Yeah, I got lucky
The only change was on the lower left side of the engine there is a protuberance that requires the mount to be slightly machined for clearance.
It's all good as I was able to make them all the same, drill them, and then machine one of them to fit.

KX500AF ENGINE MOUNTS.JPG (71.7 KiB) Viewed 16011 times