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Old March 31st, 2010, 04:16 PM   #1
bigblocked
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Question Anyone ever do an engine swap? KX60 into KX80

My daughter has physically outgrown her KX60 but she isn't ready to handle an 80's power. I picked up a 91 KX80 that has a bad engine. I'm going to start tearing both bikes down and put the 60 into the 80 frame. Have any of you done this conversion before? My preliminary measurements tell me that the bottom and front mounts will need to be extended but the swingarm mount will probably be right on. The bottom coolant hose is going to be an issue due to alignment. I'll be swapping all electrical. The connection from the airbox to carb is going to be an obstacle. Anything else?
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Old March 31st, 2010, 04:49 PM   #2
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me and a buddy swapped a trx450r motor into a 400ex frame. Different obstacles but still a swap non the less. The swing arm bolt should go through the case of the engine so the chain maintains close to the same tension or your chain could bind or get real loose when the suspesion cycles. Put that through the engine and line up the sprockets side to side. Then make the rest of the mounts using that as a point of reference.
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Old March 31st, 2010, 04:50 PM   #3
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With a welder, any engine fits any frame.
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Old March 31st, 2010, 04:51 PM   #4
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Old March 31st, 2010, 05:58 PM   #5
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With a welder, any engine fits any frame.
Now that's some useful info.
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Old March 31st, 2010, 06:02 PM   #6
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How about slapping a heavy flywheel weight on the 80, that might smooth out the power delivery enough.
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Old March 31st, 2010, 06:03 PM   #7
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Originally Posted by koochman450r View Post
me and a buddy swapped a trx450r motor into a 400ex frame. Different obstacles but still a swap non the less. The swing arm bolt should go through the case of the engine so the chain maintains close to the same tension or your chain could bind or get real loose when the suspesion cycles. Put that through the engine and line up the sprockets side to side. Then make the rest of the mounts using that as a point of reference.
I'm pretty much on the same page. I took all measurements using the swingarm mount as the base. The sprocket looks like it's going to be off to the side about 1/4" but I dont think that's going to be an issue due to the length of the chain. Thanks for the input.

Next is going to be putting the 80 into the 60 frame. That will take Nuggets approach. Should be a handfull!
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Old March 31st, 2010, 06:05 PM   #8
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How about slapping a heavy flywheel weight on the 80, that might smooth out the power delivery enough.
You think that would be enough to keep it out of the powerband? That sounds like an idea worth trying. Only thing is, I'll need to rebuild the 80. Oh well I'll think it over a couple beers tonight and weigh it out. Thanks for the input
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Old April 1st, 2010, 06:44 PM   #9
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Originally Posted by bigblocked View Post
You think that would be enough to keep it out of the powerband? That sounds like an idea worth trying. Only thing is, I'll need to rebuild the 80. Oh well I'll think it over a couple beers tonight and weigh it out. Thanks for the input
You rebuild that 80, I can show you some tricks to tame it:

1. Timing
2. Jetting
3. Sprockets

ALSO, If you're interested, there may be a way to really make it sweet - but I'm not sure if it works with the 80's - my experience is with the 85's. Basically, you bore out the 85 to the 100 cc bore and use a stock KX100 piston (after a re-chrome). the way the ports are angled, the bigger bore in the 85 cylinder actually retards port timing and makes the 100 a little low and midrange torque monster (as much as you're likely to get out of a 100cc )

Gimmie a pm if you have questions - I love me some two strokes!
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Old April 21st, 2010, 07:42 AM   #10
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the kx and rm 80s have a lot better power spread than the other bikes. thats why you see more kids racing those than the other brands. the hit would not be overwhelming on one of those. and like said above you could add a flywheel to tame it even more. i would go that rout if you have not cut up the motor mounts yet. that or get it together and trade it for a 125 four stroke if you want something tame.
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