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Thread: Xr500 Topend bolting onto 350x

  1. #1
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    Exclamation Xr500 Topend bolting onto 350x

    I remeber reading that a complete xr/xl 500 top end bolts on to the 350x bottom end. Is this true? If so i think im gonna be building me a 500x sometime soon?
    Or was i realllly tired when i thought i saw this ?
    Thanks! Cragster
    '86 200x

  2. #2
    mean350 is offline Just Too Addicted Arm chair racerJust too addicted
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    dont know if it works but that would be awesome!!!

  3. #3
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    yeah thats what i was thinkin! i coulda swore i read it though....
    '86 200x

  4. #4
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    Quote Originally Posted by cragster
    I remeber reading that a complete xr/xl 500 top end bolts on to the 350x bottom end. Is this true?
    Or was i realllly tired when i thought i saw this ?
    Yes,you were really tired.
    85/86 ATC 567x






    Bailey(11/30/97-4/17/06) My little angel

  5. #5
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    You think so? So theres no way this will work?
    WHat about a 400ex/450r/crf450 etc etc?
    Im for real i swear i read it
    '86 200x

  6. #6
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    Quote Originally Posted by cragster
    You think so? So theres no way this will work?
    WHat about a 400ex/450r/crf450 etc etc?
    Im for real i swear i read it
    Give me a minute or 2,gonna send a pm
    85/86 ATC 567x






    Bailey(11/30/97-4/17/06) My little angel

  7. #7
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    i read on another form it would work but only a couple of years. and the cases had to be modified. it also said that the gain wasnt worth the trouble. it stated that the big bore kit made alot more power.

  8. #8
    Billy Golightly's Avatar
    Billy Golightly is offline Always finding new and exciting ways to not give a hoot in hell Catch me if you can
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    It doesnt bolt up, I dismissed this myth a long long time ago. With extensive center case welding and machining yes it might be possible. The heads however do for the most part seem to bolt right in place of each other. THe difference being the rocker cover with the top head stay mount for the XR500 engine is near the front of the engine insteead of the back. It hits and rubs on that backbone of the frame where the airbox tube hooks to. More trouble then its worth IMO

  9. #9
    leprogle's Avatar
    leprogle is offline At The Back Of The Pack Arm chair racerAt the back of the pack
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    I was told that the xr 500 headpipe mounts up, however and is BIGGER. and everyone knows bigger is better. He said it made it work a hell of a lot better
    Caution
    Do not "POP WHEELIES" and run for any distance with the ATC. The oil capacity is relatively small and the oil will drain out of the oil pump area thus causing loss of oil pressure, resulting in costly engine damage -CLYMER

  10. #10
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    what about just swaping the 500XR engine for the 350X engine. Would it be a pretty easy swap?

  11. #11
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    I had 1 of these xr500 conversions it was a cobbled mess with all the frame mods it takes too make the 500 fit
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  12. #12
    nate b is offline At The Back Of The Pack Arm chair racerAt the back of the pack
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    i remember reading about that in dirtwheels or something. They did a 500 big bore 350x and It seemed like it was a bolt on mod? of course that was probably 15 years ago when I read that.
    85 atc 250r;
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  13. #13
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    hi i dont know how -because of the cam timing!!! the cam sprockets the same?
    maby your camsproket if cylinder fits

  14. #14
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    its not worth the hassle, a bore kit and cam will get you more power. the only advantage is the 500 head has bigger valves and ports, but thats only an advantage on a bigger cc motor. the top end is oiled internally on the 500 and you have to do some drilling in the 350 cases to make it work. put in a 452 bore kit, cam, and fcr carb and you'll have plenty of power for a 350x.

  15. #15
    mean350 is offline Just Too Addicted Arm chair racerJust too addicted
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    where do *Edited* get a 452 bore kit, cam, and fcr carb at anyways?

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