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Thread: Atc300x aka 300ex in 350x

  1. #1
    Join Date
    Jul 2005
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    Manheim, PA
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    5,302

    Atc300x aka 300ex in 350x

    Here's my 300x.

    Years ago I was told yeah 250x 300ex motors swap right in. Never saw one in real life or on a forum however. Since I hate job I needed to get my mind off things.

    300x project started

    YES a trx250x / 300ex motor a FITS in.
    NO a trx250x / 300ex motor does NOT bolt in.

    The front lower 350x motor mounts and rear lower mounts line up and bolt in 100%

    The head stay mounts are not used.

    The middle lower bolt between frame rails lines up and bolts in however different width spacers are needed.

    The rear upper motor mount lines up but does not bolt in. You need an extra 20mm on that bolt. 350x is 140mm so you need 160mm long bolt. Belmetric or McMaster-Carr have longer bolts.

    The rear motor mount that bolts onto the frame needs to be formed opposite (mirrored) of the 350x oem mount. The oem length spacer needs to be made longer.

    You could mill half the 300ex rear mount off on opposite side of motor just as guys did on 350xs. But that is not the correct way of doing it. Just make a new mount or you will crack cases. Any metal forming / laser cutting place can do this for you.

    I have the specs to produce the correct spacers for the swap.

    Lastly here is the start of my seat latch base. The sheet metal was junk. Most of them will be by now. I had laser cut this piece to oem specs. However between 3 frames not one had the same dimensions. The old frames were just build +/- 1/16" at least it seems.

    If doing this swap please fully gusset your frames, if you think nearly 40 year old paper think frames are strong I'd suggest not attempting this type of build.

    Stay tuned. This should help people put.
    Attached Thumbnails Attached Thumbnails 20210429_224342.jpg   20210429_224322.jpg   20210429_224315.jpg   20210428_174429.jpg  
    Last edited by oldskool83; 05-06-2021 at 08:59 PM.

  2. #2
    Join Date
    Jul 2009
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    South Florida
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    6,397
    Nice job Aaron , 300ex parts are cheap and easily found .
    78 atc 90/180cc Dickson Full Suspension
    76 ATC90/180cc Nicholson
    77 atc 90 Dickson Full Suspension
    84 KLT 110/123cc Powroll Racer from 80s
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    84 atc 200x Powroll My race bike from 80's
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  3. #3
    jasong_10's Avatar
    jasong_10 is offline At The Back Of The Pack Arm chair racerAt the back of the pack
    Join Date
    Apr 2020
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    Croghan, New York
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    376
    Thanks Aaron, this is great info.
    Jason

    85 ATC 250R - restored stock other than 18" rears, nerf bars, Honda key switch, 14T front sprocket, and white tank and plastics (except rad shrouds)

    87 ATC 200X - restored stock other than 18" rears and nerf bars

    84 TRX 200 - rough but complete budget restore for wife and eventually daughters to bum around on

    Eton Viper 50cc - oldest daughter's current ride

  4. #4
    Join Date
    Jul 2010
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    Thanks for making the thread. I'll keep notes.
    The story of three wheels and a man...

  5. #5
    Join Date
    Jul 2005
    Location
    Manheim, PA
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    5,302
    Cleaned up clarke tank, converted to yamaha atv petcock. Just sealed nicer than old clarke style.
    Attached Thumbnails Attached Thumbnails 20210503_210339.jpg  

  6. #6
    Join Date
    Jul 2005
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    Manheim, PA
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    Built the front hub tonight.
    Attached Thumbnails Attached Thumbnails 20210504_194644.jpg  
    Last edited by oldskool83; 05-04-2021 at 08:50 PM.

  7. #7
    BarnBoy is offline Just Too Addicted Arm chair racerJust too addicted
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    I like it. Keep it coming....
    1984 HONDA ATC200M - OG, mid-restoration
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  8. #8
    Join Date
    Jul 2005
    Location
    Manheim, PA
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    Spacers made & longer bolt came in.

    Motor fits & bolts in 100% now. Attached are my drawings you need to produce the spacers for the swap. OD / ID of spacer is not very critical.

    I used:

    1" OD for rear mount with .425" ID
    7/8" OD for the front lowers with .425" ID

    OD means outside diameter
    ID means inside diameter

    Next will be to line chain perfectly for conversion sprocket hub spacer. There are more cool detailed things to come.
    Attached Thumbnails Attached Thumbnails spacers.jpg   frame.jpg   rear.jpg   fits.jpg  
    Last edited by oldskool83; 05-06-2021 at 08:55 PM.

  9. #9
    Join Date
    Jul 2005
    Location
    Manheim, PA
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    Front hub and caliper rebuilt
    Attached Thumbnails Attached Thumbnails 20210506_221039.jpg  

  10. #10
    Join Date
    Jul 2005
    Location
    Manheim, PA
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    I chose not to use the 350x oil cooler & guard.

    Two reasons:

    #1 - 300ex spark plug coil fits in perfectly at the bottom of the guard mount.

    #2 my cooler did not seem to fit nice on OEM mounts, figured something was tweaked.

    All other mounts will be shaved off but lower guard mount. I had a laser cut piece made to copy the 300ex sheet metal mount. It connects to the head just as it would in a 300ex frame.

    Engineering takes the most time. Being picky helps things fit as Honda designed it. So far it's not a hard swap. The wiring harness might be the worst part. I'm at that point shortly.

    At the same time there is a 300ex build going for my daughter too one day.
    Last edited by oldskool83; 05-19-2021 at 03:16 PM.

  11. #11
    Join Date
    Jul 2005
    Location
    Manheim, PA
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    5,302
    Axle came today. It's width assembled was 43.5" which is .40" narrower then the stock width 350x width at 43.9" thinking of installing a small wheel spacer on the rear or maybe trying tusk extended hubs. Little more mock up is needed until I decide.

    So there it is...300ex axle in 350x.

    Will check chain alignment once the coil mount it welded to the frame which will be finished by end of this week.
    Attached Thumbnails Attached Thumbnails 20210517_172936.jpg   20210517_173549.jpg   20210517_174840.jpg  
    Last edited by oldskool83; 05-19-2021 at 03:19 PM.

  12. #12
    Join Date
    Jul 2005
    Location
    Manheim, PA
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    5,302
    Finished up some small assemblies. My loft is stashed with parts in process. These pins came from forum member I've personal met multiple times. I bought about 7 atv/atc's off him this past winter. The front fender got new OEM rubbers and collars. Tonight I hope to shave everything off the frame which is not needed at this point.
    Attached Thumbnails Attached Thumbnails PINS.jpg   SET.jpg  
    Last edited by oldskool83; 05-19-2021 at 03:20 PM.

  13. #13
    Join Date
    Jul 2005
    Location
    Manheim, PA
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    More. Electronics positioned and will be welded in place tonight with photos.

    Heres the coil holder. This cost me $1.45 to be laser cut. It's very cheap, I sub everything out now than have it milled. Anyone can use the attached drawing if doing the the same swap.

    Louis came thru again with new front axle and spacers.
    Attached Thumbnails Attached Thumbnails 20210509_155259.jpg   received_456546498974814.jpeg  
    Last edited by oldskool83; 05-20-2021 at 08:24 AM.

  14. #14
    Join Date
    Jul 2005
    Location
    Manheim, PA
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    5,302
    Coil mount per my drawing.

    Coil mount welded in location to coil wire does not hit head at all.

    CDI mounted, used 300ex mount but cut it up. Needed to weld a .750" OD x .500 thick boss on frame. It had a M6x1.0 threaded thru hole in it.

    Lastly I need to have a laser cut connector holder made. I did not have an extra frame to cut that off. Everything clears nice so far.
    Attached Thumbnails Attached Thumbnails 1.jpeg   2.jpeg   3.jpeg   4.jpeg   5.jpeg  

  15. #15
    Join Date
    Jul 2005
    Location
    Manheim, PA
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    5,302
    Spend 2 hours messing with wiring routing. PITA - After all that time still need to see if the shock fits in. I needed to take photos so I remember a few months from now when it goes back together. As of now looks like 4 things need put on the frame to hole connectors properly. I have 3 more things to draw up to get made.
    Attached Thumbnails Attached Thumbnails 1.jpeg   2.jpeg   3.jpeg  

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