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Thread: XR50 2003 50cc Modified

  1. #1
    Forum Founder Classic Honda 50's's Avatar
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    XR50 2003 50cc Modified

    Picked up the XR50 a few years ago for just over $700 off EBay with only a quick 5 hour return trip for this one, started first kick and went thru the gears ok but had a bit of a leak from the sump plug and the head had been replaced with a China head but it ran ok and was basically good to go:

    2002 XR50 Pic 3 S.jpg


    Off home for a bit of TLC but just as it rolled into the shed it just fell apart, Nichole has seen this happen many times before :

    DSC03276.jpg


    I had a very tidy CRF50 roller that donated it's rear swingarm and forks with heavy duty springs and bushes, replaced the original plastics with the old plastics from my other XR50 and installed an almost new CRF50 head, barrel and carb that I also picked up off EBay:

    DSC03271.jpg

    DSC03277.jpg

    DSC03279.jpg


    Safe and reliable for my kids to ride for now
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    PERFORMANCE, REPRODUCTION AND OEM PARTS TO SUIT OLD AND NEW HONDA AND OTHER 4 STROKE MINIBIKES AND MOTORBIKES INCLUDING KAWASAKI, YAMAHA AND SUZUKI.

    Parts to Suit: Honda Z50A, Z50J1, Z50JZ, Z50R, Z50JDM, Z50M, QA50, QR50, MR50, XR50, CRF50, ATC70, CT70, CZ100, MSX125 (Grom), ST70, SL70, XL70, TRX70, XR75, XR80, TRX90, Kawasaki KLX110 and Z125 models to name a few.

  2. #2
    Forum Founder Classic Honda 50's's Avatar
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    I absolutely hate oil leaks and I soon worked out that the sump plug had been stripped and the thread had been poorly repaired resulting in a cracked engine case and the gearshift shaft was bent pretty bad as well so I removed the original engine and replaced it with a spare CRF50 TB V2 108cc stroker engine that I had till I was able to repair the original motor:

    DSC05289.jpg


    Just had to machine up a few fuel tank spacers for carburettor clearance and it fit like a glove, ready for some adult fun as the kids were now too scared to ride it:

    DSC04124.jpg


    Can never stop at one bike they seem to breed when you put them near other bikes :

    Dsc05290S.jpg

    Dsc05293S.jpg
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    Parts to Suit: Honda Z50A, Z50J1, Z50JZ, Z50R, Z50JDM, Z50M, QA50, QR50, MR50, XR50, CRF50, ATC70, CT70, CZ100, MSX125 (Grom), ST70, SL70, XL70, TRX70, XR75, XR80, TRX90, Kawasaki KLX110 and Z125 models to name a few.

  3. #3
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    Was told that the bike had been raced for two years by the first owner and all of the new owners kids had learn't to ride on it and there were kids everywhere so I did not expect to see the bottom end in very good condition but I was surprised to see that it was one of the cleanest motors internally that I had ever seen, I like farm bikes as farmers tend to look after and service their equipment:

    Dsc03274 S.jpg

    Dsc03275 S.jpg


    The gearshift lever was a little bent although it was still working ok and surprisingly didn't leak at all:

    Dsc07006 S.jpg


    Then the motor was put away in the project waiting room for almost two years till I got around to rebuilding the stock motor
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    Parts to Suit: Honda Z50A, Z50J1, Z50JZ, Z50R, Z50JDM, Z50M, QA50, QR50, MR50, XR50, CRF50, ATC70, CT70, CZ100, MSX125 (Grom), ST70, SL70, XL70, TRX70, XR75, XR80, TRX90, Kawasaki KLX110 and Z125 models to name a few.

  4. #4
    Moderator dex's Avatar
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    What exhaust do you have on there ,,?
    its engine oil madge ,,,
    Your soaking in it ,,!!

  5. #5
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    With the stock set-up I just run a modified stock pipe and with the TB 108 I have a Fast 50s 1" exhaust that is a tad loud.
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  6. #6
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    A new centre case solved the stuffed sump plug problem:
    DSC07012.jpg


    Transmission was like new but had a strange pattern on the face of the teeth on the gears, will see how it goes:
    DSC02453.jpg


    Lubed up ready to go back together:
    DSC02456.jpg


    DSC02458.jpg


    DSC02461.jpg


    DSC02465.jpg
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  7. #7
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    Can't leave anything stock so I installed a Kitaco stock head race cam, mild port job, re-cut the valve seats to drop the valves into the head and move the valve seat contact to the outer edge of the valve face and match ported the inlet manifold.

    A modded stock exhaust with an XR/CRF70 carburettor and inlet manifold running a short foam pod air filter tops off the engine set-up.

    The forks already had heavy duty springs so I added a Takegawa rear shock which works well with my 90kg load.

    Tiny inlet port feeding the stock 19mm inlet valve, I take the inlet port out to 16mm:
    DSC02469.jpg


    Exhaust port needs a clean up:
    DSC02470.jpg


    The combustion chamber is quite small and houses a 19mm inlet valve and 16mm exhaust valve:
    DSC02472.jpg


    Stock cam on the left and the Kitaco stock head race cam on the right:
    DSC02473.jpg


    Match the inlet manifold to the inlet port:
    DSC02482.jpg


    DSC02487.jpg


    Match the other end to the carb insulator plate:
    DSC02490.jpg


    Inlet port almost finished:
    DSC02497.jpg


    Exhaust port cleaned up:
    DSC02499.jpg


    Cut new multi angle valve seats:
    DSC02521.jpg
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  8. #8
    Life Member z nut's Avatar
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    is that a crack in the case?
    You have two parts of brain, 'left' and 'right'. In the left side, there's nothing right. In the right side, there's nothing left.

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  10. #9
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    Please no which one, there was lots of weird casting flash.
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  12. #10
    Life Member z nut's Avatar
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    just taking the piss...... Dex taught me that
    You have two parts of brain, 'left' and 'right'. In the left side, there's nothing right. In the right side, there's nothing left.

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  14. #11
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    Clutch side of the engine close to finished:
    DSC02535.jpg


    Flywheel side of the engine ready to close up:
    DSC02536.jpg


    This is the last thing I like to see before the engine is ready to bolt up, oil pump drive sprocket engaged, tensioner roller and guide roller in place and remember the two little O rings that sit behind the stator plate:
    DSC02539.jpg


    Cam sprocket aligned:
    DSC02541.jpg


    Ready for the clutch and head covers, the clutch was in great condition, cleaned out the usual grey paste from under the top cover and just gave the stock plates a figure eight lap on wet and dry paper, cleaned then oiled the plates for assembly:
    DSC02544.jpg


    Helpful tool that you can make to install the oil pump drive shaft to the drive shaft sprocket after the engine is assembled, wont work with some stroker cranks including the TB 51mm crank where you need to install the drive shaft when bolting the centre cases together:
    DSC02547.jpg


    Ready for the flywheel cover and round one with the stock Honda 50 carb:
    Dsc02554 C.jpg
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  15. #12
    Moderator dex's Avatar
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    That big split where the two half's meet ,,?

    Hahhah ..
    its engine oil madge ,,,
    Your soaking in it ,,!!

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  17. #13
    Life Member z nut's Avatar
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    im sorry Jaimie but im still waiting for my free roller rocker head after i hit the 1000 posts mark.
    You have two parts of brain, 'left' and 'right'. In the left side, there's nothing right. In the right side, there's nothing left.

  18. #14
    Forum Founder Classic Honda 50's's Avatar
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    Sorry I have to delete 952 of your posts due to complaints from the Communications Ombudsman.
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  20. #15
    Life Member z nut's Avatar
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    few more than that i recon
    You have two parts of brain, 'left' and 'right'. In the left side, there's nothing right. In the right side, there's nothing left.

  21. #16
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    When I first started the bike I was using an as new OEM CRF50 carb and air filter assembly, the engine started with a few kicks idled and run nice, I like to put a rebuilt engine through 3 heat cycles then retension the head but into the third cycle the engine started to run on when backing off the throttle, went looking and found a few good examples of what can make your bike run rough after it has been sitting around for a while.

    The Honda OEM air filter element was less than two years old as I had replaced it when I first bought the bike home, surprisingly it was quite fragile and disintegrating:
    DSC02561.jpg


    The rubber O ring between the cylinder head and inlet manifold was flat so I replaced it along with the O ring in the insulator spacer and the front face of the carburettor:
    DSC02565.jpg


    Also lubed the throttle cable just in case it was sticking and the engine was running quite well at this stage with the new parts fitted but it felt restricted and needed some more air.

    So I replaced the CRF50 carb with an OEM XR/CRF70 carb and inlet manifold only had to make a small adjustment to the throttle tube for cable slack, the 70 carb makes a lot of difference, will get a video of it running, sounds great with the throaty mid-range/top end roar through the small foam pod air filter:
    DSC02684.jpg


    Stock jetting as it came out the box, have two of these carbs on my bikes it is one of my favourite 50cc engine upgrades:
    DSC02687.jpg


    The inlet manifold flange that bolts to the cylinder has had 6mm shaved off it to provide clearance to the frame from when the carb was on my J1, this frame seems to have more clearance so I will be able to get a heat spacer between the head and manifold.


    The Takegawa rear shock is spot on for me at 90kg, the kids will grow into it :
    DSC02678.jpg
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  22. #17
    Forum Founder Classic Honda 50's's Avatar
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    Finished ready for the track and trails:
    DSC02673.jpg


    DSC02683.jpg
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  24. #18
    Moderator dex's Avatar
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    Bung inch spacer's or a block of shaped aluminium between the motor and peg mounts ,,
    Will open up the peg/seat/bars relationship,,,,and make your original sidestand usable again .
    Remember to readjust your rear brake ..
    With a tall foam set on the seat ,even better .
    its engine oil madge ,,,
    Your soaking in it ,,!!

  25. #19
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    Time for the last engine mod for this XR50 with the addition of a Kitaco forged 12:1 39mm piston kit -

    DSC03533.jpg

    This bike is one of my customer request modified bikes, if someone asks a question on how a part works I try it and find out, best way to get upgrades past your wife

    Cheers

    Jaimie
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  27. #20
    Charter Member Paulie's Avatar
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    Customer requests you say...
    can I please request you do a twin cam? I’d like to learn more about them.

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  29. #21
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    Will add that to the list, I am building a 124 for my JZ with a V2 head and Takegawa piston but would like a Kitaco DOHC set-up to see the difference.

    Finishing my dyno is next on the to do list for a proper side x side comparison.
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    Parts to Suit: Honda Z50A, Z50J1, Z50JZ, Z50R, Z50JDM, Z50M, QA50, QR50, MR50, XR50, CRF50, ATC70, CT70, CZ100, MSX125 (Grom), ST70, SL70, XL70, TRX70, XR75, XR80, TRX90, Kawasaki KLX110 and Z125 models to name a few.

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