2003 KTM 125sx

After losing confidence in the YZ250F reliability due to the valve failure, I listed it on Kijiji for trade for a 2 stroke.  I was offered a 2004 KTM 125sx that was ‘ready to ride’ and when I checked the reviews, this was the year that they sorted out the poor rear suspension.  So I met the guy and my heart sank when I saw the condition of the bike and the huge dent in the expansion chamber but it started ok and sounded alright and for some reason, I went through with the trade.  When I ran the VIN, I found out that it is actually a 2003, great but at least the VIN was not reported stolen.

POS1POS2

When I got it home and started looking closer I found all sorts of little issues, front fender wobbling, play in front wheel bearings and rear shock lower bearing, bent rear sub frame, fork seals leaking, it looks like this poor thing has just been neglected – I would not class this as ready to ride.  It amazes me how people will sell something without even washing it???  Pretty disappointed with the accuracy of the description but I could have walked away and the issues really are relatively minor … so far.  So I got started on fixing it up, here’s a more recent pic,

POS3

Notes

125sx parts list and exploded diagrams

To Do List

  • Adjust power valve?

Completed Tasks

  • Give it a good wash
  • Fix wobble in front mudguard – Front brake cable clamp is missing that provided a spacer, put large washers in for now; new brake cable clamp installed
  • Fix huge cracks in rear mudguard – Used the old tie wrap stitching trick
  • Fix dent in exhaust
  • Remove seat cover – original cover still underneath with only minor tears
  • Bend radiator mount tabs back, prevent them from fouling the forks
  • Threads damaged on oil level check screw – replaced with radiator mount screw since replacement screw had larger (10mm) head
  • Replace worn vent screw in fork cap – not needed, with good screwdriver not much effort is required to undo
  • Check rear brake cylinder, push rod comes out? – looks like it could be normal on parts diagram but the rod is well corroded
  • Replace front wheel bearings
  • Replace rear shock lower mount bearing – replaced with MSR bearing, not teflon
  • Fix seized rebound adjust screw on rear shock – got a 2007 XC-W shock PN 12178C04 mono compression control
  • Fix spring on kick-start shaft – ratchet gear was mis-aligned on shaft – rectified
  • Replace fork seals – refilled with AMSOIL SAE 5 synthetic
  • Thread in left side fork protector mount hole damaged – one or two threads seem ok, new screw held in with thread lock
  • Install new piston – plenty of blow-by on piston skirt, got Wossner piston and ring (awesome!) and new small end bearing
  • Cylinder stud broken, the nut and top of stud were glued in place!!! WTF?!?! – got the old one out with stud remover, installed new
  • Screw and bucket holding the rubber chain guard on the swing arm missing – threads in hole on swing arm trashed, aluminum is thin on swing arm not much there to hold heli-coil, tried tapping to M6 and thread locking, not overly happy with it though
  • Ball bearing for kick start – thanks Dan and TSR
  • New right side drain plug M10x1 – threads in clutch cover are trashed!  There is a bit of the old threads left but the drain bolt slips straight in, tried installing an M10x1.5 Fix-A-Thred insert in the remaining threads but the hole was too small.  Plugged with high heat JB Weld
  • Threads in oil level check screw are trashed – repaired with Fix-A-Thred repair kit
  • Fix broken arm on sub frame – Josh welded it up in auto class.  Update: the weld failed so a small steel bar was fashioned and inserted.  Thought about filling around the bar with JB Weld or drilling holes and holding in place with screws but the bar was a tight fit and there should not be any load trying to pull it out the back of the bike so I think it’s good now
  • Spring for rear brake lever is missing – bought new one
  • Clutch basket and inner hub are both damaged – replaced with used parts found on ebay
  • Clutch holding tool required – used impact driver
  • Replace spark plug – ordered from Fortnine
  • Install new clutch actuator gasket, screw and banjo washer – screw was too long?? had to cut one down
  • Get mineral oil for clutch, top up and bleed clutch actuator – also bled the front brake again
  • Little play in rear wheel – replace bearings, ordered from Fortnine with grips
  • Installed new grips
  • Set race sag and suspension settings to stock – race sag = 105mm, static sag = 30mm, compression damping on rear shock = stock + 1 click
  • Clean rear rim
  • Install new Shinko rear that came with the bike
  • Adjust chain tension
  • Loctite the handlebar perch mount screws
  • New front tire – picked up a very lightly used Dunlop Geomax

SXsubframe

Getting there

One thought on “2003 KTM 125sx

  1. MTOAdmin Post author

    Well apart from the missing knobbies on the front tire and the forks weeping a tiny bit of oil and still feeling a bit sticky, I think it’s finally ready to go!! Fired her up and she sounds wicked.

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