1991 KTM 125 MX Rebuild / Resto
Posted: Tue Mar 06, 2012 12:02 pm
I just picked up my first bike. A couple guys at work ride and have been pestering me to join them out on the trails, so I got looking for a bike. I stumbled on this partially disassembled, but otherwise complete and pretty solid '91 125MX on Craigslist.
Came with a clean & clear title, and current green sticker (can ride year round in public OHV areas) good through middle of next year.
I paid $350 for it, even with all the work it needs I think I got a good deal.
It came with the engine in a box in pieces - side covers loose, flywheel nut loose, but was advertised as having the bottom end already rebuilt at the Malcolm Smith dealership outside LA.
But... the rebuild was about 6 years ago. It has fresh bearings and a new connecting rod, but never had the cylinder put back on. Came with a pretty detonation eroded piston with one skirt broken, and lots of things carboned up. All the water passages are badly corroded, silicone splooged all over the powervalve actuator rod bushing, etc.
Lots of grit down in the crankcase and overall just needs cleaned up.
The bike sat outside for some time, the plastics are all pretty brittle and a little crumbly looking, but otherwise it's in nice shape. Doesn't look like it was layed down too much, has good (but old) tires.
****************************************
Even by KTMTalk standards this bike is appearing more and more unusual, and I've been struggling to find service info.
Lots of threads on this generation 250's and 300's, but not much on the 502.xx engined 125's. Gasket kits appear to be almost identical to the 503.xx engined bikes that ran '93-'97 and photos of pistons and things appear to be the same, hope to find some interchange info there as well.
***************************************
I ordered a factory service manual on CD and am waiting for it to come in, but for now my checklist roughly includes:
-Disassemble & clean engine, then re-assemble case
-Ultrasonic clean all case & water cooling parts to break up corrosion
-Weld broken radiator hose spout back together
-Make insert for broken bolt riser in clutch basket (one is sheared clean off, only 4 out of 5 bolts were in the clutch)
-Reassemble top end with new NOS Wiseco piston kit, scuff up Nikasil cylinder liner that appears in decent shape
-Rebuild carb, ultrasonic clean all the parts (Delorto 37 VHSB-FD)
-Adjust powervalve linkage (old mechanical RPM governor gear driven by clutch basket)
-Set ignition timing (SEM ignition system, no lighting outputs from generator)
-Rebuild front brake master cylinder - plastic sight glass crumbled away, cylinder sat dry and seals probably shot
-Un-stick rear caliper - rear brake lever has pressure, but pads don't move in the caliper, hopefully piston just seized up a little and can be lubricated
-Make new slide pin for shifter ratchet
-Replace missing spring return for kick starter
Came with a clean & clear title, and current green sticker (can ride year round in public OHV areas) good through middle of next year.
I paid $350 for it, even with all the work it needs I think I got a good deal.
It came with the engine in a box in pieces - side covers loose, flywheel nut loose, but was advertised as having the bottom end already rebuilt at the Malcolm Smith dealership outside LA.
But... the rebuild was about 6 years ago. It has fresh bearings and a new connecting rod, but never had the cylinder put back on. Came with a pretty detonation eroded piston with one skirt broken, and lots of things carboned up. All the water passages are badly corroded, silicone splooged all over the powervalve actuator rod bushing, etc.
Lots of grit down in the crankcase and overall just needs cleaned up.
The bike sat outside for some time, the plastics are all pretty brittle and a little crumbly looking, but otherwise it's in nice shape. Doesn't look like it was layed down too much, has good (but old) tires.
****************************************
Even by KTMTalk standards this bike is appearing more and more unusual, and I've been struggling to find service info.
Lots of threads on this generation 250's and 300's, but not much on the 502.xx engined 125's. Gasket kits appear to be almost identical to the 503.xx engined bikes that ran '93-'97 and photos of pistons and things appear to be the same, hope to find some interchange info there as well.
***************************************
I ordered a factory service manual on CD and am waiting for it to come in, but for now my checklist roughly includes:
-Disassemble & clean engine, then re-assemble case
-Ultrasonic clean all case & water cooling parts to break up corrosion
-Weld broken radiator hose spout back together
-Make insert for broken bolt riser in clutch basket (one is sheared clean off, only 4 out of 5 bolts were in the clutch)
-Reassemble top end with new NOS Wiseco piston kit, scuff up Nikasil cylinder liner that appears in decent shape
-Rebuild carb, ultrasonic clean all the parts (Delorto 37 VHSB-FD)
-Adjust powervalve linkage (old mechanical RPM governor gear driven by clutch basket)
-Set ignition timing (SEM ignition system, no lighting outputs from generator)
-Rebuild front brake master cylinder - plastic sight glass crumbled away, cylinder sat dry and seals probably shot
-Un-stick rear caliper - rear brake lever has pressure, but pads don't move in the caliper, hopefully piston just seized up a little and can be lubricated
-Make new slide pin for shifter ratchet
-Replace missing spring return for kick starter