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New to KTM, back from hiatus

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Hey guys! Just recently picked up a 2004 125SX, first KTM or 2 stroke I've ever owned. Took it to the track today and had a blast. It's been about 4 years since I've been on a track so it was a little rough getting back into the swing of things but a lot of the rust shook off by the 3rd moto.

 

Just had a few questions for you guys. The bike looked to be in pretty decent shape when I bought it, all stock, pretty clean other than a few dents in the pipe, had top end done about 4 hrs ago. Went over some things on Saturday (fluids/fasteners/suspension/carb). When I drained the oil it was greyish and then at the track today while I was riding I noticed a whining noise when I got on the gas hard. During the 3rd moto it turned into a grinding noise, only when accelerating hard, so I putted around the rest of the track and pulled off. Any ideas of what could be going on?

 

Also the other question I had is now that I have a KTM, will other riders on orange bikes pull over and get out of my way? (Easy I'm a Dungey fan)

 

 

 

 

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I hear they cry "cheap shot" when bumped in the corners
Your sound could be clutch related or worse.
What's the oil look like now after your maiden voyage?

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Okay so just drained the oil (couldn't get the bike started to warm it up). Alot of metal shavings on the drain plug and oil still has that grey tint. Pulled the clutch plates out and they're okay I guess? I'm not really entirely sure what a bad clutch looks like. I'm thinking of pulling the engine and tearing it down, which I've never done before, just to check everything out. If it's not the clutch it would be something transmission related right?

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Okay so just drained the oil (couldn't get the bike started to warm it up). Alot of metal shavings on the drain plug and oil still has that grey tint. Pulled the clutch plates out and they're okay I guess? I'm not really entirely sure what a bad clutch looks like. I'm thinking of pulling the engine and tearing it down, which I've never done before, just to check everything out. If it's not the clutch it would be something transmission related right?

Metal on the magnetic drain plug is never good.
Definitely time to break it open and see what let go.
Sounds like some tranny bearings.
Bike that old you might want to look at cost to fix vs parting it out/selling and buying something else.
If you open it up you might as well do a full rebuild, crank, rod, piston, rings, all bearings and have cylinder re-plated.
Could be more than the bikes worth and you'll definitely never get your money back after repaired.

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Metal on the magnetic drain plug is never good.
Definitely time to break it open and see what let go.
Sounds like some tranny bearings.
Bike that old you might want to look at cost to fix vs parting it out/selling and buying something else.
If you open it up you might as well do a full rebuild, crank, rod, piston, rings, all bearings and have cylinder re-plated.
Could be more than the bikes worth and you'll definitely never get your money back after repaired.

I'm not really too concerned about cost to repair things, I didn't pay that much for it in the first place and I've always wanted to rebuild an engine so this gives me a chance to learn/build it the way I want it. Plus that way I know everythings good to go. I'm not really too bummed about it in the end. Thank you for the help!
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Can anybody answer a question for me? So I bought a used cylinder, same part number as the one currently on it but the one I just bought doesn't have the large groove for the rubber o-ring that goes between the head and barrel (pic attached of the one I just picked up and a pic of what the other one looks like). Anyone know what's up with this? Was there a revision or something but kept the same part number? thanks in advance!IMG_20170608_212341.jpg.f591b863fe7126d8bcf61632d52c0adb.jpg50330005300-cylinder-ktm-exc-sx-125-01-05-.jpg.c18b70c6acbc612e358e449a97df7b58.jpg

 

 

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Can anybody answer a question for me? So I bought a used cylinder, same part number as the one currently on it but the one I just bought doesn't have the large groove for the rubber o-ring that goes between the head and barrel (pic attached of the one I just picked up and a pic of what the other one looks like). Anyone know what's up with this? Was there a revision or something but kept the same part number? thanks in advance!IMG_20170608_212341.jpg.f591b863fe7126d8bcf61632d52c0adb.jpg50330005300-cylinder-ktm-exc-sx-125-01-05-.jpg.c18b70c6acbc612e358e449a97df7b58.jpg
 
 

I did a little fishing and it looks like you have a 2001 or early cylinder.
They switched to the o-ring design in 2002 from what I can tell.
IMG_4901.PNG
IMG_4902.PNG
Not sure why the part numbers would be the same. They aren't on Rocky Mountain ATV.
IMG_4903.PNG
IMG_4904.PNG
You buy it on EBay?
Hopefully you can get your money back.
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Yeah I had checked earlier years and noticed that as well, but the number on the side of the barrel definitely says 50330005300. I did get it off of eBay, was off an 03 125sx. If there's no difference fitment/performance wise between the two other than the o-ring I'd like to use it, just wanted to see if maybe there was something I'm missing.

 

 

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Hi, KTM used the same crankcases from 1998 to 2012 so your cylinder will fit. Not sure which one you've bought? The newer looking one was used between 2003 and 2006 and uses 2 o rings, the outer one having a bobble on it to cover the flap lifter bolt hole. The older looking one was used between 1998  and 2002 and uses the inner o ring and a fibre outer gasket. Your pv assembly is interchangeable between both. What condition is the cylinder you've bought compared to the one on the bike? Every used 125sx ever sold in the world has had a " new top end few hours ago".  This is usually not the truth!! It would be worth your while whipping the cylinder off and having a check. The cylinders are nikasil plated  - hold it up to the light and check for dullness, like matt grey above the exhaust port where it wears first. Also see if you can catch a ridge with your fingernail where the top ring stops at tdc. Do the same with your newly acquired cylinder. Either will dictate a replate.  Also be wary of the exhaust port bridge are they are bad for chipping (then catch a ring) on the early cylinders. The front left cylinder nut is difficult to remove and you will have to grind down a 12mm ring spanner to get it on. Don't be tempted to use an open ender as you will round the nut. Motion Pro make a torque convertor spanner which fits perfectly. Workshops manuals are readily available on the internet for free - they are easy engines to work on. Hope this helps. Bob.

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Upon inspecting the two side by side, my original is slightly taller, maybe 1/16th of an inch, and stamped 'Elko 1', while the new one is stamped 'Elko 2'. Also on the bottom there's a groove leading into the power valve that's slightly shallower on the one I just purchased. Its just blowing my mind that there are these few pretty significant differences but still has the same part number.1496962283946.jpeg1496962325596.jpeg1496962354750.jpeg1496962392544.jpeg1496962423101.jpeg

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Hi, KTM used the same crankcases from 1998 to 2012 so your cylinder will fit. Not sure which one you've bought? The newer looking one was used between 2003 and 2006 and uses 2 o rings, the outer one having a bobble on it to cover the flap lifter bolt hole. The older looking one was used between 1998  and 2002 and uses the inner o ring and a fibre outer gasket. Your pv assembly is interchangeable between both. What condition is the cylinder you've bought compared to the one on the bike? Every used 125sx ever sold in the world has had a " new top end few hours ago".  This is usually not the truth!! It would be worth your while whipping the cylinder off and having a check. The cylinders are nikasil plated  - hold it up to the light and check for dullness, like matt grey above the exhaust port where it wears first. Also see if you can catch a ridge with your fingernail where the top ring stops at tdc. Do the same with your newly acquired cylinder. Either will dictate a replate.  Also be wary of the exhaust port bridge are they are bad for chipping (then catch a ring) on the early cylinders. The front left cylinder nut is difficult to remove and you will have to grind down a 12mm ring spanner to get it on. Don't be tempted to use an open ender as you will round the nut. Motion Pro make a torque convertor spanner which fits perfectly. Workshops manuals are readily available on the internet for free - they are easy engines to work on. Hope this helps. Bob.

Great info.
So if it's refurbished all you'd need is a fiber head gasket and she's good to go.

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Yes, although a fresh top end may not address other issues. Personally I would use the later (refurbed) cylinder and keep the other as a spare. Remember you have to set the deck height, think yours will be 0.00 but check, on KTM 2 strokes. If you've not changed over the pv assembly between cylinders, follow your manual or come back. Tools needed are 6 and 8mm sockets, 2 x 0.20mm feeler gauges - you use 2 at the same time to centre the flap - and a 6mm bolt to lift out the (threaded) pv lifter rod.

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Hi, KTM used the same crankcases from 1998 to 2012 so your cylinder will fit. Not sure which one you've bought? The newer looking one was used between 2003 and 2006 and uses 2 o rings, the outer one having a bobble on it to cover the flap lifter bolt hole. The older looking one was used between 1998  and 2002 and uses the inner o ring and a fibre outer gasket. Your pv assembly is interchangeable between both. What condition is the cylinder you've bought compared to the one on the bike? Every used 125sx ever sold in the world has had a " new top end few hours ago".  This is usually not the truth!! It would be worth your while whipping the cylinder off and having a check. The cylinders are nikasil plated  - hold it up to the light and check for dullness, like matt grey above the exhaust port where it wears first. Also see if you can catch a ridge with your fingernail where the top ring stops at tdc. Do the same with your newly acquired cylinder. Either will dictate a replate.  Also be wary of the exhaust port bridge are they are bad for chipping (then catch a ring) on the early cylinders. The front left cylinder nut is difficult to remove and you will have to grind down a 12mm ring spanner to get it on. Don't be tempted to use an open ender as you will round the nut. Motion Pro make a torque convertor spanner which fits perfectly. Workshops manuals are readily available on the internet for free - they are easy engines to work on. Hope this helps. Bob.

Thanks for the info! I have the engine completely torn apart because a transmission bearing let loose shortly after I purchased the bike and caused some damage to the case. Decided the case is still usable but didn't really come to the conclusion until after I purchase a new set of cases so I've decided to put a spare engine together. The original cylinder had some light gouging on the skirt and plating was worn around the PV. Same goes with the one I purchased but I got it for a decent price and planned to have them both replated. So even though the part #s match you're saying I bought the old style? I've looked through the manual and it says from 02 onwards the o-ring was used instead of the gasket. Its just confusing since 98-12 will fit, but from researching the OEM fiche each time the style changed so did the part #. If I use the slightly shorter one will piston clearance with the head be an issue? Or is that solved with the fiber gasket that is used?

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Hi, just had another thought while I was trying to sleep. The real early KTM cylinders which take the fibre gasket were a slightly bigger bore but look totally the same as the later fibre gasket ones. You will HAVE to get the cylinder measured to make sure it is a 54mm bore ie 2001 or younger. I wouldn't think you will have anything like the necessary measuring equipment to accurately achieve this so will have to go to a shop. The early cylinders took a 54.25 piston as opposed to (your) 53.94/95 piston. It's a bit complicated as 1998/1999/2000/2001/02/03 saw a lot of changes to the 125 motor.  Bob.

Edited by 7Tktm

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Hi, just had another thought while I was trying to sleep. The real early KTM cylinders which take the fibre gasket were a slightly bigger bore but look totally the same as the later fibre gasket ones. You will HAVE to get the cylinder measured to make sure it is a 54mm bore ie 2001 or younger. I wouldn't think you will have anything like the necessary measuring equipment to accurately achieve this so will have to go to a shop. The early cylinders took a 54.25 piston as opposed to (your) 53.94/95 piston. It's a bit complicated as 1998/1999/2000/2001/02/03 saw a lot of changes to the 125 motor.  Bob.

I appreciate the help, I actually work in a machine shop so I'll bring it into work tonight and measure the bore and see if I can get to the bottom of this

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Measured the bore, sitting at about 54.285mm...that being said, the way it measures it should be a 2000 or later...but the part number doesn't match those years. I'd really like to know what I've got here lol

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Hi, would suggest you have a pre 2000 cylinder which has a 54.25 bore as opposed to a 54.00 bore of the later cylinders so it won't do your bike. You could fit it but would have to use the 1998 - 2000 crank, con rod and piston as well. The casings are the same though. Lot of hassle and as said you would be better using the cylinder which came with the bike if it's the one that takes the 2 o rings. Not hindsight, but I would never buy a replacement cylinder from ebay or similar unless it had been freshly plated and not used. People tend to unload their junk on such sites. I never for a moment though it would be a pre 2000, jeepers that's 17 years old. Bob.

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