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Discussion Starter #1
Hey, I recently bought used ktm exc 125 2008, it couldn't idle and felt like it had low compression so I opened the top end and saw the cylinder is in bad shape (exhaust port nikasil wore down).
Now wanted to order a new cylinder but saw that the part number is from ktm exc 2002-2005 (while the engine is definitely 2008 from the engine number), and the cylinder head is from 1998-2000
Part number cylinder head 50330006100
Part number cylinder 50330005300
They seems to fit, but I'm not sure if it's fine.
Any tips on which cylinder to buy? If I'll buy the cylinder and head for 2008-2016 will the power valve (including covers) fit?
 

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Send your cylinder off to replate it for better economy. You can verify your cylinder head for its fitment by checking your part numbers in online parts catalog available at MotoSport or RMATV or others. You may find a previous owner switched cylinder head for availability or possibly performance increase. Some XC motors will see a performance increase when substituting SX cylinder head on the XC motors. US Chrome and Millennium can replate your cylinder and offer lifetime warranty on their work.
 

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Send your cylinder off to replate it for better economy. You can verify your cylinder head for its fitment by checking your part numbers in online parts catalog available at MotoSport or RMATV or others. You may find a previous owner switched cylinder head for availability or possibly performance increase. Some XC motors will see a performance increase when substituting SX cylinder head on the XC motors. US Chrome and Millennium can replate your cylinder and offer lifetime warranty on their work.
I don't have a replating service in my country and sending it to replate is the same cost as a new cylinder.
I just want to make sure I buy the right parts and that the power valve will fit properly.
I checked in MotoSport and they have different parts number for the years, but I understood that they may fit.
 

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Not sure of interchangeability on those older ones but some of the newer 125 bikes are getting the 150 cylinders for them with good power boost. I don't work much on those but @Axzon may be able to steer you in the right direction. His team races the small bore bikes
 
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Welcome to the forum!
If you give me the motor number I can help regarding what cylinders and heads will fit. You find the motor number on the left side just under the cylinder. If the motor is the original one in your frame, please also give the frame/VIN# number. (You find the VIN# on the right side of the steering neck)
 

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Discussion Starter #6
Welcome to the forum!
If you give me the motor number I can help regarding what cylinders and heads will fit. You find the motor number on the left side just under the cylinder. If the motor is the original one in your frame, please also give the frame/VIN# number. (You find the VIN# on the right side of the steering neck)
Thank you!
My engine number is 850356999
VIN is VBKGSA2078M112101
 

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Thank you!
My engine number is 850356999
VIN is VBKGSA2078M112101
Thanks. I come back with what I can find out for you. Give me a day or two.
 
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Discussion Starter #8
New info, it seems that power valve of 2008 has a different part number than 2005, which make me think the power valve I currently have wouldn't fit on 2008 cylinder (only the side covers and the control flap are different) . The control flap including the new cylinder head is quite expensive.
Will I be okay in buying a new cylinder with the same part number of what I already have?
Or in other words, will a 2005 full top end fit a 2008 engine (I'm 100% sure they fit, but not sure if they fit properly without hurting the engine)
 

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The 8 at the start of the engine number is for 98 (not 08) in your case. In 08 KTM used the 515 engine for the 125, 144, 150 and 200 engines.
The 503 engine was used from 1997 to 2001 for 125/200
The 512 engine was used from 2000 to 2001 for 125
The 523 engine was used from 2000 to 2002 for 200
The 523 engine was used in 2002 for 125
The 515 engine was used in 2001, 2003 to 2012 for 125/200
The 524 engine was used from 2013 to 2015 for 125/200

The frame/VIN number you have given is for a 2008 bike


So with that info you might have to re-think your approach.
 

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Discussion Starter #10 (Edited)
The 8 at the start of the engine number is for 98 (not 08) in your case. In 08 KTM used the 515 engine for the 125, 144, 150 and 200 engines.
The 503 engine was used from 1997 to 2001 for 125/200
The 512 engine was used from 2000 to 2001 for 125
The 523 engine was used from 2000 to 2002 for 200
The 523 engine was used in 2002 for 125
The 515 engine was used in 2001, 2003 to 2012 for 125/200
The 524 engine was used from 2013 to 2015 for 125/200

The frame/VIN number you have given is for a 2008 bike


So with that info you might have to re-think your approach.
Thank you very much!
But now I'm a bit confused, I saw some engine numbers such as 3-503 and 6-503 (of ktm 125/200) on the web:
That means they are from 2003/6 I think?
In any case, I think the best approach for now is to keep the same cylinder and head numbers which worked until now. Do you this could cause a problem?
If I understand correctly all the 125 engines can fit any top end as the changes aren't major.

Edit: I also saw you wrote that any cylinder with 503 at the beginning will fit, but the cylinder of 2008 is 50330005544, doesn't it mean that they have the same engine?
 

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The 125 cylinders and what years they are used in:
50230005244 1994
50230005244 1995
41905420 1996
41905420 1997
50330005000 1998
50330005000 1999
50330005100 2000
50330005200 2001
50330005300 2002
50330005300 2003
50330005300 2004
50330005300 2005
50330005400 2006
50330005500 2007
50330038600 2007
50330005544 2008
50330038600 2008
50330005544 2009
50330038600 2009

Clearly there was upgrades to the cylinder through the years. But the basic 503 cylinder design was kept until 2015. From 2016 the power valve setup changed and the cylinder got the 504xxxxxxxx number matching the new motor design number of 504xxx...

When you compare the cylinder number (three first numbers only) to the engine case numbers you see that the cylinder upgrades did not adopt the new three numbers from the upgraded engines (512, 515, 523 etc.). This would indicate that the motor and cases were upgraded to fit new/modified parts, but the basic 503 cylinder design was kept. I do not have any deeper understanding of the KTM parts number logic (and at times they do not make sense if/when you try to figure out what motors they belong to), but I have noticed that when there is a major upgrade to the part the three first numbers also change. "Minor" upgrades to the part is reflected in the rest of the numbers. This was my logic when suggesting that any 503xx... barrel would fit your engine. If you go for a later model 503 cylinder you might find that as result of "minor" upgrades you also need to fit other later parts.
 
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