parts compatibility? KTM 250 vs 300??

[KTM Mike]

The other night while changing my oil on my 97 KTM 300EXC i had the misfortune of a surprise coming out along with the oil - several needle bearing rollers, not the cages just the roller so far (some of the shorter ones about 3/16" long and basically intact)! At this point i have no clue what specifically has happened - the bike had shown no signs of this at last ride, and I have not tore it down yet.

Coincidently - just today I came across the chance to purchase what might be a great parts bike for me - a 1997 KTM 250 MXC at what I hope to negotiate down to a great price. It needs a top end - supposedly the bore is good (was resleeved) so only needs piston and rings etc.

My understanding is that the 250 vs 300 really differ only in the bore - all the bottom end is identical. Is this true?

If so - could I simply put my top end on this 250? Would the exhaust valve linkages hook up? I could then temorarily and quickly swap that engine into my 300's frame etc and use it for the rest of the season. Or for that matter leave engine in the MXC's frame if all looks ok on it, stick my headlight, taillight and plates on it and be ready to roll.

I realize the MXC and EXC have different gear ratios - but shouldn't I be able to swap these as needed?

What about other parts - such as suspension (perhaps different valving with MXC?) and other chassis parts?

Any advice appreciated! I want to get my bike running quick so I can still do my last two races or so of the year. I can then tear into my 300 over the winter and fix it up right. What crappy timing! I have a race I planned on just 3 days away and another one week after that.

 

[KTM Mike]

man...somebody's gotta know if the 250 would be compatible with the 300... my shot at buying the 250 wont last to long... anyone out there?????

I notice in the Chapparal and Dennis Kirk catalogs they list replacement rods for the 250 and 300s with same part #s - but I dug through my service manual (I have a 96 manual for my 97 so may not be absolutely correct!) and found they show the stroke of the 250 different than the 300 - am I reading this correct? If so - could i simply plop my 300s crank assembly in the 250s cases?

anyone????!!!!!

 

[P_Taylor]

I think the stroke is also different on the 250 and 300 by a few milimeters.

I may remember wrong but I didn`t think KTM made a 250MXC until `98. Could it be a SX or an EXC someone has pulled the lights off of.

 

[ryno_co]

Mike

I checked my spare parts manual for the 97 250/300/360 and found the following differences:

1.Crankshaft
2. right and left side brackets, r and l control shafts, r and l gear segments and the control flap. these are all part of the pwr valve assembly


The tranny appears to be the same for all exc models and I find no mention of a 250 mxc, only the exc and the sx. Hope this helps somewhat. I have no experience swapping parts between the 250 and 300 I'm only quoting the manual. Good luck.

 

[KTM Mike]

thanks guys... gives me what i need and confirms what i since guessed. I still may buy the 250 for beater bike to play around on then sell it.

now here is the next puzzle - I torn down the 300 today... split the cases looking for the source of those rollers - and try as i might i absolutely can not find a messed up bearing anywhere!!! I have looked over and over again, picked through the repair manual - no luck - everything seems perfect! I dont get it - they came from somewhere... but where? I finally decided to sleep on it and look again in the morning - maybe i will find it then or am i just going nuts? how could this be?:(