KX 250 Mismatched Crankcases

[Kawafornication]

Has anybody ever made two different year crankcases match up with a helping hand from a Dremel? I have a KX 250 1991 right side and 1990 left side and am thinking to cut out the bit that does not match up??  

[sandblaster]

I believe the older cylinder does not use floor ports.
If you are using the older cylinder you shouldn't have to worry about it.
If you are using the newer cylinder you should make the cases match as long as there is plenty of material.
It looks like there is.

[Kawafornication]

Great I will take some pictures when I get the engine taken to bits, these cases are meant to be going on the donor bike for resale, not sure which cylinder is going on them yet unless I am better off leaving the 90 cylinder with the 90 crankcases due to floor ports (what ever they are) I thought that the case with more metal was the 91 side?

PS, it says

"An Error Has Occurred!
The upload folder is full. Please try a smaller file and/or contact an administrator."

so cant add a picture

[sandblaster]

Floor port?
Take a look here

http://www.oem-cycle.com/forum/viewtopic.php?f=110&t=1480&p=7789#p7789

[Kawafornication]

Thanks for taking the time to do that, does that mean you can use the 1991 cylinder on the mismatched 90/91 cases (not going to lose performance as never had extra floor ports) if so with or without the metal from the 91 case ground away? or better to remove the extra metal for flow reasons

Knowledge is power, i'm still learning 

PS, I assume that also means if you used a 1991 cylinder on 1990 crankcases you would be losing performance as originally meant to have the extra floor ports??

[sandblaster]

If your cylinder has floor ports, you will need to grind the cases out to match, or you will loose some power.
If your cylinder does not have them then there is no reason to worry about the cases.

[motorsickleman]

put all your case bolts in to make sure they all line up.  i literally just ended up with mismatched cases at work and i thought all i had to do was the porting.  i have an 89 left case and what was supposed to be an 88 right case but looking thru ebay and also your pics here it seems i have a 91 right case.  i started porting the case to match and had an idea that i should check the case bolts, three of them do not line up.  i drilled them off center with a 1/4" bit and used a helicoil kit to insert steel inserts in the larger holes.  if yours is the same scenario you'll see what i am speaking of. 

[motorsickleman]

btw the older cylinder has floor ports.  looks like 91-96 did not have floor ports.  my 89 case looks like your 90 case with the port cut out, my other case half has the extra material, flipping thru ebay listings confirms for me that 91-96 did not have the floor ports.  hope this helps, i am halfway thru porting mine so i'll try to post some pics when done.

[Kawafornication]

Thanks seems to be a common thing, when I took the cylinder off yesterday I found that it already had mismatched cases but the other way around, I already knew that the 90 and 91 halves would work together as seen it on another forum!

I am guessing it is not worth repairing the sump plug to match up the two 1990 halves as there is so much side play (must be 2mm or so) on the crank on the built engine I would am thinking it shows signs of knackered cases, the 1991 half is definitely junk!


The cylinder was a 1991 with no floor ports, shame as been in the hands of an old school tuner from the UK called Stan Stephens, I really wanted to keep that one for my 1990 bottom end!

[motorsickleman]

ok, got side tracked for a bit, just finished assembling the bottom end of this 89 kx250 engine.  to review, this engine had a blown out case under the crankshaft, when brought to me it had already been welded but i didnt feel it was a clean enough job to reuse it.  i sourced a case half from ebay, supposed to be an 88' case half, turns out its a 91' which did not have floor ports like the prior engines.  3 things need to be done to make this work.  1.  port the case to match the original design.  2.  3 of the case bolts dont quite line up when using the new vs old cases together, if using both newer cases then this isnt a problem.  drill the holes off center 1/4" bit, helicoil the new larger holes to take them back down to threaded 6mm.  3.  newer engines use alignment dowels under the cylinder whereas the older floor port style cases dont have this.  difference is, if you are replacing studs you must use longer studs.  the holes made for the dowels cause the threaded portion to sit lower for the newer cases, i put the new 89' studs in and they wouldnt reach far enough past the cylinder surface to provide a proper connection.  i ended up using the longer of the two 89' studs and placed it in what would be the shorter studs position (original 91' stud is not available  )  i have on order now the longer of the two studs from 91'.  i have not completed this engine but the bottom end is complete now, crank rotate freely, trans shifts thru all the gears as it should no other alignment issues.  reason for all this work is that i could not acquire the original case, i believe 88' 89' 90' are the same but seem to be very scarce, very often, i run across 91+ cases so this is a possibility for those in need of cases.