99 KX250, HELP identifying parts...

[wombat]

I'm fairly new here. But I have only heard good things about this site, so now I seek your assistance. I bought this bike, thought it was a 98. find out its a 99.. no big deal. But the motor came in boxes. 2 of them in fact. I found out one motor was the original, the other is a 90-91 model. I am trying to figure out witch is witch now, because I think my (according to the OP) good bottom end is put together with both engines.
I was told when I got it that it needed an inner clutch cover. so I bought one (yet to see if it fits). but I got to looking at my motors, and thats when I found one of the (the supposed good one) to be a 90-91 model. That got me in the mood to say the hell with it and do a 500 SFC. BUT while looking at it today, I realized that the engine cases don't really match up. It is possible to have the (91-90) H model case half bolted to the (99-02) L case half? and if so, what internal parts could be the same? if most of what I have good is 99 model stuff then I have no problem fixing the motor I have opposed to completely replacing it. I just got to find a sure fire way to tell the difference.
The other problem that I have is the cylinders. I don't know wich one is old and wich one is new. even though there is a distinct difference. Hopefully these photo's will help someone with more knowledge then I figure it out.
This is the side that I THINK might be the L model.


You can see here how they don't really line up good.


and here.


This is the proposed H side.


Notice the two clutch baskets. The bearings on the shaft in the middle of the pic on fit in one.

Not that one.
These are the bearings.


and here are the cylinders.

I think this is the H model cylinder.


and of course, cause I'm a pic whore. Heres the bike. only got 300 bones in it, so if I am way off and have to buy a motor, I'm not but hurt.

[wombat]

I was able to find out by OEM-cycle's ID page that the cylinder pictured is the correct one for a 99 model, so thats a good thing, cause the other one looks like it was taken off with a hammer...

[shookyd]

Don't think the cases will work if they are from models that far apart.  The shifter forks changed in '96 I think.  I bought stout of cases on eBay that are in great shape,both we're marked 1995 KX250 but one case has larger shifter forks than The other. So I am still looking for a right case half with the small shifter rods or a later model left case plus the bigger shifter rods.  Good news is I can have two good sts of cases and I got the insides for both.

[sandblaster]

97-04 USE A LARGER SHIFT FORK PIN & 1 LESS CASE BOLT
As a minimum you would have to either shim one side or turn the opposite ends and then you would have to worry about the shif fork alignments, ect.
Not saying it couldn't be done but is it worth it?

[motopunk]

the 90/91 engine-cases are in diference to the 92- 96 and 97-2004 cases like night and day . more similar to the 87-89 engines.

only some things like the transmission shaft and gears are interchangeable .also cranks are diferent with shorter stroke in the older models. and never break the marriage of an good working pair of engine-cases