Maintenance & Technical > KX250 / KX125

92 cylinder question

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Redrodent:
I have a 91 kx250. The 92 engine is externally the same, it didn't change until 93 but ...

 The 92 has a 2mm longer stroke crank and is available (92-01)   so....

I'm assuming the 92 cylinder is a one year part, 2mm taller with completely different porting?

With the cylinder being the only rare item, would this be an option come rebuild time? 92 cylinder and crank with my 91 cases

CR480R:
I would consider it an option.. I was going to go that route with my engine, but it was too expensive to track down all the needed parts... I wanted to get a late 90's top-end, but most of the ebay sellers tend to sell the head, powervalves,water elbows, and covers all separately... My main attraction to the swap was that the '92-05 cranks are very plentiful... I have checked and there is plenty of room in the '91 cases for the bigger stroke... I had even considered using the '88-91 cylinder with the 72mm crank and having the porting corrected for the stroke...

Redrodent:
Thanks, yes the crank is the attraction. Can you confirm that the 92 cylinder is taller, (correction, it would only need to be 1mm taller) or did Kawasaki just jack up the head/base gaskets? Early bore and late crank = 265cc. Could be fairly cost effective if rebuilding anyway. Finding someone who understands how to port it would be the hard part.

edit: ran the part #s through Kawasaki. 91/92 head and base gaskets are the same.

Redrodent:
For any 89-91 riders, here's what I've found so far. Some one gave me the 91 and 92 piston heights. They're the same. I got my hand on a extra 91 cylinder and measured the ports.

Based on a 72mm stroke you could raise the cylinder 1mm and the port timing would be a non issue. You might lower the main exhaust port 1mm but wouldn't have to. And the transfers are already 3mm below the piston at BDC, so stroking and raising the cylinder should improve their flow. The only issue would be increased compression, guessing 5- 10%.

 I now believe for 92, Kawasaki just cut the bottom of the jug 1mm less (also 1mm smaller bore) and left it at that.
 At this point in my research, using the newer 72mm crank in my 91 should be a fairly bolt together affair.

CR480R:
So an extra thick base gasket should be all you need???

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