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Old 07-26-2012, 10:55 PM
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Default 1998 YZ250 cylinder on a 1990 crankcase????

     

Hi All,

I am looking for anyone that would have either first hand experience or
knowledge of the exact differences between the 1990 and the 1998 top end.

I have looked around a fair bit but I'm at a loss really short of just trying it.

I would like a nickel cylinder somehow and thought if the years match then
that would save throwing away all the good gear that I have put on this engine.

the part number for the 1990 cylinder is 3SP-11311-00-00
the part number for the 1998 cylinder is 4XL-11311-20-00
that replaced 4XL-11311-10-00

And it seems to be the answer for a lot of the parts, the first 5 digits are the same but a difference in the next two numbers, what do those 2 numbers mean?

all the powervalve appears to be the same design but part numbers are somewhat different.

I also can't find anywhere about the port timing differences
(or measurements)

If it just can't be done with a 98 then maybe another year???

Any help or ideas would be greately apprieciated!
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Old 07-27-2012, 09:17 AM
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I wouldnt base where you can or cant on part numbers. compare base gaskets first. the connection rods are different lengths. i want to say that the one on yours is the longer of the two, so you would need to make a spacer to go under the cylinder. i have no idea on the powervalve linkage but that should be pretty easy. back to the rod length: it seems like using the old rod was how they were building long rod 94-98 machines a few years ago. wiseco's site used to show lengths for their rods so you should be able to see for sure. the bore and stroke is the same on both engines.
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Old 07-27-2012, 02:50 PM
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Thanks for your info,
Yeah I have a long rod cylinder hidden away in a box somewhere, actually a 1988 model I think.

Base gasket looks the same but the part number is not, water jacket is on the same side and all the obvious things look the same.

I think I saw cylinder spacers for for the long rod kit for sale still somewhere to, I better have another look at that.
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