94-99 CR250 Engine Question

wacker
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wacker
I figured more people viewing this category would actually know than in the Tech Help section.

So, I have a running 94 but the top end is on its last leg and is sleeved already. I also have a 99 donor motor completely pulled apart. I know the newer head is different but the 99 has a flat top piston compared to the domed one my 94 has.

The 94 needs a new top end and I have a 99 cylinder, brand new flat top piston and gasket kit sitting here. Anyone have any opinions in what direction to go with this? Ultimately I am pulling the 94 apart also and building one motor out of the two but I really want to race it next weekend at Day in the Dirt and would rather it be fresh.

Thanks!
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scooter5002
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scooter5002 11/19/2017 4:48pm
11/19/2017 4:48pm
Given that they are basically the same motor, could you not put the new piston, cylinder, and head on the 94? Same rod, same stroke. For one day, that's what I'd do.
wacker
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wacker 11/20/2017 10:04am
11/20/2017 10:04am
scooter5002 wrote:
Given that they are basically the same motor, could you not put the new piston, cylinder, and head on the 94? Same rod, same stroke. For...
Given that they are basically the same motor, could you not put the new piston, cylinder, and head on the 94? Same rod, same stroke. For one day, that's what I'd do.
The 99 head is taller and has a different head stay mount. Not sure how much difference the head is cut for the different piston, but I believe the difference in height is mainly because the water jacket is larger. Basically just need to see if anyone knows how different the head is cut and what issues could arise from the 99 piston, 94 head, if any. Just asking because I figured someone here probably knows and I don't have time at the moment to figure it all out.
scooter5002
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scooter5002 11/20/2017 1:13pm
11/20/2017 1:13pm
That kinda sucks. I'm not sure mixing heads and pistons is a good idea, because squish and compression will change, I'm guessing.
TTperra
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TTperra 11/20/2017 3:43pm
11/20/2017 3:43pm
Make a headstay?
Dont have to be pretty, just work..
Measure squish when you assemble, so you dont get a suprise.

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tuggy450
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tuggy450 11/20/2017 7:15pm
11/20/2017 7:15pm
pretty much sums it up you can use the 99 cylinder with the 94 head and piston, the head studs are alittle longer might need washers everything will bolt up fine. otherwise you modify the head stays, stay with all 99 stuff.

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