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642MX

Yz444f

12 posts in this topic

Yes, I searched and didn't find much.

I ran across a cylinder and I'm thinking of making a YZ444. What can be expected of a YZ444? More bottom end? More mid range? Is this worth doing? or a waste of time? :excuseme:

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It's a 4.2% increase in displacement. Most of the increase will be in teh low and middle ranges, because at higher speeds, the limitation is more about the cams and head, and the ability to move air in and out, and not so much about the size of the engine.

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I suggest doing both the big bore and a set of cams at the same time.

I've already got the cams. But thanks for the suggestion. What do you think of the big bore kit?

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Lukes Racing is sending me his 440 kit now! It is the cylinder bored and new nikasil and a 97mm wiseco 12:5/1 piston 415.00 with gaskets. Oh and a Falicon welded balanced and polished crank with a 2001 right side (ditches the woodruff key) will be installed.

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I've got the 440 kit, its Ouwsome ! lots of low end and mid.

Good to hear that you like it.

I can't wait to send the cylinder off and get the 444 treatment. I was going to wait until winter, but maybe I'll do it sooner. :excuseme:

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I hear from everyone that this is the hot ticket for these bikes! When My motor goes i'll be doing this! Let us all know what you think...

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I, too have the Luke's kit with 13.5:1 compression....and Hot Cams. It's truely a grat combination. When I added the hot cams, the bike really woke up in the mid range and big end, without a loss in low end, and it revved to the limiter a whole lot quicker. With the big bore kit, it doesn't rev quite so quick. With stock gearing, first gear became almost useless, as the back tire would break loose under all conditions. I went up a tooth on the c'shaft sprocket and can still break the back end loose or hoist the front at any time in any gear!

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Sounds Awesome but how about reliablility>

How's the riding in Qatar? Been thru Doha once...and once was enough...

As far as reliability, I did mine maybe a year and a half ago and have somewhere between 1200-1300 miles of So Cal desert riding on it...fast trail riding (at least fast for a fat old man) and it's still rock solid. I ran a compression test right after break in, and ran another one not too long ago, and things have not changed one bit. It doesn't use any oil. No issues at all so far (knock on wood) other than it takes a bit more of a kick to light it off.

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