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don5154

Modify yz 400 to 426

8 posts in this topic

Hi All

Just pulled my beloved yz400 down and would like to convert it to 426cc. I know from scearching the posts that a 426 cylinder, piston, rod and crank pin will interchange.

Does anyone if I can use a 426 crank instead of rebuilding the 400 crank?

Thanks for reading this.

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Wow 440 cc's. Now if the bike were lighter and didn't have the manual decompression it'd still be competitive. For $550 that's probobly not a bad choice. I remember there was a 420 kit a while back.

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Yes there was a 420 or lets say 417,Some piston maf mite sill have some a round but ,why the 426 rod ,is because the 400 pin size was to small and would break.I had one of the first 450 kits in 98.

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Thanks Guys

The stock cylinder has a score mark. The shop manual recommends replacing it and the piston. I might as well go with the 426 mod for the stronger rist pin. The cost is about the same for a 426 rod, bearing, pin and labor as the new 426 crank assembly IF it it will fit. The right side of the 426 crank has a different part number.

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I think if you check you will find the 450 and the 400 use the same size piston pin.

I haven't started the motor yet but I have assembled a 400 with a 450 crank and a 426 cylinder and a 450 piston. Every thing turns over but I need to clearence everything and reclean the parts before I start it. And it has a 450 trans in it also. ?started? is that proper english? The 6mm bolt on the camchain side if the cylinder does not match the case. I will have to weld something here!

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Call powroll they can answer all your ? One thing you will find is the cam chain sprocket on the crank is wore out.

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Keep us informed how the 400 to 450 mod goes. You are very brave!!

Just learned that 426 crank will not fit 400 right side case.

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