Ive just bought a yz400 with a 426 engine as a second bike to my wr450 and was wondering if the 400 head will fit onto the 426. i bought this bike as a project knowing the engine was blown up. i also got the original 400 engine with the bike. the 426 has droped a valve damaging the piston and head. so if possible i want to fit the 400 head onto the 426 with new piston and conrod and big end bearings.if this works i will end up with a cheap bike. considering i paid only 1000 dollars for the bike with 2 engines. if anyone could answer this question it would b greatly appreciated.:worthy:

what years are the engines? I checked the part #'s on a 99 and a 02 and they are differant

1999 5BE-11102-10-00

2002 5be-11102-50 or 5fg-11102-20

I think I would just take them both off and set them side by side to see what is differant . I think it's something to do with the decompression but I am not sure . I have heard of people useing parts from 426's on 400 and the other way too . I think it will work but something is differant.

the 400 is 98 and the 426 is an 02 model. they look the same and all. from wat i have gathered so far the only differences are the 400 has a little pipe coming out of the intake were the 426 doesnt, it must be for the carby and the 400 has stainless valves weras the 426 has titanium. i have also found that the difference in compression and sizes between the 400 426 and 450's are the 400 has a smaller bore and stroke with the same head as the 426 and 450 and the 426 has the same size piston as the 450 but has shorter stroke. i just wanted to make sure the haeds were the same before i go spendin the cash to fix up the engine then finding out the head doesnt fit. thanx for ur reply. i guess i should just go for it cause they do look the same.

I am 99% sure the old head will fit. Other than the valves they are the same.

Just make sure that the valves and seats are good before you put it on. Also make sure the cam journals are clean and don't swap the cam caps between heads.

Have fun

Got a 400 head on my 444...with the vacuumport plugged.

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