99 yz 400f top end rebuild


7 replies to this topic
  • boricua1

Posted January 01, 2012 - 10:50 PM

#1

I have a 99 yz 400f took the top end off due to a base gasket leak come to find out that wasnt the only thing wrong i a broken piston ring and piston slap and a damaged head from the piston slap and excessive wear were the cams sit. NOW MY QUESTION IS would i be able to stock bore 426 cylinder and piston with stock 400 crank and heads or would i have to chenge all that???:bonk: anything helps. Thanks.

  • aclown

Posted January 02, 2012 - 12:01 AM

#2

From my understanding the cylinder will bolt right on. But you can not use the 426 piston with the 400 connecting rod due to the different piston pin diameter.

  • grayracer513

Posted January 02, 2012 - 08:19 AM

#3

From my understanding the cylinder will bolt right on. But you can not use the 426 piston with the 400 connecting rod due to the different piston pin diameter.

That part is true, but you can have the crank rebuilt with the 426 rod to get around it.

  • bonehead7101

Posted January 02, 2012 - 09:12 AM

#4

Sounds like too much work .... imp keep it stock. It will probably run longer.

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  • boricua1

Posted January 02, 2012 - 04:07 PM

#5

What about the head would i have to change anything up there as in valves or cams or anything else? or would i have to buy a 426 head also

  • 2grimjim

Posted January 02, 2012 - 04:18 PM

#6

I believe the 400 and 426 heads will interchange.

  • SWIGIN

Posted January 02, 2012 - 04:36 PM

#7

What about the head would i have to change anything up there as in valves or cams or anything else? or would i have to buy a 426 head also


I have 3 buddys who all converted yz400 motors into 426cc and they say all you need is a 426 cylinder, piston and rod.

  • boricua1

Posted January 02, 2012 - 09:25 PM

#8

As for timing chains Wat would u say is the best?





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