2001 YZ426F Frankenstein Engine Rebuild


5 replies to this topic
  • 575

Posted August 31, 2009 - 10:20 AM

#1

2001 YZ426F - timing chain tensioner broke (we think) and piston, head/valves, cams, cylinder were all destroyed. We got a used engine off of ebay that has a bad 2nd gear. We're putting the good top end on the bottom end of the engine that was destroyed. We're planning on splitting the case of the engine that has the good bottom end to make sure no chunks of metal are floating around down there. Basically, it's a complete tear down and rebuild and frankensteining one engine with the other. What parts should definitely be replaced while we've got the engine completely apart (top end and bottem end)?

  • grayracer513

Posted August 31, 2009 - 11:10 AM

#2

I would start with the assumption that the crank on the engine that dropped the valve was damaged, and basically alter my strategy to one of putting the good transmission in the one that lost 2nd gear.

  • mxmaddman

Posted August 31, 2009 - 01:23 PM

#3

Well... once you have the good bottom end assembled assuming everything clutch and all is within Yamaha specs you will need a top end kit, timing chain and check your valve clearances, maybe some seals.... don't over torque the cam caps, check or replace the tension-er and guides and you should be ok.

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  • 575

Posted August 31, 2009 - 04:19 PM

#4

Can I use the timing chain, tensioner, and guides from the engine with the good top end or should I replace them as a precaution? They all seem to be in reasonably good shape.

  • grayracer513

Posted August 31, 2009 - 07:36 PM

#5

Replace the chain regardless.

  • mxmaddman

Posted September 01, 2009 - 05:05 AM

#6

Can I use the timing chain, tensioner, and guides from the engine with the good top end or should I replace them as a precaution? They all seem to be in reasonably good shape.


you want to replace that chain every 40 hours man..never reuse a chain. Thats most likely what caused your other engine failure. Inspect the lower crank sprocket on good motor and make sure its not worn out. By worn out I mean starting to "sharpen" the teeth will look like they are pointy. I have seen some so bad that they had trouble fitting through the hole in the case when i took them out. your sprocket teeth shouldn't give you trouble clearing the case when you remove the crank unless they are worn.





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