Engine rebuild question


8 replies to this topic
  • upthemaiden

Posted December 23, 2011 - 06:20 AM

#1

I'm rebuilding a 2001 yz426 motor that needed a new crankshaft. I got it apart, split the crankcase and swapped the crankshaft no problem. Bolted it together, bolted in the shift segment and shift guide, then slide in the shift rod. Just to test it out I tried putting the shift lever on the left side but I can't get it to shift through the gears.

My question, is at this point, should I be able to shift the motor through all the gears, or does it stay locked into neutral for some random reason until I get something else on there??

  • upthemaiden

Posted December 23, 2011 - 06:24 AM

#2

I assume I need to split the cases again and reset something. Before I pulled it apart the first time it was in neutral, and then as I tried to remove the bolt for the segment it rotated it all the way counter clockwise until it stopped spinning, so the bolt would have something to untwist against. I assumed as I tried to tighten it, it would rotate all the way clockwise before it tightened, but it didn't. When I pulled the cases apart some of the transmission lifed up a few mm or more as it tried to stay in the right side case. I assumed it was still in place because it would spin freely, but I know there's a chance something moved and needs reset. I was hoping to not touch the transmission at all, just leave it in place but want to make sure it's working right before I put everything else back together.

  • 2grimjim

Posted December 23, 2011 - 09:01 AM

#3

When the engine is re-assembled and dry, the tranny may not function very well. You will have to turn the transmission shafts while pushing the shift lever the get it to change gears. It migh seem that it's not shifting well, but if you can get it through all 5 gears and back to neutral, you should probably be ok.

  • upthemaiden

Posted December 23, 2011 - 02:44 PM

#4

Thanks! I'll give that a try

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  • grayracer513

Posted December 23, 2011 - 08:58 PM

#5

Notice that the shift segment is indexed to the shift cam by a small pin, so that the various positions on the two parts are correctly oriented. Be sure you haven't misaligned this and damaged the pin.

  • 2grimjim

Posted December 23, 2011 - 09:07 PM

#6

Notice that the shift segment is indexed to the shift cam by a small pin, so that the various positions on the two parts are correctly oriented. Be sure you haven't misaligned this and damaged the pin.


Yes! Very important! I made the mistake of tightening the sector bolt when it wasn't aligned with the pin and had to split the cases (again) to fix it. If the pin get pushed into the shift drum it's a huge pain in the butt to fix.

  • upthemaiden

Posted December 24, 2011 - 05:55 AM

#7

I made sure to get that pin lined up so I should be ok there. I tried to spin the transmission by hand as I shifted but it still didn't want to go into any other gears. I might have to split the cases again and make sure the transmission is set right. I guess it won't hurt to see exactly how the transmission is configured in there. That way when I find a good deal on a wr426 transmission I won't be hesitant to pull the motors apart and swap them.

  • BBrown626

Posted December 25, 2011 - 11:54 AM

#8

I made sure to get that pin lined up so I should be ok there. I tried to spin the transmission by hand as I shifted but it still didn't want to go into any other gears. I might have to split the cases again and make sure the transmission is set right. I guess it won't hurt to see exactly how the transmission is configured in there. That way when I find a good deal on a wr426 transmission I won't be hesitant to pull the motors apart and swap them.


Don't go any further with assembly if you can't get it to shift through all the gears. Unless of course you want more practice! Been there done that with my son's 85.

Like another post said, turn the countershaft in the proper direction while shifting and you should be able to go through all the gears. It may be a little rough, but if you can't do it, you have something together wrong.

Good luck. Once you do it a time or two, engine rebuilds are fairly simple.

  • upthemaiden

Posted December 26, 2011 - 03:56 PM

#9

Good luck. Once you do it a time or two, engine rebuilds are fairly simple.


I'm pretty surprised how few parts there are inside this motor. I assumed it would be way more involved.

When I bolt the crankcase up it'll run through all the gears easy as can be if I spin the gear indicator on the left side of the motor. Once I bolt the segment onto the right side it seems like there's a lot of resistance on the motor. Closer but I'll still have to figure out why it's not shifting smoothly once it's all back together.





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