Putting new piston in my 2011 YZ450 today. Any tips and tricks?


13 replies to this topic
  • torkd14

Posted December 14, 2014 - 09:51 AM

#1

Never pulled the head off a 4t before. Anyone have any tips or tricks to make this as simple as possible? Thanks.

  • grayracer513

Posted December 14, 2014 - 10:16 AM

#2

Read the whole procedure in the manual first. Then read it again. Then do it.

The biggest challenge will be compressing the oil rings. Always stuff rags or something in the crankcase under the piston to avoid dropping a circlip into the sump.

  • torkd14

Posted December 14, 2014 - 05:08 PM

#3

So I got it apart, everything went smoother then I had anticipated. Here are some pics of my cylinder. Is the vertical line a bad thing? It says in the manual vertical scratches are bad and to replace cylinder but you can still see the cross hatching so the vertical parts almost look factory. Measurements are all in spec 97.00mm. Thanks Grey. ImageUploadedByThumper Talk1418609714.011164.jpg ImageUploadedByThumper Talk1418609727.385417.jpg ImageUploadedByThumper Talk1418609740.134053.jpg

  • SAthump

Posted December 14, 2014 - 06:13 PM

#4

Those aren't scratches, just aluminum from the piston.

Clean it and ride happy

  • grayracer513

Posted December 15, 2014 - 07:55 AM

#5

If you run a brush hone through it, it looks like it will clean up pretty well.  I circled the two areas that concern me the most.  If these two spots will disappear after less than 15 seconds total time with a silicon carbide hone (10 with aluminum oxide) you should be OK.

 

 

Attached Thumbnails

  • bore.png


  • torkd14

Posted December 15, 2014 - 09:07 AM

#6

If you run a brush hone through it, it looks like it will clean up pretty well. I circled the two areas that concern me the most. If these two spots will disappear after less than 15 seconds total time with a silicon carbide hone (10 with aluminum oxide) you should be OK.


Ok awesome, I did order a flex-hone with my parts luckily so I will do that for sure. Hopefully it cleans up. Thanks again, super handy being able to talk to someone with knowledge on this stuff.

  • grayracer513

Posted December 15, 2014 - 09:53 AM

#7

Review this post for details on honing:

 

http://www.thumperta...d/#entry3565759

 

Most important, after selecting the right grit and abrasive, are:

 

  • Low speed drill only
  • Move the tool up and down the bore as it turns to establish the cross hatching
  • Use the tool wet
  • 4-5 seconds max, then check


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  • mch

Posted December 15, 2014 - 10:46 AM

#8

I just did my WR and a friend recommended I insert the circlip on one side of the piston, then insert the piston w/rings into the cylinder while they are off the bike.  Then stick the cylinder / piston combo onto the connecting rod and insert wristpin / last circlip.

 

I did that method and it seemed to work pretty good.  Just make sure you stick a rag or paper towels into the case in the event you drop the circlip.



  • grayracer513

Posted December 15, 2014 - 10:56 AM

#9

That works OK, but the problem is that the wrist pin bore is so close to the oil ring groove that the oil ring has to be down out of the actual bore and into the chamfer at the bottom of the sleeve, anyway, so you don't get as much help from doing that as you might want. 

 

Putting a couple of thin pieces of wood (or a single piece with a slot in it for the connecting rod) under the piston to give it somewhere solid to sit on while you work the jug onto it is another good approach.

 

The thing you really have to watch for is snagging the ends of the oil ring and rolling the ring out of the groove.



  • rocker

Posted December 15, 2014 - 10:10 PM

#10

The cylinder looks like it should clean up very well.

I have access to a hone we can use tomorrow when you come to pick up the tank and exhaust for the snowbike.

See ya tomorrow bud!!

 

Craig



  • torkd14

Posted December 22, 2014 - 08:08 AM

#11

Got the bike back together and it runs great. The honing cleaned the cylinder right up. I broke it in for an hour on tires and then put the snow bike kit on. Put a good 4 or 5 hours on it yesterday and it didn't miss a beat. ImageUploadedByThumper Talk1419264514.586241.jpg

  • stevethe

Posted December 22, 2014 - 04:33 PM

#12

Got the bike back together and it runs great. The honing cleaned the cylinder right up. I broke it in for an hour on tires and then put the snow bike kit on. Put a good 4 or 5 hours on it yesterday and it didn't miss a beat. ImageUploadedByThumper Talk1419264514.586241.jpg


What's the name of that trail snowy. That's quite a bit of snow you got there.

  • torkd14

Posted December 22, 2014 - 04:43 PM

#13

What's the name of that trail snowy. That's quite a bit of snow you got there.


It was in a riding area in Fernie, British Columbia.

  • Falcon 1

Posted December 22, 2014 - 04:50 PM

#14

A good honing stone will make that cylinder look like new.







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