2002 426f engine rebuild?


14 replies to this topic
  • marcmo0

Posted February 06, 2007 - 08:12 PM

#1

I have been reading through the posts and wondering about when it's time to rebuild the motor. I see a lot of folks have rebuilt the motor on their older YZF's and was wondering if it was due to lack of performance, starting issues, or is it preventative medicine. I have a 2002 426, and I ride a fair amount mostly trails and desert, with the occasional trip to the track. I take good care of it with regular oil and filter changes and valve clearance checks. It is super reliable and starts up first or second kick, valves are in spec, runs strong, etc. Should I be considering a rebuild anyway just due to the age of the parts? I was just wondering if the motors need a rebuild after X hours, or what the deal is? Thanks!

  • ISBB

Posted February 06, 2007 - 08:44 PM

#2

leak down test and compression check will tell you alot.. :censored: I would recommend doing those 2 to see if you really need to go past the valve cover as far as maintenance. :ride:

  • Goosedog

Posted February 07, 2007 - 04:55 AM

#3

I just rebuilt the top-end on my '02 last fall even though the bike was running fine. I estimated there were 300+hrs on the original piston and valves and did it primarily for maintenence reasons.

The book calls for a fresh piston every 50hrs if you race and every 150hrs if you just ride. Well at twice those hrs I thought it would be smart to go ahead with the rebuild.

After breaking it down I was amazed at how clean the internals were. The piston was only .003 out of spec and the valves about .004, timing chain even looked new. I probably could have gone another 200hrs with no problem.

Still glad I did it for the peace of mind factor and I did notice the bottom end got snappier again.

Moral of the story.....change your oil frequently and these bikes are bomb-proof.

  • Florida_426

Posted February 07, 2007 - 07:50 AM

#4

I'd keep an eye on the valve lash as you have been doing and check ring end gap to see if rings are needed. The only thing I can think of is the cam timing chain replacement. I have an 02 and I am going to do this to my scoot. Get GrayRacer's guide from here and it will be easy.

Bill

  • 642MX

Posted February 07, 2007 - 07:59 AM

#5

I have been reading through the posts and wondering about when it's time to rebuild the motor. I see a lot of folks have rebuilt the motor on their older YZF's and was wondering if it was due to lack of performance, starting issues, or is it preventative medicine. I have a 2002 426, and I ride a fair amount mostly trails and desert, with the occasional trip to the track. I take good care of it with regular oil and filter changes and valve clearance checks. It is super reliable and starts up first or second kick, valves are in spec, runs strong, etc. Should I be considering a rebuild anyway just due to the age of the parts? I was just wondering if the motors need a rebuild after X hours, or what the deal is? Thanks!




IMO they need valve springs, cam chain, and rings every year for an aggressive rider. You can tell a difference in a fresh motor. :censored:

  • Kyle Prior

Posted February 07, 2007 - 07:30 PM

#6

I was forced to rebuild mine... The bottom end siezed up.

  • MBrider426

Posted February 08, 2007 - 06:14 PM

#7

Ya I have an 02 YZ426 also and have never rebuilt it its seems to run great and start easy but i am begining to loose my peace of mind about how much longer it can hold out. I plan to rebuild it soon and wondered if anyone has looked into or done a high compression piston. Whats the word about this mod?

Visit the ThumperTalk Store for the lowest prices on motorcycle / ATV parts and accessories - Guaranteed
  • flintlock28

Posted February 08, 2007 - 06:18 PM

#8

Remember you'll need to run 100 octane fuel, if you go with a 13.5:1 piston.

  • gildnernorth101

Posted February 08, 2007 - 06:59 PM

#9

If Its Not Broke Why Fix It

  • 642MX

Posted February 08, 2007 - 07:26 PM

#10

If Its Not Broke Why Fix It



2 words: Preventative Maintenance.

You change your tires before they wear down to nothing, pop the tube and damage your rims.... Right?

Why not install new rings before the piston damages the cylinder and then seizes to it?

  • 642MX

Posted February 08, 2007 - 07:28 PM

#11

Ya I have an 02 YZ426 also and have never rebuilt it its seems to run great and start easy but i am begining to loose my peace of mind about how much longer it can hold out. I plan to rebuild it soon and wondered if anyone has looked into or done a high compression piston. Whats the word about this mod?


I'll never rebuild my 4 stroke without a high compression piston. They are noisey (bit of piston slap), but they really bring the bottom end and mid range to life. I use a Wiseco 13.5:1 piston. :censored:

  • 642MX

Posted February 08, 2007 - 07:33 PM

#12

Remember you'll need to run 100 octane fuel, if you go with a 13.5:1 piston.


Well, thats not exactly true. KX250F's come from the factory with a 13.5:1 compression ratio and Kawasaki recommends pump fuel for them.

I personally use race fuel for my YZF, my bike will ping when its hot and being lugged hard. I use race fuel for its purity, lead content, and its octane rating. :censored:

  • Kyle Prior

Posted February 08, 2007 - 08:25 PM

#13

Well, thats not exactly true. KX250F's come from the factory with a 13.5:1 compression ratio and Kawasaki recommends pump fuel for them.

I personally use race fuel for my YZF, my bike will ping when its hot and being lugged hard. I use race fuel for its purity, lead content, and its octane rating. :censored:


They probably have a bigger combustion chamber though...

  • grayracer513

Posted February 09, 2007 - 08:34 AM

#14

They probably have a bigger combustion chamber though...

Bigger than a 426??

Sorry, dude, 13:1 is 13:1, regardless of bore size or combustion chamber shape.

  • YZF MAD

Posted May 18, 2007 - 11:26 AM

#15

i have had to rebuild my moter on my 02 426:foul: as the bottem camchain spocket flew to bits:confused: so it is in the shop getting a new crank bearings conrod timeingchain piston@rings:eek: have had to do some sweet talkin to the misses:worthy: ]





Related Content

Forums
Photo

Michigan Motocross Tires by 288yz450


Dirt Bike   Dirt Bike Regional Discussion   North
  • 1 reply
Forums
Photo

Megabomb Fitment by 288yz450


Dirt Bike   Make / Model Specific   Yamaha   YZ 400/426/450
  • 1 reply
Reviews

Yamaha YZ450F 2017 by Chris.GVS


Yamaha YZ450F 2017
  • - - - - -
  • 0 reviews
Forums
Photo

Snake pit oct 30th by The Anvil


Dirt Bike   Dirt Bike Regional Discussion   California
  • Hot  293 replies
Forums
Photo

yz250x vs 450 4t comparisons (preferably desert riding) needed by JakeNorthrupYZ450F


Dirt Bike   Make / Model Specific   Yamaha   Yamaha 2-Stroke
  • 9 replies
 
x

Join Our Community!

Even if you don't want to post, registered members get access to tools that make finding & following the good stuff easier.

If you enjoyed reading about "" here in the ThumperTalk archive, you'll LOVE our community. Come join ThumperTalk today!

The views and opinions expressed on this page are strictly those of the author, and have not been reviewed or approved by ThumperTalk.