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marcmo0

2002 426f engine rebuild?

15 posts in this topic

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!

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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:

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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.

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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

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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:

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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?

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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?

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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:

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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:

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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...

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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.

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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: ]

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