2002yzf426-engine rebuild?


13 replies to this topic
  • doucesics

Posted March 09, 2008 - 10:31 PM

#1

hello tt! i am new to this forum , and had a question for any yzf 426 experts? i recently pulled the head off to adjust the valves but the head was beat up a little(not cracked) i have owned this bike for 4 years and have had 2 of them(great bikes) anyway the cam followers are warn also? so is it time to do a complete or has anyone had luck doing just the top end? rings ect,new head,cams ect or should the whole thing be done or how can i check the bottom end play! mind you this bike feels good but i definetly have put the miles on it! consructive feedback appreciated cheers....whats others expierience with these?:thumbsup:

  • grayracer513

Posted March 10, 2008 - 06:38 AM

#2

It's probably a good idea to replace the rings, at least, and a piston for good measure. Check the condition of the cylinder. Check the crank per the manual.

If you need a manual, download one:

http://www.yamaha-mo...ice/manuals.jsp

I'm puzzled by your statement that you pulled the head to adjust the valves. You can't adjust the valves with the head apart (although you can do it on the bench if you assemble it), and if you mean you pulled the cam cover, I don't know what you saw that was "beat up".

  • doucesics

Posted March 11, 2008 - 05:27 PM

#3

hey thanks for your reply ! yes i ment the inside of the cam cover is beat up! but you probably knew that ! what is the best way to check for bottom end play!

  • klxnewguy

Posted March 11, 2008 - 07:18 PM

#4

Wow, I was just going to ask this question as well. I have an 01 426, starts up fine but the valves have NEVER been checked. I'm thinking about stipping the whole thing down and painting the frame up etc.. so I was thinking about maybe changing out the cam to the 03 but what else should I do?? On one hand I'm thinking if it's not broken don't fix it but on the other hand I don't want to wait until it's too late. What do you think and what would you do??:thumbsup:

  • doucesics

Posted March 11, 2008 - 10:19 PM

#5

yeah a friend of mine i ride with(frenchy) says that a bottom end is usally good for four years, but another mechanic friend says to do a rebuild top end and just check bottom end play! i mean u know what they say about opinions! but yeah don't want to see it granade! but there is no signs? maybe i am being over cautious? to me it is a bike worthy of rebuilding I have done a few mods and like the way it is pullin!!but if she is coming apart the frame is gettin powder coated black ! to match the black plastic seat and bars and maybe swing arm! what are tell tale signs on these engines there could be problems ahead?:thumbsup:

  • klxnewguy

Posted March 12, 2008 - 08:30 AM

#6

Is the best way to go to maybe have them do a top end and then while it's open check for play on the bottom end or what? Do they have to split the cases etc.. to do the bottom end? I like the powder coat idea, I'm thinking the same thing.

  • grayracer513

Posted March 12, 2008 - 09:42 AM

#7

Recommendations for rebuilds based on age or time on the engine are guidelines only. The only outward symptoms would be a very gradual loss of performance, increase in oil consumption, or in some particular engine noise.

Beyond that, only disassembly and inspection can accurately determine what needs to be done, and even then it can be difficult to tell. In the past, parts such as the cylinder and valves could be measured for wear, and the wear that was found compared with guidelines for how much was tolerable without some correction. Now, however, with the use of very thin hard coatings on cylinders and valves, any wear you find on those parts is generally an indication that they need replacement, as once the coating has worn through, the parts will not last.

Rolling element bearings are much the same. It is basically impossible to tell by looking at one how much longer the bearing will go without suffering a spalling failure (the flaking off of the hard surface of the balls or races), even if it shows no wear.

If the engine is apart, you can check to see what the rod clearance is by the methods shown in the manual while the crank is still in the engine. You can measure the ring gap to gauge their condition, and you can measure the piston, check the valves, camshafts, etc. Beyond that, it's a your-guess-is-as-good-as-mine judgment call.

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  • klxnewguy

Posted March 12, 2008 - 01:51 PM

#8

Gray - what would you do?

  • grayracer513

Posted March 12, 2008 - 04:08 PM

#9

Me? Sell it and buy a newer one. :thumbsup:

  • 642MX

Posted March 12, 2008 - 05:50 PM

#10

Me? Sell it and buy a newer one. :thumbsup:


:eek: :D :ride:

  • grayracer513

Posted March 12, 2008 - 06:31 PM

#11

:thumbsup: :eek: :D

I wasn't kidding. That's the approach I took to my '03 when it got long in the tooth. Of course, there were other things, like the fact that it was never going to handle like an '06, too, but that is what I would do and have done, usually.

  • 642MX

Posted March 12, 2008 - 06:46 PM

#12

I wasn't kidding. That's the approach I took to my '03 when it got long in the tooth. Of course, there were other things, like the fact that it was never going to handle like an '06, too, but that is what I would do and have done, usually.


I know, but it was still funny. :thumbsup:

I figured that the 5 speed would be more of an advantage in the desert, rather than the difference in handling. :eek:

  • klxnewguy

Posted March 12, 2008 - 07:29 PM

#13

Gray, I have that thought going through my head but I don't know what to get. I put a flywheel weight on my bike as I ride about 60% trails. Also, I like the green sticker as I live in CA but I just found out that the places I ride in Nor Cal don't even limit the red sticker times of the year. So, with that said what bike would you recomend I move up to? Maybe on 06 YZ 450 F? What do you think I would gain?:thumbsup:

  • grayracer513

Posted March 12, 2008 - 08:25 PM

#14

...An 06 YZ 450 F? What do you think I would gain?:D

Power, handling, suspension, lower weight, a bike that you can ride longer without getting tired. Otherwise, not much. :ride:

The Green Sticker issue is real in parts of CA, and how important it is depends on where you ride. Likewise, a 426 is a great motorcycle, every bit as good as it was in the first place, and if you choose to put the money into that, it's a defensible choice.


I figured that the 5 speed would be more of an advantage in the desert, rather than the difference in handling. :eek:

The 5 speed definitely helps, but handling is more than cornering (and there really are corners in the desert, sometimes big, fast corners). The suspension is so far ahead of anything that I've ever even seen done with the old stuff, and the bike behaves so well at speed in the rough that I just don't get as hammered as I used to. That's an advantage. :thumbsup:





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