I think it's time to rebuild


9 replies to this topic
  • Arctic79

Posted April 05, 2007 - 03:57 PM

#1

Hey everyone, just wanted to say hello since this is my first post. I've been floating around for a while and reading this or that, so I figured I may as well join up.

Anyway I think I'm due for a rebuild on my '00 yz 426 since it probably has 150-200 hours on it. My question is how much am I probably going to have to throw in? I already plan on doing the valves, springs, piston & rings, but do I have to worry about the crank and rod as well (do these rods tend to stretch)? Also how are the Wiseco 13.5:1 pistons, are they worth it, or do they give much gains?

Any additional advice or recommendations would be appreciated as well

Thanks

  • CaptainKnobby

Posted April 05, 2007 - 04:18 PM

#2

Yep! you are probbally dou for a top end rebuild but as far as the bottomend goes I was looking at some threads earlier on bottomend rebuilds and some people had 300 hours on theirs and didnt. My opinion is if you changed the oil pretty regular and dont see alot of metal shavings in the oil or oilfilter then the bottomend should all right. As far as your question about the piston goes I would just stay with the oem because I dont think it would help that much as far as power goes or not enough to where you could really say" Holy ...."!

  • flintlock28

Posted April 05, 2007 - 05:15 PM

#3

The higher compression piston will give you more low-end and mid-range grunt. You'll also need to run higher octane fuel to prevent pre-ignition.....I think 100 is recommended for the 13.5:1. There's a guy on here somewhere (maybe Ga426 owner?) that really recommends going to the higher compression piston. I'm going to do the Piston/ rings after this season, and I'm leaning towards the 13.5:1.

  • grayracer513

Posted April 05, 2007 - 05:22 PM

#4

While you might think that 150-200 hours is a lot, my '03 450 has at least half again that many hours on it that I know of, and doesn't yet need to be rebuilt. It probably could benefit from it, though.

One nice thing about the 426 is that you can use the Yamaha stainless steel valves (the 2000 model came with them) to keep the cost of re-doing the head down.

I would consider replacing the crank. A complete crank will get you a new timing chain sprocket in the process; rebuilding won't. The risk, even when the rod clearance checks out OK, is the it is possible to have the needle cage fail, which IF it happens ( and it occasionally does ) the rod bearing will seize without warning.

The best source for your parts is TT OEM

Look the numbers up at the Yamaha site:
http://www.yamaha-mo...parts/home.aspx
and paste them in the search box, they'll come up.

If it doesn't work out for you, try crotchrocket,com

  • 642MX

Posted April 05, 2007 - 05:24 PM

#5

The higher compression piston will give you more low-end and mid-range grunt. You'll also need to run higher octane fuel to prevent pre-ignition.....I think 100 is recommended for the 13.5:1. There's a guy on here somewhere (maybe Ga426 owner?) that really recommends going to the higher compression piston. I'm going to do the Piston/ rings after this season, and I'm leaning towards the 13.5:1.


Some bikes need race fuel with 13.5:1 and some don't. For example, the KX250F comes from the factory with a 13.5:1 compression ratio and it only uses pump gas.

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  • 642MX

Posted April 05, 2007 - 05:29 PM

#6

Hey everyone, just wanted to say hello since this is my first post. I've been floating around for a while and reading this or that, so I figured I may as well join up.

Anyway I think I'm due for a rebuild on my '00 yz 426 since it probably has 150-200 hours on it. My question is how much am I probably going to have to throw in? I already plan on doing the valves, springs, piston & rings, but do I have to worry about the crank and rod as well (do these rods tend to stretch)? Also how are the Wiseco 13.5:1 pistons, are they worth it, or do they give much gains?

Any additional advice or recommendations would be appreciated as well

Thanks


I personally wouldn't replace the crank until it fails. The 13.5:1 pistons are the way to go. I noticed a lot more low end and mid-range snap. Be sure to do the 450 DCM while your in there.

I second http://www.crotchrocket.com, they have very good service and fair prices. :bonk:

  • Ebs

Posted April 05, 2007 - 06:59 PM

#7

I'm in the process of rebuilding my 426 as well. Should everything along with the cam timing chain be replaced...like the guides and tensioner?

  • SDBSKI

Posted April 05, 2007 - 07:40 PM

#8

Make sure you check the rod small end clearance and replace the rod if it's close to out of spec or gauled. Too much clearance will cause a rattle in the top end when the engine warms up even though the rod big end is fine. The 13:1 compression will also put more stress on the high time rod. I couldn't believe how cheap Yamaha parts are compared to Honda. I rebuilt a xr650L and it cost a fortune. The xr timing chain was three times the YZ.

  • BergArabia

Posted April 06, 2007 - 02:03 AM

#9

wow my 05 has about 100 hours on it and seems like a new bike to me.. I hadn't even thought of a rebuild coming up..

  • 642MX

Posted April 06, 2007 - 10:36 AM

#10

I'm in the process of rebuilding my 426 as well. Should everything along with the cam timing chain be replaced...like the guides and tensioner?


The 426 tensioner is really solid and so are the guides. I haven't replaced mine yet.

Now, the cam chain is the total opposite. They stretch easily and wear the crank gear if they aren't replaced regularly. I replace my cam chain once a year.





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