top end rebuild how often

6 replies to this topic
  • jasontms

Posted September 01, 2002 - 10:51 PM


How often should I rebuild the top end of my 00wr 400? It's got about 5000Km's on it now and have heard some scary stories about engine failures due to many Ks. Also is it realy as simple as they say to change the timming to yz spec?

  • Team_Oatmeal_Pie

Posted September 03, 2002 - 09:56 PM


I am wondering the same thing and was thinking a compression/leak down test could tell me if its needed. I am looking to find/purchase the kit to do it. Havent found one yet.

  • Dodger

Posted September 03, 2002 - 10:09 AM


Yo Jason,

Can't answer your first question, I'm hoping a top end will be years away for me.

BUT, to do YZ timing on these things is totally easy, check out Motoman393's site for very good instructions.

Dodger :) :D

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  • BrandonW

Posted September 03, 2002 - 10:33 AM


I recently tore my top end apart, trying to determine what may have caused my spark plug to ground out. (My engine suddenly shut down while doing 60 mph down the highway)

I pulled the spark plug, and the grounding rod was touching the electrode.

As it turns out, a portion of the slide plate from the carburator had broken off and was injested buy the engine.

My bike has a minimum of 8,000 miles on it, and the cylinder walls were perfect! The only marks on the walls were the swirl marks from a hone. No vertical scars what-so-ever.

I could not get my pressure gauge in the bike (did not have an adapter the circumfrence of the spark plug hole) but I don't think people really need to worry about top end rebuilds like you do with 2 strokes.

yeah, that is some great info for ya!



  • jasontms

Posted September 05, 2002 - 12:23 AM


Thank's for the reply guy's, sound's like I have no need to worry. I might give the YZ timing ago and see how it goes. :)

  • MN_Kevin

Posted September 05, 2002 - 01:38 AM


It cannot hurt to slap some rings on it. I know a street bike, 4 cylinder, will have ring wear at 10,000 miles (16093 klicks) and DOES benefit w/ a re-ring.

If you are going to do the YZ timing thing (or just inspecting your cylinder) and toying w/ new rings, it is easiest to do it at the same time.

As an FYI: If you have started your bike in water past the head vent (that runs down along your main frame's downtube) or started it in sand after biting it, you MAY just have SUCKED foreign material into your engine.

When starting your bike, the engine sucks on the tube. While running, the engine blows out this tube. I had 4 engine seizures AFTER starting my bike in 18" of water. I now have scoring in my cylinder and HAVE to repair it. I am opting for Eric Gorr, , to do his magic and install his 420 kit ~ $350.00.

If anyone wants to do the YZ timing thing, or pull the top end, there are a couple of VERY NICE things to know ahead of time, before it's too late. Feel free to ask!

  • xrracer36

Posted September 05, 2002 - 02:10 AM


i just put a top end in my 98. it was blowing smoke and i could easily push past tdc w/out lever. tore apart, and the piston was way outa spec, needed rings, and had some vertical scratches in cylinder (think i sucked something up thru the breather tube while starting in water or something along the way... ignorance sucks when you gotta pay for it down the road)
anyways, it wasn't cheap. had to have cylinder replated (millenium cylinders, very nice job, $165), new piston rings, wrist pin (usual top end stuff)(all oem yamaha), gaskets, spark plug. runs like new now. estimated damages... $400-$500 :)
and that's without a valve job, mine were still okay.
gained a lot of compression, runs better in general, don't smoke no more. :D
happy till the next expen$ive repair comes along. i'm guessing it will be the clutch. gonna wait till spring if i can.
racer 36 :D


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