WR400 Rebuild

Snap! I've just done exactly the same as you, bought a WR 400 cheap knowing that the engine was shot. Took the top off the engine the weekend and found the same as you, even down to the blued flywheels. Must get the cases apart next. As l only intend to use the bike for green lanes l will rebuild it back to the original spec. Good luck with the rebuild.

Hey guys, just a little update on the bike.

I pulled the gearbox down to have a look see and i found this little nasty:


Other than that ive been chasing all the parts for the bike. The last piece of the puzzle arived today. To start with we have a Vapor :excuseme: I bought it so i can measure the hours/kms the new motor does.


Second is a thumper talk decomp plug, im only showing this because the box it came in was quite funny :p


All the parts that arrived yesterday:


And my favorite.... HOT CAMS! I ended up going the hotcams route with a new 426 crankshaft, cylinder & piston :p:D If i had a good camera that takes macro shots id take a pic of the 426cm^2 cast into the cylinder heh


What she looks like right now, I've got a friend putting new seals in the forks & installing fork savers.


And here it is next to my mates brand new 2007 WR250. If my bike cant beat that when i finish ill be very :applause:


Another update, started putting the motor back together with the 426 bits :ride:

Brand New 426 Crankshaft


Ready to glue it together


Back together with everything turning freely, it actually took 3 attempts to get it right. The first two times I ****ed it up and the gearbox was bound up and wouldn't turn. I took the bottom end to a friend who just recently rebuilt his Wr400, when he put it together he just fluked it and it was fine. Turned out I had the shifter drum 180 degrees out, the reason is I was lining it up with the neutral switch, which I had installed upside down. Oh well, live and learn i guess, its all fine now and shifts perfectly.


Flywheel, counter balancer, stator etc all installed with a new side casing (old one had a huge puncture mark in it covered in araldite :S)


I busted a bolt when installing the shift segment so thats still on hold, I just got a phone call telling me its in stock now so ill go get the bolt this afternoon and finish the bottom end tonight :bonk: I'm still waiting on the head though :)

I'm just reading through your posts of your rebuild with great interest. I'm facing the same rebuild and have the exact same blue/heat marks on my 99 WR400 crank. I was thinking of doing the exact same thing as you did/doing. (i.e. WR426 crank assy, 426 cylinder and piston, Hot cams). I'm noticing the date of your posts. Have you been working this for a over a year?! Keep up the work, I'm going to refer to your postings during my rebuild, Thanks!

Looking good! :) BTW, my buddys 2000 YZ 426 had the same blue heat "markings", or whatever you want to call it. That cant be normal, could it?

Excellent thread. It should be a sticky for " complete engine rebuild"

just for the record, the blue markings are COMPLETELY normal. I bought a brand new 426 crankshaft and it had them as well. Its actually from when they heat it up to insert the crank pin (as i found out asking people who know more than me :) )

So after that i wasn't 100% sure the big end was actually gone, so i took the bottom end down to a motorbike workshop and showed him. The mechanic (head mechanic for craig dack racing in australia i believe) just ran some degreaser through the crankshaft and all of a sudden it was quite obvious. The oil takes up the clearance and makes it not seem as bad as it really is :S

As for an update i busted the clutch basket 2 days ago installing it, so i ordered a new one and took the bottom end down to get them to install it for me :ride: Tonight ill be finishing the bottom end, the only other thing I'm waiting on is the head.

It hasn't taken me a year for the rebuild, i got a problem with starting things and never finishing them. The dates in the thread are correct but i only do little bits at a time, like when i pulled the motor out it sat for a few months, then i got the head off and it sat for over a year, then i got back into it :bonk: (a year ago i didn't have anyone to ride with but now all my mates are buying bikes and my cousins all have new bikes :S )

If the heads done today (ill be ringing my head guy soon) i should have it running sunday, otherwise ill finish the bottom end and install it into the frame so the only thing i gotta do is install the head. I cant wait for this :D:D

As for sticky? I don't think my thread is worth that, theres on in the YZ250f section that is much more detailed, ive even been using pics from it for reference :busted:

Man your gonna love that. I did the 444 on my WR400 and its right behind my buddies 05 KTM 525. A few more tweaks and Im right there!

Good luck

nice :)

I'm hoping to get up with the 06/07 WR450s that my dad/uncle ride, not sure if this will do that but it cant be far off :ride:

All I've got to do now is put coolant and oil in it and start the bastard :bonk: ill post updated pictures later :D:D:D

Here comes the best update of all :ride:

Motor fully assembled


Installed in the bike




This is the coolest thing ive seen, i went to buy a plastic funnel and i found it. Fits right into the oil hole snug and u just bend it up how u want, works a treat :bonk:


The finished bike!


So how does it go? AWESOME! I haven't had time to give it a good ride as a rather large oil leak surfaced. The oil pipe that connects the head to the cases is leaking, so ill ill go get new brass washers tomorrow (typical! the only part I don't replace leaks as usual :) )

Ive only ridden it in the dark with no headlight so ill give it a good run tomorrow.

Ill try and get some video of it up for yas :D

congrats on a successful rebuild! Glad you got around to taking all the pictures I forgot to...brings back lots of memories

nice, get that leak fixed and go toe to toe with a 450 asap... i swear mine would take a stock 450 all day long!

Have fun.


All the pics are located here, just over 100 of them.


Yes ill definatly trying to drag some 450's, my old man has an 07 wr450 and my uncle has an 06 wr450 so i shouldn't have trouble finding someone to drag

I know one thing, I'm going to have to learn to ride again! I was just getting good on my old slug DR350, i could even keep up with my cousin on his wr250 in the right circumstances. Now its a whole new ball game :) aside from ~30 mins of riding when i got the wr400, i haven't really ridden it.

Bikes got 200k's on her now, just preparing for a desert ride this weekend (~800k's) cant wait.

Bikes 98% finished now, last Thursday it started dumping coolant out of the water pump weep hole so just waiting on a new shaft so i can put it back together for this weekend.

Ended up replacing the handlebars with Tag T2's, and barkbusters. Mounted the trailtech on the stock speedo mount, working great so far, just on a ride in the wet the speedo stoped working, started working again the next day though so i presume it was water. So i elec taped up the wiring as much as possible to try stop that. Installed my bumtank (4 ltr auxiliary tank that sits on the back of the bike, don't even notice its there!).

Here be some pictures



Unfortunately it looks like this right now :thumbsup:


Next mod after the desert ride i think ill replace the rear brake master cyl/slave cyl with bits from a later model, my reservoir is starting to melt and its the gheyest idea ever, newer model ones are much better.

Great thread! I'm almost doing the same thing! I'm just about ready to split the case and see what's going on in the gearbox. The pictures have been great and give me a good reference as I'm pulling everything apart!

Nice work! Can't wait till mines back together and running!

Just a little update, the bikes been trouble free for 1000k's so far, im very happy with how it goes.

I lined it up with a 06 wr450 on a desert road with a much lighter rider than me, the only mods on it was a staintune exhaust (same as mine) with jetting to suit. I left it for dead up to ~100-105kmh where the top end of the 450 took over, im very happy with how the bike is performing. Its got plenty of spastic power when you want it but its easy to ride :D

aside from playing on the farm I've done 2 rides so far, a 600k one in the desert and 200k's in rocky bush. Got some pics & video if anyones interested:

Desert ride:


Video of desert ride, I'm the guy that stuffs up the hill climb :D

Rocky bush ride, was just an easy one as my mates are new to bikes and are still learning how to ride.




Hi can anyone help me ? I have herd 0f the grey wire mod on WR400s but i not sure what to do. Im told it gives you more power ! That sounds too good to be true so any news will be good news. Thanks !

So how much did you end up spending?

I'm scared to work it out :D considering i got the bike for free though it wasn't that bad.

I worked it out that a dodge rebuild without replacing the crank would be around ~900$. The rebuild woulda cost ~1300$ in parts with a whole new crankshaft. Then theres what i did, which included new cylinder, 426 crankshaft/drive gear & cams. So somewhere b/w 2-3k$, i replaced alot of shit though. Overall I'm very happy with the bike :D I just got back from a few laps at the local MX track and im buggered. Had a hard time holding on :D


so one ride after i finally solved the throttle slide problems my bike was stolen last night.

If anyone in Melbourne, Australia (stolen from south east side near moorabin airport) sees anything please give me a bell, the rego is YT385

So some stinken ass theif is now running around on a super reliable super fast & easy to start wr426 :thumbsup:


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