Wr 426 2002 Build Thread (starts from box) Bringing Back The Thump

3 replies to this topic
  • zwebx

Posted July 04, 2014 - 02:36 AM


Okay bought this wr off ebay For $650 This is my post from miniriders, thought it would be cool to share it here too.. Warning picture heavy..

Edited by zwebx, July 04, 2014 - 02:45 AM.

  • zwebx

Posted July 04, 2014 - 02:38 AM


will be a good project, what does it need?

So far, head (maybe can repair this one but dont want to depends on $$)
Will buy new camchain, valves for replacement head.. maybe re-coat the bore(s) one for a spare.. Needs fork seals Maybe some missalanious parts for the engine but nothing major.. Going to buy all new bearings seals etc and rod kit.

The one crank thats mangled (assume piston skirt gave way) has a good cam gear sprocket 

The spare one thats not mangled has a slightly warn rod (wont use it but could) but the cam gear is quite shagged.. 

Also need a new tank, have been looking at Yamaha WR250 & WR450 26 litres | 7-Yamaha | Safari Tanks - Safari Tanks

Dont mind waiting a few pay checks and will be living off rations to make it all work :p

Needs a seat, front tyre and some tlc all round would like to get the frame powdercoated (not sure what colour) but will see... 

Dont mind tipping money into this bike as i see no better one in the world :p (okay maybe the 2012 model would be nice with efi and alloy frame and better front end grip etc.. For now id prefer to live out of debt as much as possible... smile.png stress is not my thing and if i cant get work for a week, **** it i will go out and ride biggrin.png

ouch..... did it drop a valve?

but thats not a bad score!
whats your plans for the head and the crank....?? ie; how ya gunna fix it?
Head im not sure yet, could replace the valve seat and re-use it after smoothing out the dent as because its not on the gasket surface..

Crank i think i will go a new one.. if i can afford it or just use the better (not munted one) for a while till i have the funds up because the cam chain sprocket is on its way out *Just usable*

More pics to come fellas


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  • zwebx

Posted July 04, 2014 - 02:40 AM


attachment.php?attachmentid=10254&stc=1 Aha a problem, Someone must of hated life at one stage lol.. No problem for me, heres a picture of the solution

attachment.php?attachmentid=10255&stc=1 A six point socket, tapped on with a hammer and i was bound to get it off

attachment.php?attachmentid=10256&stc=1 Much to my relief, the threads are okay... Time to add a magnetic drain bolt to my list
Assembled the kicker, and shifter assembly today (just a little mock up) Heres a pic of the crank im going to use and that i believe was with the bike originally.
New rod and she will be fine smile.png im a little worried about the cam sprocket wear:
attachment.php?attachmentid=10258&stc=1 Buut looks like i will keep an eye out on it and watch ebay for a good one
Sussed out all the gears i need, waiting on payday now.. smile.png

  • zwebx

Posted July 04, 2014 - 02:43 AM


How the motor is sitting at the moment (test jigging it all up)

Parts finally arrived in the mail (well the most $$ heavy one)

New head (used of course) But great condition for its age

Okay, looks good from the outside.. 
How do i know its sound mechanically..

Step One: Remove cam caps (remember cross pattern) 
And inspect the rear cam bearing for wear, scores etc


Step two: Remove cams and inspect the cam lobes for damage..
Now remove the shim buckets and including shims (also inspect for side to side play)
You can see, i just used magnets.. dont want to scratch up the sides.. also inspect the sides for damage/wear mainly just scratches etc.. gives you a good idea how many hrs your head has run

Step Three: Remove the valve springs +collets.. I found the easiest way to do this is to use a long socket that sits on the edge of the spring retainer 
eg.in this case my spark plug socket was a perfect fit
And then pull the valve down approx to where the cam would lift it too And then wriggle it from side to side all ways.. there should be little play this is also a good indicator of the condition of your valve guides/valve stems.
I should be using a dial gauge and a magnetic base, but these are fine and i believe are in spec. (also dont have one frown.png ) Pretty much if either of these are too warn then replace them. You dont want to cause wear of the valve head from having it been forced into place each rotation. then eventually failing.

Step Four:
Inspect the valve seats
You can see.. Mine have a little carbon built up on them (causes sealing problems) So i will clean them thoroughly. 
Focus on the 45deg angle that is the only one that seals 
also clean up the rest of your head if you feel up to it... may end up polishing mine to get rid of the buildup.

You can see my valve seats look like they will have no issue sealing (as checked so far)

Next up (in progress) How to check the life left in your valves and guides (black marker trick)

Here is a picture of one intake valve... You can see the shiny part of it is the 45 degrees, or the sealing surface. This is the area i will be focusing on this post.. This will be quite a easy thing to do while you "bang in a new top end" youd be suprised how many people (not mechaincs) do not bother to do this.. i have even heard stories of never checking valves for years...

Anyway, now the valves are removed from the head all in order (i like to put the head upside down on the table with the cam chain side toward me then lay them down in order infront of the head)
grab a sharpie (or blueing if you have any) this is the "no tools method" that i will use...
Coat the entire valve, or valve seat your choice in my case i coated the valve.. now while its wet push the valve into the correct position on the head and push it down and spin it a couple of times.. 
Here is the coating left on the valve seat, note not a good example the sharpie dried a little before i did it i did this again afterwards but forgot to take a photo of it..
This gives you a good idea of where the valve is coming in contact with the head.
There are specifications in the manual of how much surface area there is meant to be, or the whole 45deg angle to be safe..
Also look at the valve and there should be a clear surface where the sharpie rubbed off.. this is the contact area that the valve uses for sealing and also cooling. If this area is compromised in any way eg.. carbon dirt etc this can cause the valve to over heat and damage the seal etc then cause more damage to the motor.
I always check this area of the valve before i re-use it.. thankfully mine are looking good (at 130 a valve there not cheap to replace) My seats could be better but a may lap the valves in to correct them (They are ti valves with no coating) not sure if im meant to or not? but there leaking a bit so i want too.

Time to clean as im waiting for the $$ to buy some parts 

Some elbow grease later:.........|


Some good stuff right here


Okay a recent development.. After test jigging up pretty much the whole motor i have come to find the nice shineyish crank to be from another bike.. the dented and nasty one Is the only one that would have come with the bike.. 
What makes me say that?
The right hand side where the drive gears fit on have a different spline assembly, the nicer one coming from a wr 400 (with a 426 rod) that could be usable but the different drive assembly means i would have to buy almost the same value as the new crank in gears and other fittings..

The current rod on this crank seems usable but the death of this motor was a piston breakage the rod is straight but does have one minor mark on it But for the extra $150 id prefer to wait and put that into it before i put the cases back together..


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